



SDCC Compiler User Guide

SDCC 2.8.0
$Date:: 2008-03-14#$ 
$Revision: 5096 $



Table of Contents

    Chapter 1 Introduction
        1.1 About SDCC
        1.2 Open Source
        1.3 Typographic conventions
        1.4 Compatibility with previous versions
        1.5 System Requirements
        1.6 Other Resources
        1.7 Wishes for the future
    Chapter 2 Installing SDCC
        2.1 Configure Options
        2.2 Install paths
        2.3 Search Paths
        2.4 Building SDCC
            2.4.1 Building SDCC on Linux
            2.4.2 Building SDCC on Mac OS X
            2.4.3 Cross compiling SDCC on Linux for Windows
            2.4.4 Building SDCC using Cygwin and Mingw32
            2.4.5 Building SDCC Using Microsoft Visual C++ 6.0/NET (MSVC)
            2.4.6 Building SDCC Using Borland
            2.4.7 Windows Install Using a ZIP Package
            2.4.8 Windows Install Using the Setup Program
            2.4.9 VPATH feature
        2.5 Building the Documentation
        2.6 Reading the Documentation
        2.7 Testing the SDCC Compiler
        2.8 Install Trouble-shooting
            2.8.1 If SDCC does not build correctly
            2.8.2 What the "./configure" does
            2.8.3 What the "make" does
            2.8.4 What the "make install" command does.
        2.9 Components of SDCC
            2.9.1 sdcc - The Compiler
            2.9.2 sdcpp - The C-Preprocessor
            2.9.3 asxxxx, aslink, link-xxx - The Assemblers and Linkage Editors
            2.9.4 s51 - The Simulator
            2.9.5 sdcdb - Source Level Debugger
    Chapter 3 Using SDCC
        3.1 Compiling
            3.1.1 Single Source File Projects
            3.1.2 Postprocessing the Intel Hex file
            3.1.3 Projects with Multiple Source Files
            3.1.4 Projects with Additional Libraries
            3.1.5 Using sdcclib to Create and Manage Libraries
        3.2 Command Line Options
            3.2.1 Processor Selection Options
            3.2.2 Preprocessor Options
            3.2.3 Linker Options
            3.2.4 MCS51 Options
            3.2.5 DS390 / DS400 Options
            3.2.6 Z80 Options
            3.2.7 GBZ80 Options
            3.2.8 Optimization Options
            3.2.9 Other Options
            3.2.10 Intermediate Dump Options
            3.2.11 Redirecting output on Windows Shells
        3.3 Environment variables
        3.4 Storage Class Language Extensions
            3.4.1 MCS51/DS390 Storage Class Language Extensions
                3.4.1.1 data / near
                3.4.1.2 xdata / far
                3.4.1.3 idata
                3.4.1.4 pdata
                3.4.1.5 code
                3.4.1.6 bit
                3.4.1.7 sfr / sfr16 / sfr32 / sbit
                3.4.1.8 Pointers to MCS51/DS390 specific memory spaces
                3.4.1.9 Notes on MCS51 memory layout
            3.4.2 Z80/Z180 Storage Class Language Extensions
                3.4.2.1 sfr (in/out to 8-bit addresses)
                3.4.2.2 banked sfr (in/out to 16-bit addresses)
                3.4.2.3 sfr (in0/out0 to 8 bit addresses on Z180/HD64180)
            3.4.3 HC08 Storage Class Language Extensions
                3.4.3.1 data 
                3.4.3.2 xdata 
        3.5 Absolute Addressing
        3.6 Parameters & Local Variables
        3.7 Overlaying
        3.8 Interrupt Service Routines
            3.8.1 General Information
                3.8.1.1 Common interrupt pitfall: variable not declared volatile
                3.8.1.2 Common interrupt pitfall: non-atomic access
                3.8.1.3 Common interrupt pitfall: stack overflow
                3.8.1.4 Common interrupt pitfall: use of non-reentrant functions
            3.8.2 MCS51/DS390 Interrupt Service Routines
            3.8.3 HC08 Interrupt Service Routines
            3.8.4 Z80 Interrupt Service Routines
        3.9 Enabling and Disabling Interrupts
            3.9.1 Critical Functions and Critical Statements
            3.9.2 Enabling and Disabling Interrupts directly
            3.9.3 Semaphore locking (mcs51/ds390)
        3.10 Functions using private register banks (mcs51/ds390)
        3.11 Startup Code
            3.11.1 MCS51/DS390 Startup Code
            3.11.2 HC08 Startup Code
            3.11.3 Z80 Startup Code
        3.12 Inline Assembler Code
            3.12.1 A Step by Step Introduction
            3.12.2 Naked Functions
            3.12.3 Use of Labels within Inline Assembler
        3.13 Interfacing with Assembler Code
            3.13.1 Global Registers used for Parameter Passing
            3.13.2 Registers usage
            3.13.3 Assembler Routine (non-reentrant)
            3.13.4 Assembler Routine (reentrant)
        3.14 int (16 bit) and long (32 bit) Support
        3.15 Floating Point Support
        3.16 Library Routines
            3.16.1 Compiler support routines (_gptrget, _mulint etc.)
            3.16.2 Stdclib functions (puts, printf, strcat etc.)
                3.16.2.1 <stdio.h>
                3.16.2.2 <malloc.h>
            3.16.3 Math functions (sinf, powf, sqrtf etc.)
                3.16.3.1 <math.h>
            3.16.4 Other libraries
        3.17 Memory Models
            3.17.1 MCS51 Memory Models
                3.17.1.1 Small, Medium and Large
                3.17.1.2 External Stack
            3.17.2 DS390 Memory Model
        3.18 Pragmas
        3.19 Defines Created by the Compiler
    Chapter 4 Notes on supported Processors
        4.1 MCS51 variants
            4.1.1 pdata access by SFR 
            4.1.2 Other Features available by SFR
            4.1.3 Bankswitching
                4.1.3.1 Hardware
                4.1.3.2 Software
        4.2 DS400 port
        4.3 The Z80 and gbz80 port
        4.4 The HC08 port
        4.5 The PIC14 port
            4.5.1 PIC Code Pages and Memory Banks
            4.5.2 Adding New Devices to the Port 
            4.5.3 Interrupt Code
            4.5.4 Linking and Assembling
            4.5.5 Command-Line Options
            4.5.6 Environment Variables
            4.5.7 The Library
                4.5.7.1 error: missing definition for symbol ``__gptrget1''
                4.5.7.2 Processor mismatch in file ``XXX''.
            4.5.8 Known Bugs
                4.5.8.1 Function arguments
                4.5.8.2 Regression tests fail
        4.6 The PIC16 port
            4.6.1 Global Options
            4.6.2 Port Specific Options
                4.6.2.1 Code Generation Options
                4.6.2.2 Optimization Options
                4.6.2.3 Assembling Options
                4.6.2.4 Linking Options
                4.6.2.5 Debugging Options
            4.6.3 Enviroment Variables
            4.6.4 Preprocessor Macros
            4.6.5 Directories
            4.6.6 Pragmas
            4.6.7 Header Files
            4.6.8 Libraries
                Building the libraries
            4.6.9 Adding New Devices to the Port
            4.6.10 Memory Models
            4.6.11 Stack
            4.6.12 Functions
            4.6.13 Function return values
            4.6.14 Interrupts
            4.6.15 Generic Pointers
            4.6.16 PIC16 C Libraries
                4.6.16.1 Standard I/O Streams
                4.6.16.2 Printing functions
                4.6.16.3 Signals
            4.6.17 PIC16 Port -- Tips
                4.6.17.1 Stack size
            4.6.18 Known Bugs
    Chapter 5 Debugging
        5.1 Debugging with SDCDB 
            5.1.1 Compiling for Debugging
            5.1.2 How the Debugger Works
            5.1.3 Starting the Debugger SDCDB
            5.1.4 SDCDB Command Line Options
            5.1.5 SDCDB Debugger Commands
                break [line | file:line | function | file:function]
                clear [line | file:line | function | file:function ]
                continue
                finish
                delete [n]
                info [break | stack | frame | registers ]
                step
                next
                run
                ptype variable 
                print variable
                file filename
                frame
                set srcmode
                ! simulator command
                quit
            5.1.6 Interfacing SDCDB with DDD
            5.1.7 Interfacing SDCDB with XEmacs
    Chapter 6 TIPS
        6.1 Porting code from or to other compilers
        6.2 Tools included in the distribution
        6.3 Documentation included in the distribution
        6.4 Related open source tools
        6.5 Related documentation / recommended reading
        6.6 Application notes specifically for SDCC
        6.7 Some Questions
    Chapter 7 Support
        7.1 Reporting Bugs
        7.2 Requesting Features
        7.3 Submitting patches
        7.4 Getting Help
        7.5 ChangeLog
        7.6 Subversion Source Code Repository
        7.7 Release policy
        7.8 Examples
        7.9 Quality control
        7.10 Use of SDCC in Education
    Chapter 8 SDCC Technical Data
        8.1 Optimizations
            8.1.1 Sub-expression Elimination
            8.1.2 Dead-Code Elimination
            8.1.3 Copy-Propagation
            8.1.4 Loop Optimizations
            8.1.5 Loop Reversing
            8.1.6 Algebraic Simplifications
            8.1.7 'switch' Statements
            8.1.8 Bit-shifting Operations.
            8.1.9 Bit-rotation
            8.1.10 Nibble and Byte Swapping
            8.1.11 Highest Order Bit / Any Order Bit
            8.1.12 Higher Order Byte / Higher Order Word
            8.1.13 Peephole Optimizer
        8.2 ANSI-Compliance
        8.3 Cyclomatic Complexity
        8.4 Retargetting for other Processors
    Chapter 9 Compiler internals
        9.1 The anatomy of the compiler
        9.2 A few words about basic block successors, predecessors and dominators
    Chapter 10 Acknowledgments
        Alphabetical index



Introduction

1.1 About SDCC

SDCC (Small Device C Compiler) is free open source, 
retargettable, optimizing ANSI-C compiler by Sandeep 
Dutta designed for 8 bit Microprocessors. The current 
version targets Intel MCS51 based Microprocessors 
(8031, 8032, 8051, 8052, etc.), Dallas DS80C390 
variants, Freescale (formerly Motorola) HC08 and Zilog 
Z80 based MCUs. It can be retargeted for other 
microprocessors, support for Microchip PIC, Atmel AVR 
is under development. The entire source code for the 
compiler is distributed under GPL. SDCC uses ASXXXX & ASLINK
, an open source retargetable assembler & linker. SDCC 
has extensive language extensions suitable for 
utilizing various microcontrollers and underlying 
hardware effectively. 

In addition to the MCU specific 
optimizations SDCC also does a host of standard 
optimizations like:

* global sub expression elimination, 

* loop optimizations (loop invariant, strength 
  reduction of induction variables and loop reversing), 

* constant folding & propagation, 

* copy propagation, 

* dead code elimination 

* jump tables for switch statements.

For the back-end SDCC uses a global register allocation 
scheme which should be well suited for other 8 bit 
MCUs. 

The peep hole optimizer uses a rule based 
substitution mechanism which is MCU independent. 


Supported data-types are:

+------------+-----------------------+-------------+-----------------------------------+------------------------------------+
|  

type    |       

width         | 

default   |          

signed range           | 

unsigned range                   |
+------------+-----------------------+-------------+-----------------------------------+------------------------------------+
+------------+-----------------------+-------------+-----------------------------------+------------------------------------+
|  

bool    |       

1 bit         | 

unsigned  |               

-                 | 

0, 1                             |
+------------+-----------------------+-------------+-----------------------------------+------------------------------------+
|  

char    |   

8 bits, 1 byte    |  

signed   |           

-128, +127            | 

0, +255                          |
+------------+-----------------------+-------------+-----------------------------------+------------------------------------+
|  

short   |  

16 bits, 2 bytes   |  

signed   |        

-32.768, +32.767         | 

0, +65.535                       |
+------------+-----------------------+-------------+-----------------------------------+------------------------------------+
|   

int    |  

16 bits, 2 bytes   |  

signed   |        

-32.768, +32.767         | 

0, +65.535                       |
+------------+-----------------------+-------------+-----------------------------------+------------------------------------+
|  

long    |  

32 bits, 4 bytes   |  

signed   | 

-2.147.483.648, +2.147.483.647  | 

0, +4.294.967.295                |
+------------+-----------------------+-------------+-----------------------------------+------------------------------------+
+------------+-----------------------+-------------+-----------------------------------+------------------------------------+
|  

float   |  

4 bytes IEEE 754   |  

signed   |                

                 | 

1.175494351E-38, 3.402823466E+38 |
+------------+-----------------------+-------------+-----------------------------------+------------------------------------+
+------------+-----------------------+-------------+-----------------------------------+------------------------------------+
| 

pointer  | 

1, 2, 3 or 4 bytes  | 

generic   |                

                 | 

                                 |
+------------+-----------------------+-------------+-----------------------------------+------------------------------------+


The compiler also allows inline assembler code to be 
embedded anywhere in a function. In addition, routines 
developed in assembly can also be called.

SDCC also 
provides an option (--cyclomatic) to report the 
relative complexity of a function. These functions can 
then be further optimized, or hand coded in assembly if 
needed. 

SDCC also comes with a companion source level 
debugger SDCDB. The debugger currently uses ucSim, a 
free open source simulator for 8051 and other micro-controllers.


The latest SDCC version can be downloaded from [http://sdcc.sourceforge.net/snap.php]. Please 
note: the compiler will probably always be some steps 
ahead of this documentation

Obviously this has pros and cons
.

1.2 Open Source

All packages used in this compiler system are open 
source and freeware; source code for all the 
sub-packages (pre-processor, assemblers, linkers etc.) 
is distributed with the package. This documentation is 
maintained using a free open source word processor (LyX).

This program is free software; you can redistribute it 
and/or modify it under the terms of the GNU General 
Public License as published by the Free Software 
Foundation; either version 2, or (at your option) any 
later version. This program is distributed in the hope 
that it will be useful, but WITHOUT ANY WARRANTY; 
without even the implied warranty of MERCHANTABILITY or 
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General 
Public License for more details. You should have 
received a copy of the GNU General Public License along 
with this program; if not, write to the Free Software 
Foundation, 59 Temple Place - Suite 330, Boston, MA 
02111-1307, USA. In other words, you are welcome to 
use, share and improve this program. You are forbidden 
to forbid anyone else to use, share and improve what 
you give them. Help stamp out software-hoarding! 

1.3 Typographic conventions

Throughout this manual, we will use the following 
convention. Commands you have to type in are printed in 
"sans serif". Code samples are printed in typewriter 
font. Interesting items and new terms are printed in italic.

1.4 Compatibility<sec:Compatibility-with-previous> with previous versions

Newer versions have usually numerous bug fixes compared 
with the previous version. But we also sometimes 
introduce some incompatibilities with older versions. 
Not just for the fun of it, but to make the compiler 
more stable, efficient and ANSI compliant (see section [sub:ANSI-Compliance] 
for ANSI-Compliance). 


* short is now equivalent to int (16 bits), it used to 
  be equivalent to char (8 bits) which is not ANSI 
  compliant. To maintain compatibility, old programs 
  may be compiled using the --short-is-8bits 
  commandline option (see [lyx:--short-is-8bits]).

* the default directory for gcc-builds where include, 
  library and documentation files are stored is now in 
  /usr/local/share.

* char type parameters to vararg functions are casted 
  to int unless explicitly casted and --std-c89 and --std-c99
   command line option are not defined 

 !
  , e.g.: 
  char a=3;
  printf ("%d %c\n", a, (char)a);
 will 
  push a as an int and as a char resp if --std-c89 and --std-c99
   command line options are not defined,
 will push a as 
  two ints if --std-c89 or --std-c99 command line 
  option is defined.

* option --regextend has been removed.

* option --noregparms has been removed.

* option --stack-after-data has been removed.

* bit and sbit types now consistently behave like the 
  C99 _Bool type with respect to type conversion. The 
  most common incompatibility resulting from this 
  change is related to bit toggling idioms, e.g.:
  bit b;
  
  b = ~b; /* equivalent to b=1 instead of toggling b */

 !
  
  b = !b; /* toggles b */
In previous versions, both 
  forms would have toggled the bit.

<pending: more incompatibilities?>

1.5 System Requirements

What do you need before you start installation of SDCC? 
A computer, and a desire to compute. The preferred 
method of installation is to compile SDCC from source 
using GNU gcc and make. For Windows some pre-compiled 
binary distributions are available for your 
convenience. You should have some experience with 
command line tools and compiler use.

1.6 Other Resources

The SDCC home page at [http://sdcc.sourceforge.net/] is a great place to find 
distribution sets. You can also find links to the user 
mailing lists that offer help or discuss SDCC with 
other SDCC users. Web links to other SDCC related sites 
can also be found here. This document can be found in 
the DOC directory of the source package as a text or 
HTML file. A pdf version of this document is available 
at [http://sdcc.sourceforge.net/doc/sdccman.pdf]. Some of the other tools (simulator and assembler) 
included with SDCC contain their own documentation and 
can be found in the source distribution. If you want 
the latest unreleased software, the complete source 
package is available directly from Subversion on 
https://sdcc.svn.sourceforge.net/svnroot/sdcc/trunk/sdcc.

1.7 Wishes for the future

There are (and always will be) some things that could 
be done. Here are some I can think of:


char KernelFunction3(char p) at 0x340;


better code banking support for mcs51

If you can think 
of some more, please see the section [sub:Requesting-Features] about filing 
feature requests.


Installing SDCC

For most users it is sufficient to skip to either 
section [sub:Building-SDCC-on-Linux] (Unix) or section [sub:Windows-Install] (Windows). More detailed 
instructions follow below.

2.1 Configure Options

The install paths, search paths and other options are 
defined when running 'configure'. The defaults can be 
overridden by:

--prefix see table below

--exec_prefix see table below

--bindir see table below

--datadir see table below

--datarootdir see table below


  docdir environment variable, see table below

  include_dir_suffix environment variable, see table below

  lib_dir_suffix environment variable, see table below

  sdccconf_h_dir_separator environment variable, either / 
or \\ makes sense here. This character will only be 
used in sdccconf.h; don't forget it's a C-header, 
therefore a double-backslash is needed there.


--disable-mcs51-port Excludes the Intel mcs51 port

--disable-gbz80-port Excludes the Gameboy gbz80 port

--disable-z80-port Excludes the z80 port

--disable-avr-port Excludes the AVR port

--disable-ds390-port Excludes the DS390 port

--disable-hc08-port Excludes the HC08 port

--disable-pic-port Excludes the PIC14 port

--disable-pic16-port Excludes the PIC16 port

--disable-xa51-port Excludes the XA51 port

--disable-ucsim Disables configuring and building of ucsim

--disable-device-lib Disables automatically building 
device libraries

--disable-packihx Disables building packihx


--enable-doc Build pdf, html and txt files from the lyx sources

--enable-libgc Use the Bohem memory allocator. Lower 
runtime footprint.

Furthermore the environment variables CC, CFLAGS, ... 
the tools and their arguments can be influenced. Please 
see `configure --help' and the man/info pages of 
`configure' for details.

The names of the standard 
libraries STD_LIB, STD_INT_LIB, STD_LONG_LIB, 
STD_FP_LIB, STD_DS390_LIB, STD_XA51_LIB and the 
environment variables SDCC_DIR_NAME, SDCC_INCLUDE_NAME, 
SDCC_LIB_NAME are defined by `configure' too. At the 
moment it's not possible to change the default settings 
(it was simply never required).

These configure options 
are compiled into the binaries, and can only be changed 
by rerunning 'configure' and recompiling SDCC. The 
configure options are written in italics to distinguish 
them from run time environment variables (see section 
search paths).

The settings for "Win32 builds" are used by 
the SDCC team to build the official Win32 binaries. The 
SDCC team uses Mingw32 to build the official Windows 
binaries, because it's

1. open source, 

2. a gcc compiler and last but not least

3. the binaries can be built by cross compiling on SDCC 
  Distributed Compile Farm.

See the examples, how to pass the Win32 settings to 
'configure'. The other Win32 builds using Borland, VC 
or whatever don't use 'configure', but a header file 
sdcc_vc_in.h is the same as sdccconf.h built by 
'configure' for Win32.

These defaults are:


+-----------------------+--------------------------+--------------------+
| 

Variable            | 

default                | 

Win32 builds     |
+-----------------------+--------------------------+--------------------+
+-----------------------+--------------------------+--------------------+
| 

PREFIX              | 

/usr/local             | 

\sdcc            |
+-----------------------+--------------------------+--------------------+
| 

EXEC_PREFIX         | 

$PREFIX                | 

$PREFIX          |
+-----------------------+--------------------------+--------------------+
| 

BINDIR              | 

$EXEC_PREFIX/bin       | 

$EXEC_PREFIX\bin |
+-----------------------+--------------------------+--------------------+
| 

DATADIR             | 

$DATAROOTDIR           | 

$DATAROOTDIR     |
+-----------------------+--------------------------+--------------------+
| 

DATAROOTDIR         | 

$PREFIX/share          | 

$PREFIX          |
+-----------------------+--------------------------+--------------------+
| 

DOCDIR              | 

$DATAROOTDIR/sdcc/doc  | 

$DATAROOTDIR\doc |
+-----------------------+--------------------------+--------------------+
| 

INCLUDE_DIR_SUFFIX  | 

sdcc/include           | 

include          |
+-----------------------+--------------------------+--------------------+
| 

LIB_DIR_SUFFIX      | 

sdcc/lib               | 

lib              |
+-----------------------+--------------------------+--------------------+



'configure' also computes relative paths. This is 
needed for full relocatability of a binary package and 
to complete search paths (see section search paths below):

 

+------------------------+---------------+----------------+
| 

Variable (computed)  | 

default     | 

Win32 builds |
+------------------------+---------------+----------------+
+------------------------+---------------+----------------+
| 

BIN2DATA_DIR         | 

../share    | 

..           |
+------------------------+---------------+----------------+
| 

PREFIX2BIN_DIR       | 

bin         | 

bin          |
+------------------------+---------------+----------------+
| 

PREFIX2DATA_DIR      | 

share/sdcc  | 

             |
+------------------------+---------------+----------------+



Examples:

./configure
./configure --prefix="/usr/bin" --datarootdir="/usr/share"

./configure --disable-avr-port --disable-xa51-port

To cross compile on linux for Mingw32 (see also 
'sdcc/support/scripts/sdcc_mingw32'):

./configure \
CC="i586-mingw32msvc-gcc" CXX="i586-mingw32msvc-g++"
 \ 
RANLIB="i586-mingw32msvc-ranlib" \
STRIP="i586-mingw32msvc-strip"
 \
--prefix="/sdcc" \
--datarootdir="/sdcc" \
docdir="\${datarootdir}/doc"
 \
include_dir_suffix="include" \
lib_dir_suffix="lib" \

sdccconf_h_dir_separator="\\\\" \
--disable-device-lib\
-
-host=i586-mingw32msvc\
--build=unknown-unknown-linux-gnu

To "cross"compile on Cygwin for Mingw32 (see also 
sdcc/support/scripts/sdcc_cygwin_mingw32):

./configure -C \
--prefix="/sdcc" \
--datarootdir="/sdcc" \
docdir="
\${datarootdir}/doc" \ 
include_dir_suffix="include" \
lib_dir_suffix="
lib" \
sdccconf_h_dir_separator="\\\\" \
CC="gcc -mno-cygwin" \
CXX="
g++ -mno-cygwin" 

'configure' is quite slow on Cygwin (at least on 
windows before Win2000/XP). The option '--C' turns on 
caching, which gives a little bit extra speed. However 
if options are changed, it can be necessary to delete 
the config.cache file.

2.2 Install paths<sub:Install-paths>





+-------------------+----------------------------------+----------------------------------+-----------------+
| 

Description     | 

Path                           | 

Default                        | 

Win32 builds  |
+-------------------+----------------------------------+----------------------------------+-----------------+
+-------------------+----------------------------------+----------------------------------+-----------------+
| 

Binary files*   | 

$EXEC_PREFIX                   | 

/usr/local/bin                 | 

\sdcc\bin     |
+-------------------+----------------------------------+----------------------------------+-----------------+
| 

Include files   | 

$DATADIR/ $INCLUDE_DIR_SUFFIX  | 

/usr/local/share/sdcc/include  | 

\sdcc\include |
+-------------------+----------------------------------+----------------------------------+-----------------+
| 

Library file**  | 

$DATADIR/$LIB_DIR_SUFFIX       | 

/usr/local/share/sdcc/lib      | 

\sdcc\lib     |
+-------------------+----------------------------------+----------------------------------+-----------------+
| 

Documentation   | 

$DOCDIR                        | 

/usr/local/share/sdcc/doc      | 

\sdcc\doc     |
+-------------------+----------------------------------+----------------------------------+-----------------+


*compiler, preprocessor, assembler, and linker
**the 
model is auto-appended by the compiler, e.g. small, 
large, z80, ds390 etc

The install paths can still be changed during `make 
install' with e.g.:

make install prefix=$(HOME)/local/sdcc

Of course this doesn't change the search paths compiled 
into the binaries.

Moreover the install path can be 
changed by defining DESTDIR:

make install DESTDIR=$(HOME)/sdcc.rpm/

Please note that DESTDIR must have a trailing slash!

2.3 Search Paths<sub:Search-Paths>

Some search paths or parts of them are determined by 
configure variables (in italics, see section above). 
Further search paths are determined by environment 
variables during runtime. 
The paths searched when 
running the compiler are as follows (the first catch wins):


1. Binary files (preprocessor, assembler and linker)


+-----------------------------------+--------------------+-------------------+
| 

Search path                     | 

default          | 

Win32 builds    |
+-----------------------------------+--------------------+-------------------+
+-----------------------------------+--------------------+-------------------+
| 

$SDCC_HOME/$PPREFIX2BIN_DIR     | 

$SDCC_HOME/bin   | 

$SDCC_HOME\bin  |
+-----------------------------------+--------------------+-------------------+
| 

Path of argv[0] (if available)  | 

Path of argv[0]  | 

Path of argv[0] |
+-----------------------------------+--------------------+-------------------+
| 

$PATH                           | 

$PATH            | 

$PATH           |
+-----------------------------------+--------------------+-------------------+

 


2. Include files


+------------------------------------------------------+--------------------------------------------------------------------------+----------------------------+
| 

Search path                                        | 

default                                                                | 

Win32 builds             |
+------------------------------------------------------+--------------------------------------------------------------------------+----------------------------+
+------------------------------------------------------+--------------------------------------------------------------------------+----------------------------+
| 

--I dir                                            | 

--I dir                                                                | 

--I dir                  |
+------------------------------------------------------+--------------------------------------------------------------------------+----------------------------+
| 

$SDCC_INCLUDE                                      | 

$SDCC_INCLUDE                                                          | 

$SDCC_INCLUDE            |
+------------------------------------------------------+--------------------------------------------------------------------------+----------------------------+
| 

$SDCC_HOME/
$PREFIX2DATA_DIR/
$INCLUDE_DIR_SUFFIX  | 

$SDCC_ HOME/
share/sdcc/
include                                       | 

$SDCC_HOME\include       |
+------------------------------------------------------+--------------------------------------------------------------------------+----------------------------+
| 

path(argv[0])/
$BIN2DATADIR/
$INCLUDE_DIR_SUFFIX   | 

path(argv[0])/
../sdcc/include
                                        | 

path(argv[0])\..\include |
+------------------------------------------------------+--------------------------------------------------------------------------+----------------------------+
| 

$DATADIR/
$INCLUDE_DIR_SUFFIX                      | 

/usr/local/share/sdcc/
include                                         | 

(not on Win32)           |
+------------------------------------------------------+--------------------------------------------------------------------------+----------------------------+

 


The option --nostdinc disables the last two search paths.


3. Library files 


With the exception of "--L dir" the model is 
auto-appended by the compiler (e.g. small, large, z80, 
ds390 etc.). 


+----------------------------------------------------------+-------------------------------------------------------------------------------+---------------------------------------------------------------------+
| 

Search path                                            | 

default                                                                     | 

Win32 builds                                                      |
+----------------------------------------------------------+-------------------------------------------------------------------------------+---------------------------------------------------------------------+
+----------------------------------------------------------+-------------------------------------------------------------------------------+---------------------------------------------------------------------+
| 

--L dir                                                | 

--L dir                                                                     | 

--L dir                                                           |
+----------------------------------------------------------+-------------------------------------------------------------------------------+---------------------------------------------------------------------+
| 

$SDCC_LIB/
<model>                                     | 

$SDCC_LIB/
<model>                                                          | 

$SDCC_LIB\
<model>                                                |
+----------------------------------------------------------+-------------------------------------------------------------------------------+---------------------------------------------------------------------+
| 

$SDCC_HOME/
$PREFIX2DATA_DIR/
$LIB_DIR_SUFFIX/<model>  | 

$SDCC_HOME/
share/sdcc/
lib/<model>                                         | 

$SDCC_HOME\lib\
<model>                                           |
+----------------------------------------------------------+-------------------------------------------------------------------------------+---------------------------------------------------------------------+
| 

path(argv[0])/
$BIN2DATADIR/
$LIB_DIR_SUFFIX/<model>   | 

path(argv[0])/
../sdcc/lib/<model>
                                         | 

path(argv[0])\
..\lib\<model>
                                    |
+----------------------------------------------------------+-------------------------------------------------------------------------------+---------------------------------------------------------------------+
| 

$DATADIR/
$LIB_DIR_SUFFIX/<model>                      | 

/usr/local/share/sdcc/
lib/<model>                                          | 

(not on Win32)                                                    |
+----------------------------------------------------------+-------------------------------------------------------------------------------+---------------------------------------------------------------------+





 
The option --nostdlib disables the last two search paths.

2.4 Building SDCC

2.4.1 Building SDCC on Linux<sub:Building-SDCC-on-Linux>

1. Download the source package either from the SDCC 
  Subversion repository or from snapshot builds, it 
  will be named something like 
  sdcc-src-yyyymmdd-rrrr.tar.bz2 [http://sdcc.sourceforge.net/snap.php].

2. Bring up a command line terminal, such as xterm.

3. Unpack the file using a command like: "tar -xvzf 
  sdcc-src-yyyymmdd-rrrr.tar.bz2", this will create a 
  sub-directory called sdcc with all of the sources.

4. Change directory into the main SDCC directory, for 
  example type: "cd sdcc".

5. Type "./configure". This configures the package for 
  compilation on your system.

6. Type "make". All of the source packages will 
  compile, this can take a while.

7. Type "make install" as root. This copies the binary 
  executables, the include files, the libraries and the 
  documentation to the install directories. Proceed 
  with section [sec:Testing-the-SDCC].

2.4.2 Building SDCC on Mac OS X

Follow the instruction for Linux.

On Mac OS X 10.2.x it 
was reported, that the default gcc (version 3.1 
20020420 (prerelease)) fails to compile SDCC. 
Fortunately there's also gcc 2.9.x installed, which 
works fine. This compiler can be selected by running 
'configure' with:

./configure CC=gcc2 CXX=g++2

Universal (ppc and i386) binaries can be produced on 
Mac OS X 10.4.x with Xcode. Run 'configure' with:

./configure \


LDFLAGS="-Wl,-syslibroot,/Developer/SDKs/MacOSX10.4u.sdk 
-arch i386 -arch ppc" \

CXXFLAGS = "-O2 -isysroot 
/Developer/SDKs/MacOSX10.4u.sdk -arch i386 -arch ppc" \

CFLAGS = "-O2 -isysroot /Developer/SDKs/MacOSX10.4u.sdk 
-arch i386 -arch ppc"

2.4.3 Cross compiling SDCC on Linux for Windows

With the Mingw32 gcc cross compiler it's easy to 
compile SDCC for Win32. See section 'Configure Options'.

2.4.4 Building SDCC using Cygwin and Mingw32

For building and installing a Cygwin executable follow 
the instructions for Linux.

On Cygwin a "native" 
Win32-binary can be built, which will not need the 
Cygwin-DLL. For the necessary 'configure' options see 
section 'configure options' or the script 
'sdcc/support/scripts/sdcc_cygwin_mingw32'.

In order to 
install Cygwin on Windows download setup.exe from [http://www.cygwin.com/||www.cygwin.com]. Run 
it, set the "default text file type" to "unix" and 
download/install at least the following packages. Some 
packages are selected by default, others will be 
automatically selected because of dependencies with the 
manually selected packages. Never deselect these packages!

* flex

* bison

* gcc ; version 3.x is fine, no need to use the old 2.9x

* binutils ; selected with gcc

* make

* rxvt ; a nice console, which makes life much easier 
  under windoze (see below)

* man ; not really needed for building SDCC, but you'll 
  miss it sooner or later

* less ; not really needed for building SDCC, but 
  you'll miss it sooner or later

* svn ; only if you use Subversion access

If you want to develop something you'll need:

* python ; for the regression tests

* gdb ; the gnu debugger, together with the nice GUI "insight"

* openssh ; to access the CF or commit changes

* autoconf and autoconf-devel ; if you want to fight 
  with 'configure', don't use autoconf-stable!

rxvt is a nice console with history. Replace in your 
cygwin.bat the line

bash --login -i 

with (one line):

rxvt -sl 1000 -fn "Lucida Console-12" -sr -cr red

     -bg black -fg white -geometry 100x65 -e bash --login

Text selected with the mouse is automatically copied to 
the clipboard, pasting works with shift-insert.

The 
other good tip is to make sure you have no //c/-style 
paths anywhere, use /cygdrive/c/ instead. Using // 
invokes a network lookup which is very slow. If you 
think "cygdrive" is too long, you can change it with e.g.

mount -s -u -c /mnt

SDCC sources use the unix line ending LF. Life is much 
easier, if you store the source tree on a drive which 
is mounted in binary mode. And use an editor which can 
handle LF-only line endings. Make sure not to commit 
files with windows line endings. The tabulator spacing 
used in the project is 8. Although a tabulator spacing 
of 8 is a sensible choice for programmers (it's a power 
of 2 and allows to display 8/16 bit signed variables 
without loosing columns) the plan is to move towards 
using only spaces in the source.

2.4.5 Building SDCC Using Microsoft Visual C++ 6.0/NET (MSVC)

Download the source package either from the SDCC 
Subversion repository or from the [http://sdcc.sourceforge.net/snap.php||snapshot builds], it will be named 
something like sdcc-src-yyyymmdd-rrrr.tar.bz2. SDCC is 
distributed with all the projects, workspaces, and 
files you need to build it using Visual C++ 6.0/NET 
(except for SDCDB and ucSim). The workspace name is 
'sdcc.dsw'. Please note that as it is now, all the 
executables are created in a folder called sdcc\bin_vc. 
Once built you need to copy the executables from 
sdcc\bin_vc to sdcc\bin before running SDCC. 

WARNING: 
Visual studio is very picky with line terminations; it 
expects the 0x0d, 0x0a DOS style line endings, not the 
0x0a Unix style line endings. When using the Subversion 
repository it's easiest to configure the svn client to 
convert automatically for you. If however you are 
getting a message such as "This makefile was not 
generated by Developer Studio etc. etc." when opening 
the sdcc.dsw workspace or any of the *.dsp projects, 
then you need to convert the Unix style line endings to 
DOS style line endings. To do so you can use the "unix2dos"
 utility freely available on the internet. Doug Hawkins 
reported in the sdcc-user list that this works:


C:\Programming\SDCC> unix2dos sdcc.dsw

C:\Programming\SDCC> for /R %I in (*.dsp) do @unix2dos "%I"


In order to build SDCC with MSVC you need win32 
executables of bison.exe, flex.exe, and gawk.exe. One 
good place to get them is [http://unxutils.sourceforge.net||here]

Download the file UnxUtils
.zip. Now you have to install the utilities and setup 
MSVC so it can locate the required programs. Here there 
are two alternatives (choose one!):

1. The easy way:

a) Extract UnxUtils.zip to your C:\ 
  hard disk PRESERVING the original paths, otherwise 
  bison won't work. (If you are using WinZip make 
  certain that 'Use folder names' is selected)

b) In the 
  Visual C++ IDE click Tools, Options, select the 
  Directory tab, in 'Show directories for:' select 
  'Executable files', and in the directories window add 
  a new path: 'C:\user\local\wbin', click ok.

(As a side 
  effect, you get a bunch of Unix utilities that could 
  be useful, such as diff and patch.)

2. A more compact way:

This one avoids extracting a 
  bunch of files you may not use, but requires some 
  extra work:

a) Create a directory were to put the 
  tools needed, or use a directory already present. Say 
  for example 'C:\util'.

b) Extract 'bison.exe', 
  'bison.hairy', 'bison.simple', 'flex.exe', and 
  gawk.exe to such directory WITHOUT preserving the 
  original paths. (If you are using WinZip make certain 
  that 'Use folder names' is not selected)

c) Rename 
  bison.exe to '_bison.exe'.

d) Create a batch file 
  'bison.bat' in 'C:\util\' and add these lines: 
  set 
  BISON_SIMPLE=C:\util\bison.simple 
  set 
  BISON_HAIRY=C:\util\bison.hairy
  _bison %1 %2 %3 %4 %5 
  %6 %7 %8 %9

Steps 'c' and 'd' are needed because bison 
  requires by default that the files 'bison.simple' and 
  'bison.hairy' reside in some weird Unix directory, 
  '/usr/local/share/' I think. So it is necessary to 
  tell bison where those files are located if they are 
  not in such directory. That is the function of the 
  environment variables BISON_SIMPLE and BISON_HAIRY.

e) 
  In the Visual C++ IDE click Tools, Options, select 
  the Directory tab, in 'Show directories for:' select 
  'Executable files', and in the directories window add 
  a new path: 'c:\util', click ok. Note that you can 
  use any other path instead of 'c:\util', even the 
  path where the Visual C++ tools are, probably: 
  'C:\Program Files\Microsoft Visual 
  Studio\Common\Tools'. So you don't have to execute 
  step 'e' :)

That is it. Open 'sdcc.dsw' in Visual Studio, click 
'build all', when it finishes copy the executables from 
sdcc\bin_vc to sdcc\bin, and you can compile using SDCC.

2.4.6 Building SDCC Using Borland

1. From the sdcc directory, run the command "make -f 
  Makefile.bcc". This should regenerate all the .exe 
  files in the bin directory except for SDCDB and ucSim.

2. If you modify any source files and need to rebuild, 
  be aware that the dependencies may not be correctly 
  calculated. The safest option is to delete all .obj 
  files and run the build again. From a Cygwin BASH 
  prompt, this can easily be done with the command (be 
  sure you are in the sdcc directory):

find . \( -name 
  '*.obj' -o -name '*.lib' -o -name '*.rul' \) -print 
  -exec rm {} \;

or on Windows NT/2000/XP from the 
  command prompt with the command:

del /s *.obj *.lib 
  *.rul from the sdcc directory.

2.4.7 Windows Install Using a ZIP Package

1. Download the binary zip package from [http://sdcc.sf.net/snap.php] and unpack it 
  using your favorite unpacking tool (gunzip, WinZip, 
  etc). This should unpack to a group of 
  sub-directories. An example directory structure after 
  unpacking the mingw32 package is: c:\sdcc\bin for the 
  executables, c:\sdcc\include and c:\sdcc\lib for the 
  include and libraries.

2. Adjust your environment variable PATH to include the 
  location of the bin directory or start sdcc using the 
  full path.

2.4.8 Windows Install Using the Setup Program<sub:Windows-Install>

Download the setup program sdcc-x.y.z-setup.exe for an 
official release from 
[http://sf.net/project/showfiles.php?group_id=599] or a setup program for one of 
the snapshots sdcc-yyyymmdd-xxxx-setup.exe from [http://sdcc.sf.net/snap.php] and 
execute it. A windows typical installer will guide you 
through the installation process.

2.4.9 VPATH feature

SDCC supports the VPATH feature provided by configure 
and make. It allows to separate the source and build 
trees. Here's an example:

cd ~                     # cd $HOME

tar -xzf sdcc.src.tar.gz # extract source to directory sdcc

mkdir sdcc.build         # put output in sdcc.build

cd sdcc.build

../sdcc/configure        # configure is doing all the magic!

make

That's it! configure will create the directory tree 
will all the necessary Makefiles in ~/sdcc.build. It 
automagically computes the variables srcdir, top_srcdir 
and top_buildir for each directory. After running make 
the generated files will be in ~/sdcc.build, while the 
source files stay in ~/sdcc.
This is not only usefull 
for building different binaries, e.g. when cross 
compiling. It also gives you a much better overview in 
the source tree when all the generated files are not 
scattered between the source files. And the best thing 
is: if you want to change a file you can leave the 
original file untouched in the source directory. Simply 
copy it to the build directory, edit it, enter `make 
clean', `rm Makefile.dep' and `make'. make will do the 
rest for you!

2.5 Building the Documentation

Add --enable-doc to the configure arguments to build 
the documentation together with all the other stuff. 
You will need several tools (LyX, LaTeX, LaTeX2HTML, 
pdflatex, dvipdf, dvips and makeindex) to get the job 
done. Another possibility is to change to the doc 
directory and to type "make" there. You're invited to 
make changes and additions to this manual 
(sdcc/doc/sdccman.lyx). Using LyX [http://www.lyx.org] as editor is 
straightforward. Prebuilt documentation in html and pdf 
format is available from [http://sdcc.sf.net/snap.php].

2.6 Reading the Documentation

Currently reading the document in pdf format is 
recommended, as for unknown reason the hyperlinks are 
working there whereas in the html version they are not

If you should know why please drop us a note
. 
You'll find the pdf version at [http://sdcc.sf.net/doc/sdccman.pdf]. 
A html version 
should be online at [http://sdcc.sf.net/doc/sdccman.html/index.html].
This documentation is in some 
aspects different from a commercial documentation: 

* It tries to document SDCC for several processor 
  architectures in one document (commercially these 
  probably would be separate documents/products). This document
   currently matches SDCC for mcs51 and DS390 best and 
  does give too few information about f.e. Z80, PIC14, 
  PIC16 and HC08.

* There are many references pointing away from this 
  documentation. Don't let this distract you. If there 
  f.e. was a reference like [http://www.opencores.org] together with a statement "
  some processors which are targetted by SDCC can be 
  implemented in a field programmable gate array" or [http://sf.net/projects/fpgac] "
  have you ever heard of an open source compiler that 
  compiles a subset of C for an FPGA?" we expect you to 
  have a quick look there and come back. If you read 
  this you are on the right track.

* Some sections attribute more space to problems, 
  restrictions and warnings than to the solution.

* The installation section and the section about the 
  debugger is intimidating.

* There are still lots of typos and there are more 
  different writing styles than pictures.

2.7 Testing the SDCC Compiler<sec:Testing-the-SDCC>

The first thing you should do after installing your 
SDCC compiler is to see if it runs. Type "sdcc --version"
 at the prompt, and the program should run and output 
its version like: 
SDCC : 
mcs51/z80/avr/ds390/pic16/pic14/ds400/hc08 2.5.6 #4169 
(May 8 2006) (UNIX)

If it doesn't run, or gives a message about not finding 
sdcc program, then you need to check over your 
installation. Make sure that the sdcc bin directory is 
in your executable search path defined by the PATH 
environment setting (see section [sub:Install-Trouble-shooting] Install 
trouble-shooting for suggestions). Make sure that the 
sdcc program is in the bin folder, if not perhaps 
something did not install correctly.

SDCC is commonly 
installed as described in section "Install and search paths".


Make sure the compiler works on a very simple example. 
Type in the following test.c program using your 
favorite ASCII editor:

char test;

void main(void) {
    test=0;
}

Compile this using the following command: "sdcc -c 
test.c". If all goes well, the compiler will generate a 
test.asm and test.rel file. Congratulations, you've 
just compiled your first program with SDCC. We used the 
-c option to tell SDCC not to link the generated code, 
just to keep things simple for this step.

The next step 
is to try it with the linker. Type in "sdcc test.c". If 
all goes well the compiler will link with the libraries 
and produce a test.ihx output file. If this step fails 
(no test.ihx, and the linker generates warnings), then 
the problem is most likely that SDCC cannot find the 
/usr/local/share/sdcc/lib directory (see section [sub:Install-Trouble-shooting] 
Install trouble-shooting for suggestions).

The final 
test is to ensure SDCC can use the standard header 
files and libraries. Edit test.c and change it to the following:

#include <string.h>

char str1[10];

void main(void) {
  
strcpy(str1, "testing");
}

Compile this by typing "sdcc test.c". This should 
generate a test.ihx output file, and it should give no 
warnings such as not finding the string.h file. If it 
cannot find the string.h file, then the problem is that 
SDCC cannot find the /usr/local/share/sdcc/include 
directory (see the section [sub:Install-Trouble-shooting] Install trouble-shooting 
section for suggestions). Use option --print-search-dirs
 to find exactly where SDCC is looking for the include 
and lib files.

2.8 Install Trouble-shooting<sub:Install-Trouble-shooting>

2.8.1 If SDCC does not build correctly

A thing to try is starting from scratch by unpacking 
the .tgz source package again in an empty directory. 
Configure it like:

./configure 2>&1 | tee configure.log


and build it like:

make 2>&1 | tee make.log

If anything 
goes wrong, you can review the log files to locate the 
problem. Or a relevant part of this can be attached to 
an email that could be helpful when requesting help 
from the mailing list.

2.8.2 What the "./configure" does

The "./configure" command is a script that analyzes your 
system and performs some configuration to ensure the 
source package compiles on your system. It will take a 
few minutes to run, and will compile a few tests to 
determine what compiler features are installed.

2.8.3 What the "make" does

This runs the GNU make tool, which automatically 
compiles all the source packages into the final 
installed binary executables.

2.8.4 What the "make install" command does.

This will install the compiler, other executables 
libraries and include files into the appropriate 
directories. See sections [sub:Install-paths], [sub:Search-Paths] about install and search paths.

On most systems you will need super-user privileges to 
do this.

2.9 Components of SDCC

SDCC is not just a compiler, but a collection of tools 
by various developers. These include linkers, 
assemblers, simulators and other components. Here is a 
summary of some of the components. Note that the 
included simulator and assembler have separate 
documentation which you can find in the source package 
in their respective directories. As SDCC grows to 
include support for other processors, other packages 
from various developers are included and may have their 
own sets of documentation.

You might want to look at the 
files which are installed in <installdir>. At the time 
of this writing, we find the following programs for gcc-builds:

 
In <installdir>/bin:

* sdcc - The compiler.

* sdcpp - The C preprocessor.

* asx8051 - The assembler for 8051 type processors.

* as-z80, as-gbz80 - The Z80 and GameBoy Z80 assemblers.

* aslink -The linker for 8051 type processors.

* link-z80, link-gbz80 - The Z80 and GameBoy Z80 linkers.

* s51 - The ucSim 8051 simulator.

* sdcdb - The source debugger.

* packihx - A tool to pack (compress) Intel hex files.

In <installdir>/share/sdcc/include

* the include files

In <installdir>/share/sdcc/lib

* the subdirs src and small, large, z80, gbz80 and 
  ds390 with the precompiled relocatables.

In <installdir>/share/sdcc/doc

* the documentation

As development for other processors proceeds, this list 
will expand to include executables to support 
processors like AVR, PIC, etc.

2.9.1 sdcc - The Compiler

This is the actual compiler, it in turn uses the 
c-preprocessor and invokes the assembler and linkage editor.

2.9.2 sdcpp - The C-Preprocessor

The preprocessor is a modified version of the GNU cpp 
preprocessor [http://gcc.gnu.org/]. The C preprocessor is used to pull in 
#include sources, process #ifdef statements, #defines 
and so on.

2.9.3 asxxxx, aslink, link-xxx - The Assemblers and 
  Linkage Editors

This is retargettable assembler & linkage editor, it 
was developed by Alan Baldwin. John Hartman created the 
version for 8051, and I (Sandeep) have made some 
enhancements and bug fixes for it to work properly with SDCC.

2.9.4 s51 - The Simulator

S51 is a free open source simulator developed by Daniel 
Drotos. The simulator is built as part of the build 
process. For more information visit Daniel's web site 
at: [http://mazsola.iit.uni-miskolc.hu/~drdani/embedded/s51]. It currently supports the core mcs51, the Dallas 
DS80C390 and the Phillips XA51 family.

2.9.5 sdcdb - Source Level Debugger

SDCDB is the companion source level debugger. More 
about SDCDB in section [cha:Debugging-with-SDCDB]. The current version of the 
debugger uses Daniel's Simulator S51, but can be easily 
changed to use other simulators.

Using SDCC

3.1 Compiling

3.1.1 Single Source File Projects

For single source file 8051 projects the process is 
very simple. Compile your programs with the following 
command "sdcc sourcefile.c". This will compile, 
assemble and link your source file. Output files are as follows:

* sourcefile.asm - Assembler source file created by the compiler

* sourcefile.lst - Assembler listing file created by 
  the Assembler

* sourcefile.rst - Assembler listing file updated with 
  linkedit information, created by linkage editor

* sourcefile.sym - symbol listing for the sourcefile, 
  created by the assembler

* sourcefile.rel or sourcefile.o - Object file created 
  by the assembler, input to Linkage editor

* sourcefile.map - The memory map for the load module, 
  created by the Linker

* sourcefile.mem - A file with a summary of the memory usage

* sourcefile.ihx - The load module in Intel hex format 
  (you can select the Motorola S19 format with --out-fmt-s19
  . If you need another format you might want to use objdump
   or srecord - see also section [sub:Postprocessing-the-Intel]). Both formats are 
  documented in the documentation of srecord

* sourcefile.adb - An intermediate file containing 
  debug information needed to create the .cdb file 
  (with --debug) 

* sourcefile.cdb - An optional file (with --debug) 
  containing debug information. The format is 
  documented in cdbfileformat.pdf

* sourcefile. - (no extension) An optional AOMF or AOMF51
   <OMF file>file containing debug information (generated with 
  option --debug). The (Intel) absolute object module 
  format is a subformat of the OMF51 format and is 
  commonly used by third party tools (debuggers, 
  simulators, emulators).

* sourcefile.dump* - Dump file to debug the compiler it 
  self (generated with option --dumpall) (see section [sub:Intermediate-Dump-Options]  
  and section [sub:The-anatomy-of] "Anatomy of the compiler").

3.1.2 Postprocessing the Intel Hex file<sub:Postprocessing-the-Intel>

In most cases this won't be needed but the Intel Hex file
 which is generated by SDCC might include lines of 
varying length and the addresses within the file are 
not guaranteed to be strictly ascending. If your 
toolchain or a bootloader does not like this you can 
use the tool packihx which is part of the SDCC 
distribution: 

 packihx sourcefile.ihx >sourcefile.hex


The separately available srecord package additionally 
allows to set undefined locations to a predefined 
value, to insert checksums of various flavours (crc, 
add, xor) and to perform other manipulations (convert, 
split, crop, offset, ...). 

srec_cat  sourcefile.ihx -intel  
-o sourcefile.hex -intel

An example for a more complex 
command line

the command backfills unused memory with 0x12 and the 
overall 16 bit sum of the complete 64 kByte block is 
zero. If the program counter on an mcs51 runs wild the 
backfill pattern 0x12 will be interpreted as an lcall 
to address 0x1212 (where an emergency routine could sit).
 could look like:

srec_cat sourcefile.ihx -intel  -fill 
0x12 0x0000 0xfffe -little-endian-checksum-negative 
0xfffe 0x02 0x02  -o sourcefile.hex -intel

The srecord 
package is available at [http://sf.net/projects/srecord] .

3.1.3 Projects with Multiple Source Files

SDCC can compile only ONE file at a time. Let us for 
example assume that you have a project containing the 
following files:

foo1.c (contains some functions)
foo2.c 
(contains some more functions)
foomain.c (contains more 
functions and the function main)

The first two files 
will need to be compiled separately with the commands: 

sdcc -c 
foo1.c
sdcc -c foo2.c

Then compile the source file 
containing the main() function and link the files 
together with the following command: 

sdcc foomain.c foo1.rel 
foo2.rel

Alternatively, foomain.c can be separately 
compiled as well: 

sdcc -c foomain.c
sdcc foomain.rel 
foo1.rel foo2.rel

The file containing the main() 
function must be the first file specified in the 
command line, since the linkage editor processes file 
in the order they are presented to it. The linker is 
invoked from SDCC using a script file with extension .lnk
. You can view this file to troubleshoot linking 
problems such as those arising from missing libraries.

3.1.4 Projects with Additional Libraries

Some reusable routines may be compiled into a library, 
see the documentation for the assembler and linkage 
editor (which are in <installdir>/share/sdcc/doc) for 
how to create a .lib library file. Libraries created in 
this manner can be included in the command line. Make 
sure you include the -L <library-path> option to tell 
the linker where to look for these files if they are 
not in the current directory. Here is an example, 
assuming you have the source file foomain.c and a 
library foolib.lib in the directory mylib (if that is 
not the same as your current project):

sdcc foomain.c 
foolib.lib -L mylib

Note here that mylib must be an 
absolute path name.

The most efficient way to use 
libraries is to keep separate modules in separate 
source files. The lib file now should name all the modules.rel
 files. For an example see the standard library file 
libsdcc.lib in the directory <installdir>/share/lib/small.

3.1.5 Using sdcclib to Create and Manage Libraries

Alternatively, instead of having a .rel file for each 
entry on the library file as described in the preceding 
section, sdcclib can be used to embed all the modules 
belonging to such library in the library file itself. 
This results in a larger library file, but it greatly 
reduces the number of disk files accessed by the 
linker.  Additionally, the packed library file contains 
an index of all include modules and symbols that 
significantly speeds up the linking process. To display 
a list of options supported by sdcclib type:


sdcclib -?

To create a new library file, start by 
compiling all the required modules. For example:


sdcc -c _divsint.c

sdcc -c _divuint.c

sdcc -c _modsint.c

sdcc -c _moduint.c

sdcc -c _mulint.c


This will create files _divsint.rel, _divuint.rel, 
_modsint.rel, _moduint.rel, and _mulint.rel. The next 
step is to add the .rel files to the library file:


sdcclib libint.lib _divsint.rel

sdcclib libint.lib _divuint.rel

sdcclib libint.lib _modsint.rel

sdcclib libint.lib _moduint.rel

sdcclib libint.lib _mulint.rel


Or, if you preffer:


sdcclib libint.lib _divsint.rel _divuint.rel 
_modsint.rel _moduint.rel _mulint.rel


If the file already exists in the library, it will be 
replaced. If a list of .rel files is available, you can 
tell sdcclib to add those files to a library. For 
example, if the file 'myliblist.txt' contains


_divsint.rel

_divuint.rel

_modsint.rel

_moduint.rel

_mulint.rel


Use


sdcclib -l libint.lib myliblist.txt


Additionally, you can instruct sdcclib to compiles the 
files before adding them to the library. This is 
achieved using the environment variables SDCCLIB_CC 
and/or SDCCLIB_AS. For example:


set SDCCLIB_CC=sdcc -c

sdcclib -l libint.lib myliblist.txt


To see what modules and symbols are included in the 
library, options -s and -m are available. For example:


sdcclib -s libint.lib
_divsint.rel:

__divsint_a_1_1

__divsint_PARM_2

__divsint
_divuint.rel:

__divuint_a_1_1

__divuint_PARM_2

__divuint_reste_1_1

__divuint_count_1_1

__divuint
_modsint.rel:

__modsint_a_1_1

__modsint_PARM_2

__modsint
_moduint.rel:

__moduint_a_1_1

__moduint_PARM_2

__moduint_count_1_1

__moduint
_mulint.rel:

__mulint_PARM_2

__mulint


If the source files are compiled using --debug, the 
corresponding debug information file .adb will be 
include in the library file as well. The library files 
created with sdcclib are plain text files, so they can 
be viewed with a text editor. It is not recomended to 
modify a library file created with sdcclib using a text 
editor, as there are file indexes numbers located 
accross the file used by the linker to quickly locate 
the required module to link. Once a .rel file (as well 
as a .adb file) is added to a library using sdcclib, it 
can be safely deleted, since all the information 
required for linking is embedded in the library file 
itself. Library files created using sdcclib are used as 
described in the preceding sections.



3.2 Command Line Options<sec:Command-Line-Options>

3.2.1 Processor Selection Options

-mmcs51 Generate code for the Intel MCS51 family of 
processors. This is the default processor target.

-mds390 Generate code for the Dallas DS80C390 processor.

-mds400 Generate code for the Dallas DS80C400 processor.

-mhc08 Generate code for the Freescale/Motorola HC08 
family of processors.

-mz80 Generate code for the Zilog Z80 family of processors.

-mgbz80 Generate code for the GameBoy Z80 processor 
(Not actively maintained).

-mavr Generate code for the Atmel AVR processor (Not 
maintained, not complete). AVR users should probably 
have a look at winavr [http://sourceforge.net/projects/winavr] or [http://www.avrfreaks.net/index.php?name=PNphpBB2&file=index], which is based on AVR-port 
of the gcc compiler.



-mpic14 Generate code for the Microchip PIC 14-bit 
processors (p16f84 and variants. In development, not complete).



-mpic16 Generate code for the Microchip PIC 16-bit 
processors (p18f452 and variants. In development, not complete).

-mtlcs900h Generate code for the Toshiba TLCS-900H 
processor (Not maintained, not complete).

-mxa51 Generate code for the Phillips XA51 processor 
(Not maintained, not complete).





3.2.2 Preprocessor Options

-I<path> The additional location where the preprocessor 
will look for <..h> or "..h" files.

-D<macro[=value]> Command line definition of macros. 
Passed to the preprocessor.

-M Tell the preprocessor to output a rule suitable for 
make describing the dependencies of each object file. 
For each source file, the preprocessor outputs one 
make-rule whose target is the object file name for that 
source file and whose dependencies are all the files 
`#include'd in it. This rule may be a single line or 
may be continued with `\'-newline if it is long. The 
list of rules is printed on standard output instead of 
the preprocessed C program. `-M' implies `-E'.

-C Tell the preprocessor not to discard comments. Used 
with the `-E' option.

-MM Like `-M' but the output mentions only the user 
header files included with `#include "file"'. System 
header files included with `#include <file>' are omitted.

-Aquestion(answer) Assert the answer answer for 
question, in case it is tested with a preprocessor 
conditional such as `#if #question(answer)'. `-A-' 
disables the standard assertions that normally describe 
the target machine.

-Umacro Undefine macro macro. `-U' options are 
evaluated after all `-D' options, but before any 
`-include' and `-imacros' options.

-dM Tell the preprocessor to output only a list of the 
macro definitions that are in effect at the end of 
preprocessing. Used with the `-E' option.

-dD Tell the preprocessor to pass all macro definitions 
into the output, in their proper sequence in the rest 
of the output.

-dN Like `-dD' except that the macro arguments and 
contents are omitted. Only `#define name' is included 
in the output.

-pedantic-parse-number<lyx:-pedantic-parse-number> Pedantic parse numbers so that 
situations like 0xfe-LO_B(3) are parsed properly and 
the macro LO_B(3) gets expanded. See also #pragma 
pedantic_parse_number [ite:pedantic_parse_number] in section[sec:Pragmas] Note: this 
functionality is not in conformance with C99 standard!

-Wp preprocessorOption[,preprocessorOption]... Pass the 
preprocessorOption to the preprocessor sdcpp. SDCC uses 
an adapted version of the preprocessor cpp of the GNU 
Compiler Collection (gcc [http://gcc.gnu.org/]), if you need more dedicated 
options please refer to the GCC 4.1.1 CPP Manual at [http://www.gnu.org/software/gcc/onlinedocs/].





3.2.3 Linker Options

-L --lib-path <absolute path to additional libraries> 
This option is passed to the linkage editor's 
additional libraries search path. The path name must be 
absolute. Additional library files may be specified in 
the command line. See section Compiling programs for 
more details.

--xram-loc <Value> The start location of the external ram
, default value is 0. The value entered can be in 
Hexadecimal or Decimal format, e.g.: --xram-loc 0x8000 
or --xram-loc 32768.

--code-loc <Value> The start location of the code 
segment, default value 0. Note when this option is used 
the interrupt vector table is also relocated to the 
given address. The value entered can be in Hexadecimal 
or Decimal format, e.g.: --code-loc 0x8000 or -
-code-loc 32768.

--stack-loc <Value> By default the stack is placed after 
the data segment. Using this option the stack can be 
placed anywhere in the internal memory space of the 
8051. The value entered can be in Hexadecimal or 
Decimal format, e.g. --stack-loc 0x20 or --stack-loc 
32. Since the sp register is incremented before a push 
or call, the initial sp will be set to one byte prior 
the provided value. The provided value should not 
overlap any other memory areas such as used register 
banks or the data segment and with enough space for the 
current application. The --pack-iram  option (which is 
now a default setting) will override this setting, so 
you should also specify the --no-pack-iram  option if 
you need to manually place the stack.

--xstack-loc <Value> By default the external stack is 
placed after the pdata segment. Using this option the 
xstack can be placed anywhere in the external memory 
space of the 8051. The value entered can be in 
Hexadecimal or Decimal format, e.g. --xstack-loc 0x8000 
or --stack-loc 32768. The provided value should not 
overlap any other memory areas such as the pdata or 
xdata segment and with enough space for the current application.

--data-loc <Value> The start location of the internal 
ram data segment. The value entered can be in 
Hexadecimal or Decimal format, eg. --data-loc 0x20 or -
-data-loc 32. (By default, the start location of the 
internal ram data segment  is set as low as possible in 
memory, taking into account the used register banks and 
the bit segment at address 0x20. For example if 
register banks 0 and 1 are used without bit variables, 
the data segment will be set, if --data-loc is not 
used, to location 0x10.)

--idata-loc <Value> The start location of the indirectly 
addressable internal ram of the 8051, default value is 
0x80. The value entered can be in Hexadecimal or 
Decimal format, eg. --idata-loc 0x88 or --idata-loc 136.

--bit-loc <Value> The start location of the bit 
addressable internal ram of the 8051. This is not 
implemented yet. Instead an option can be passed 
directly to the linker: -Wl -bBSEG=<Value>.

--out-fmt-ihx The linker output (final object code) is 
in Intel Hex format. This is the default option. The 
format itself is documented in the documentation of srecord.

--out-fmt-s19 The linker output (final object code) is 
in Motorola S19 format. The format itself is documented 
in the documentation of srecord.

--out-fmt-elf The linker output (final object code) is 
in ELF format. (Currently only supported for the HC08 processors)

-Wl linkOption[,linkOption]<lyx:-Wl option>... Pass the linkOption to 
the linker. If a bootloader is used an option like "-Wl 
-bCSEG=0x1000" would be typical to set the start of the 
code segment. Either use the double quotes around this 
option or use no space (e.g. -Wl-bCSEG=0x1000). See 
also #pragma constseg and #pragma codeseg in section [sec:Pragmas] . 
File sdcc/as/doc/asxhtm.html has more on linker options.





3.2.4 MCS51 Options

--model-small Generate code for Small Model programs, 
see section Memory Models for more details. This is the 
default model.

--model-medium Generate code for Medium model programs, 
see section Memory Models for more details. If this 
option is used all source files in the project have to 
be compiled with this option. It must also be used when 
invoking the linker.

--model-large Generate code for Large model programs, 
see section Memory Models for more details. If this 
option is used all source files in the project have to 
be compiled with this option. It must also be used when 
invoking the linker.

--xstack Uses a pseudo stack in the pdata area (usually 
the first 256 bytes in the external ram) for allocating 
variables and passing parameters. See section [sub:External-Stack]  External 
Stack for more details.

--iram-size <Value> Causes the linker to check if the 
internal ram usage is within limits of the given value.

--xram-size <Value> Causes the linker to check if the 
external ram usage is within limits of the given value.

--code-size <Value> Causes the linker to check if the 
code memory usage is within limits of the given value.

--stack-size <Value> Causes the linker to check if there 
is at minimum <Value> bytes for stack.

--pack-iram  Causes the linker to use unused register 
banks for data variables and pack data, idata and stack 
together. This is the default now.

--no-pack-iram  Causes the linker to use old style for 
allocating memory areas.

--acall-ajmp  Replaces the three byte instructions 
lcall/ljmp with the two byte instructions acall/ajmp. 
Only use this option if your code is in the same 2k 
block of memory. You may need to use this option for 
some 8051 derivatives which lack the lcall/ljmp instructions..





3.2.5 DS390 / DS400 Options

--model-flat24 Generate 24-bit flat mode code. This is 
the one and only that the ds390 code generator supports 
right now and is default when using -mds390. See 
section Memory Models for more details.

--protect-sp-update disable interrupts during ESP:SP updates.

--stack-10bit Generate code for the 10 bit stack mode 
of the Dallas DS80C390 part. This is the one and only 
that the ds390 code generator supports right now and is 
default when using -mds390. In this mode, the stack is 
located in the lower 1K of the internal RAM, which is 
mapped to 0x400000. Note that the support is 
incomplete, since it still uses a single byte as the 
stack pointer. This means that only the lower 256 bytes 
of the potential 1K stack space will actually be used. 
However, this does allow you to reclaim the precious 
256 bytes of low RAM for use for the DATA and IDATA 
segments. The compiler will not generate any code to 
put the processor into 10 bit stack mode. It is 
important to ensure that the processor is in this mode 
before calling any re-entrant functions compiled with 
this option. In principle, this should work with the --stack-auto
 option, but that has not been tested. It is 
incompatible with the --xstack option. It also only 
makes sense if the processor is in 24 bit contiguous 
addressing mode (see the --model-flat24 option).

--stack-probe insert call to function __stack_probe at 
each function prologue.

--tini-libid <nnnn> LibraryID used in -mTININative. 

--use-accelerator generate code for DS390 Arithmetic 
Accelerator. 





3.2.6 Z80 Options

--callee-saves-bc Force a called function to always 
save BC.

--no-std-crt0 When linking, skip the standard crt0.o 
object file. You must provide your own crt0.o for your 
system when linking.

--portmode=<Value> Determinate PORT I/O mode (<Value> 
is z80 or z180).

--asm=<Value> Define assembler name (<Value> is rgbds, 
asxxxx, isas or z80asm).

--codeseg <Value> Use <Value> for the code segment name.

--constseg <Value> Use <Value> for the const segment name.





3.2.7 GBZ80 Options

--callee-saves-bc Force a called function to always 
save BC.

--no-std-crt0 When linking, skip the standard crt0.o 
object file. You must provide your own crt0.o for your 
system when linking.

-bo <Num> Use code bank <Num>.

-ba <Num> Use data bank <Num>.

--codeseg <Value> Use <Value> for the code segment name.

--constseg <Value> Use <Value> for the const segment name.





3.2.8 Optimization Options

--nogcse Will not do global subexpression elimination, 
this option may be used when the compiler creates 
undesirably large stack/data spaces to store compiler 
temporaries (spill locations, sloc). A warning message 
will be generated when this happens and the compiler 
will indicate the number of extra bytes it allocated. 
It is recommended that this option NOT be used, #pragma nogcse
 can be used to turn off global subexpression elimination
 for a given function only.

--noinvariant Will not do loop invariant optimizations, 
this may be turned off for reasons explained for the 
previous option. For more details of loop optimizations 
performed see Loop Invariants in section [sub:Loop-Optimizations]. It is 
recommended that this option NOT be used, #pragma noinvariant
 can be used to turn off invariant optimizations for a 
given function only.

--noinduction Will not do loop induction optimizations, 
see section strength reduction for more details. It is 
recommended that this option is NOT used, #pragma noinduction
 can be used to turn off induction optimizations for a 
given function only.

--nojtbound  Will not generate boundary condition check 
when switch statements are implemented using 
jump-tables. See section [sub:'switch'-Statements] Switch Statements for more 
details. It is recommended that this option is NOT 
used, #pragma nojtbound can be used to turn off boundary 
checking for jump tables for a given function only.

--noloopreverse Will not do loop reversal optimization.

--nolabelopt Will not optimize labels (makes the 
dumpfiles more readable).

--no-xinit-opt Will not memcpy initialized data from 
code space into xdata space. This saves a few bytes in 
code space if you don't have initialized data.

--nooverlay  The compiler will not overlay parameters 
and local variables of any function, see section 
Parameters and local variables for more details.

--no-peep Disable peep-hole optimization with built-in rules.

--peep-file <filename> This option can be used to use 
additional rules to be used by the peep hole optimizer. 
See section [sub:Peephole-Optimizer] Peep Hole optimizations for details on how 
to write these rules.

--peep-asm Pass the inline assembler code through the 
peep hole optimizer. This can cause unexpected changes 
to inline assembler code, please go through the 
peephole optimizer rules defined in the source file 
tree '<target>/peeph.def' before using this option.

--opt-code-speed The compiler will optimize code 
generation towards fast code, possibly at the expense 
of code size.

--opt-code-size The compiler will optimize code 
generation towards compact code, possibly at the 
expense of code speed.





3.2.9 Other Options

-c --compile-only will compile and assemble the source, 
but will not call the linkage editor.

--c1mode reads the preprocessed source from standard 
input and compiles it. The file name for the assembler 
output must be specified using the -o option.

-E Run only the C preprocessor. Preprocess all the C 
source files specified and output the results to 
standard output.

-o <path/file> The output path where everything will be 
placed or the file name used for all generated output 
files. If the parameter is a path, it must have a 
trailing slash (or backslash for the Windows binaries) 
to be recognized as a path. Note for Windows users: if 
the path contains spaces, it should be surrounded by 
quotes. The trailing backslash should be doubled in 
order to prevent escaping the final quote, for example: 
-o "F:\Projects\test3\output 1\\" or put after the final 
quote, for example: -o "F:\Projects\test3\output 1"\. The 
path using slashes for directory delimiters can be used 
too, for example: -o "F:/Projects/test3/output 1/".

--stack-auto All functions in the source file will be 
compiled as reentrant, i.e. the parameters and local 
variables will be allocated on the stack. See section [sec:Parameters-and-Local-Variables] 
Parameters and Local Variables for more details. If 
this option is used all source files in the project 
should be compiled with this option. It automatically 
implies --int-long-reent and --float-reent. 

--callee-saves <lyx:--callee-saves-function1[,function2][,function3]...>function1[,function2][,function3].... 
The compiler by default uses a caller saves convention 
for register saving across function calls, however this 
can cause unnecessary register pushing and popping when 
calling small functions from larger functions. This 
option can be used to switch the register saving 
convention for the function names specified. The 
compiler will not save registers when calling these 
functions, no extra code will be generated at the entry 
and exit (function prologue and epilogue) for these 
functions to save and restore the registers used by 
these functions, this can SUBSTANTIALLY reduce code and 
improve run time performance of the generated code. In 
the future the compiler (with inter procedural 
analysis) will be able to determine the appropriate 
scheme to use for each function call. DO NOT use this 
option for built-in functions such as _mulint..., if 
this option is used for a library function the 
appropriate library function needs to be recompiled 
with the same option. If the project consists of 
multiple source files then all the source file should 
be compiled with the same --callee-saves option string. 
Also see #pragma callee_saves  [ite:callee_saves-function1[,function2[,function3...]]--].

--all-callee-saves Function of --callee-saves will be 
applied to all functions by default.

--debug When this option is used the compiler will 
generate debug information. The debug information 
collected in a file with .cdb extension can be used 
with the SDCDB. For more information see documentation 
for SDCDB. Another file with no extension contains 
debug information in AOMF or AOMF51 format which is 
commonly used by third party tools.

-S Stop after the stage of compilation proper; do not 
assemble. The output is an assembler code file for the 
input file specified.

--int-long-reent Integer (16 bit) and long (32 bit) 
libraries have been compiled as reentrant. Note by 
default these libraries are compiled as non-reentrant. 
See section Installation for more details.

--cyclomatic This option will cause the compiler to 
generate an information message for each function in 
the source file. The message contains some important 
information about the function. The number of edges and 
nodes the compiler detected in the control flow graph 
of the function, and most importantly the cyclomatic complexity
 see section on Cyclomatic Complexity for more details.

--float-reent Floating point library is compiled as reentrant
. See section Installation for more details.

--funsigned-char The default signedness for every type 
is signed. In some embedded environments the default 
signedness of char is unsigned. To set the signess for 
characters to unsigned, use the option -
-funsigned-char. If this option is set and no 
signedness keyword (unsigned/signed) is given, a char 
will be signed. All other types are unaffected.

--main-return This option can be used if the code 
generated is called by a monitor program or if the main 
routine includes an endless loop. This option results 
in slightly smaller code and saves two bytes of stack 
space. The return from the 'main' function will return 
to the function calling main. The default setting is to 
lock up i.e. generate a 'sjmp .'.

--nostdinc This will prevent the compiler from passing 
on the default include path to the preprocessor.

--nostdlib This will prevent the compiler from passing 
on the default library path to the linker.

--verbose Shows the various actions the compiler is performing.

-V Shows the actual commands the compiler is executing.

--no-c-code-in-asm Hides your ugly and inefficient 
c-code from the asm file, so you can always blame the 
compiler :)

--fverbose-asm Include code generator and peep-hole 
comments in the generated asm files.

--no-peep-comments Don't include peep-hole comments in 
the generated asm files even if --fverbose-asm option 
is specified.

--i-code-in-asm Include i-codes in the asm file. Sounds 
like noise but is most helpful for debugging the 
compiler itself.

--less-pedantic<lyx:--less-pedantic> Disable some of the more pedantic warnings
. For more details, see the less_pedantic pragma [ite:less_pedantic].

--disable-warning <nnnn> Disable specific warning with 
number <nnnn>.

--Werror Treat all warnings as errors.

--print-search-dirs Display the directories in the 
compiler's search path

--vc Display errors and warnings using MSVC style, so 
you can use SDCC with the visual studio IDE. With SDCC 
both offering a GCC-like (the default) and a MSVC-like 
output style, integration into most programming editors 
should be straightforward.

--use-stdout Send errors and warnings to stdout instead 
of stderr.

-Wa asmOption[,asmOption]... Pass the asmOption to the assembler
. See file sdcc/as/doc/asxhtm.html for assembler options.cd

--std-sdcc89 Generally follow the C89 standard, but 
allow SDCC features that conflict with the standard (default).

--std-c89 Follow the C89 standard and disable SDCC 
features that conflict with the standard.

--std-sdcc99 Generally follow the C99 standard, but 
allow SDCC features that conflict with the standard 
(incomplete support).

--std-c99 Follow the C99 standard and disable SDCC 
features that conflict with the standard (incomplete support).

--codeseg<lyx:-codeseg> <Name> The name to be used for the code 
segment, default CSEG. This is useful if you need to 
tell the compiler to put the code in a special segment 
so you can later on tell the linker to put this segment 
in a special place in memory. Can be used for instance 
when using bank switching to put the code in a bank.

--constseg <Name> The name to be used for the const 
segment, default CONST. This is useful if you need to 
tell the compiler to put the const data in a special 
segment so you can later on tell the linker to put this 
segment in a special place in memory. Can be used for 
instance when using bank switching to put the const 
data in a bank.

--fdollars-in-identifiers Permit '$' as an identifier character.

--more-pedantic Actually this is not a SDCC compiler 
option but if you want more warnings you can use a 
separate tool dedicated to syntax checking like splint<lyx:more-pedantic-SPLINT> [http://www.splint.org]
. To make your source files parseable by splint you 
will have to include lint.h in your source file and add 
brackets around extended keywords (like "__at (0xab)" and "
__interrupt (2)"). 
Splint has an excellent on line manual 
at [http://www.splint.org/manual/] and it's capabilities go beyond pure syntax 
checking. You'll need to tell splint the location of 
SDCC's include files so a typical command line could 
look like this: 
splint -I /usr/local/share/sdcc/include/mcs51/  
myprogram.c

--short-is-8bits<lyx:--short-is-8bits> Treat short as 8-bit (for backward 
compatibility with older versions of compiler - see 
section [sec:Compatibility-with-previous])





3.2.10 Intermediate Dump Options<sub:Intermediate-Dump-Options>

The following options are provided for the purpose of 
retargetting and debugging the compiler. They provide a 
means to dump the intermediate code (iCode) generated 
by the compiler in human readable form at various 
stages of the compilation process. More on iCodes see 
chapter [sub:The-anatomy-of] "The anatomy of the compiler".

--dumpraw This option will cause the compiler to dump 
the intermediate code into a file of named <source 
filename>.dumpraw just after the intermediate code has 
been generated for a function, i.e. before any 
optimizations are done. The basic blocks at this stage 
ordered in the depth first number, so they may not be 
in sequence of execution.

--dumpgcse Will create a dump of iCodes, after global 
subexpression elimination, into a file named <source 
filename>.dumpgcse.

--dumpdeadcode Will create a dump of iCodes, after 
deadcode elimination, into a file named <source 
filename>.dumpdeadcode.

--dumploop Will create a dump of iCodes, after loop optimizations
, into a file named <source filename>.dumploop.

--dumprange Will create a dump of iCodes, after live 
range analysis, into a file named <source filename>.dumprange.

--dumlrange Will dump the life ranges for all symbols.

--dumpregassign Will create a dump of iCodes, after 
register assignment, into a file named <source 
filename>.dumprassgn.

--dumplrange Will create a dump of the live ranges of iTemp's

--dumpall Will cause all the above mentioned dumps to 
be created.





3.2.11 Redirecting output on Windows Shells

By default SDCC writes its error messages to "standard error"
. To force all messages to "standard output" use --use-stdout
. Additionally, if you happen to have visual studio 
installed in your windows machine, you can use it to 
compile your sources using a custom build and the SDCC --vc
 option. Something like this should work:


c:\sdcc\bin\sdcc.exe --vc --model-large -c $(InputPath)



3.3 Environment variables

SDCC recognizes the following environment variables:

SDCC_LEAVE_SIGNALS SDCC installs a signal handler to be 
able to delete temporary files after an user break (^C) 
or an exception. If this environment variable is set, 
SDCC won't install the signal handler in order to be 
able to debug SDCC.

TMP, TEMP, TMPDIR Path, where temporary files will be 
created. The order of the variables is the search 
order. In a standard *nix environment these variables 
are not set, and there's no need to set them. On 
Windows it's recommended to set one of them.

SDCC_HOME Path, see section [sub:Install-paths] " Install Paths".

SDCC_INCLUDE Path, see section [sub:Search-Paths] "Search Paths".

SDCC_LIB Path, see section [sub:Search-Paths] "Search Paths"..

There are some more environment variables recognized by 
SDCC, but these are solely used for debugging purposes. 
They can change or disappear very quickly, and will 
never be documented.



3.4 Storage Class Language Extensions

3.4.1 MCS51/DS390 Storage Class Language Extensions

In addition to the ANSI storage classes SDCC allows the 
following MCS51 specific storage classes:

3.4.1.1 data / near

This is the default storage class for the Small Memory 
model (data and near or the more ANSI-C compliant forms 
__data and __near can be used synonymously). Variables 
declared with this storage class will be allocated in 
the directly addressable portion of the internal RAM of 
a 8051, e.g.:

__data unsigned char test_data;

Writing 0x01 to this variable generates the assembly code:

75*00 01   mov  _test_data,#0x01

3.4.1.2 xdata / far

Variables declared with this storage class will be 
placed in the external RAM. This is the default storage 
class for the Large Memory model, e.g.:

__xdata unsigned char test_xdata;

Writing 0x01 to this variable generates the assembly code:

90s00r00   mov  dptr,#_test_xdata 
74 01      mov  a,#0x01 
F0         movx 
@dptr,a 

3.4.1.3 idata

Variables declared with this storage class will be 
allocated into the indirectly addressable portion of 
the internal ram of a 8051, e.g.:

__idata unsigned char test_idata;

Writing 0x01 to this variable generates the assembly code:

78r00       mov  r0,#_test_idata
76 01       mov  @r0,#0x01

Please note, the first 128 byte of idata physically 
access the same RAM as the data memory. The original 
8051 had 128 byte idata memory, nowadays most devices 
have 256 byte idata memory. The stack is located in 
idata memory.

3.4.1.4 pdata

Paged xdata access is just as straightforward as using 
the other addressing modes of a 8051. It is typically 
located at the start of xdata and has a maximum size of 
256 bytes. The following example writes 0x01 to the 
pdata variable. Please note, pdata access physically 
accesses xdata memory. The high byte of the address is 
determined by port P2 (or in case of some 8051 variants 
by a separate Special Function Register, see section [sub:MCS51-variants]). 
This is the default storage class for the Medium Memory 
model, e.g.:

__pdata unsigned char test_pdata;

Writing 0x01 to this variable generates the assembly code:

78r00      mov r0,#_test_pdata
74 01      mov a,#0x01 
F2         movx @r0,a

If the --xstack option is used the pdata memory area is 
followed by the xstack memory area and the sum of their 
sizes is limited to 256 bytes.

3.4.1.5 code

'Variables' declared with this storage class will be 
placed in the code memory:

__code unsigned char test_code;

Read access to this variable generates the assembly code:

90s00r6F   mov dptr,#_test_code
E4         clr a
93         movc a,@a+dptr 

char indexed arrays of characters in code memory can be 
accessed efficiently:

__code char test_array[] = {'c','h','e','a','p'}; 

Read access to this array using an 8-bit unsigned index 
generates the assembly code:

E5*00      mov a,_index 

90s00r41   mov dptr,#_test_array

93         movc a,@a+dptr 

3.4.1.6 bit

This is a data-type and a storage class specifier. When 
a variable is declared as a bit, it is allocated into 
the bit addressable memory of 8051, e.g.:

__bit test_bit;

Writing 1 to this variable generates the assembly code:

D2*00       setb _test_bit

The bit addressable memory consists of 128 bits which 
are located from 0x20 to 0x2f in data memory. 
Apart 
from this 8051 specific storage class most 
architectures support ANSI-C bitfields

Not really meant as examples, but nevertheless showing 
what bitfields are about: device/include/mc68hc908qy.h 
and support/regression/tests/bitfields.c
. In accordance with ISO/IEC 9899 bits and bitfields 
without an explicit signed modifier are implemented as unsigned.

3.4.1.7 sfr / sfr16 / sfr32 / sbit

Like the bit keyword, sfr / sfr16 / sfr32 / sbit 
signify both a data-type and storage class, they are 
used to describe the special function registers and 
special bit variables of a 8051, eg:

__sfr __at (0x80) P0;  /* special function register P0 
at location 0x80 */

/* 16 bit special function register 
combination for timer 0
   with the high byte at location 
0x8C and the low byte at location 0x8A */
__sfr16 __at 
(0x8C8A) TMR0;

__sbit __at (0xd7) CY;  /* CY (Carry Flag) */

Special function registers which are located on an 
address dividable by 8 are bit-addressable, an sbit 
addresses a specific bit within these sfr.
16 Bit and 32 
bit special function register combinations which 
require a certain access order are better not declared 
using sfr16 or sfr32. Allthough SDCC usually accesses 
them Least Significant Byte (LSB) first, this is not guaranteed.


Please note, if you use a header file which was written 
for another compiler then the sfr / sfr16 / sfr32 / 
sbit Storage Class extensions will most likely be not 
compatible. Specifically the syntax  sfr P0 = 0x80;  is 
compiled without warning by SDCC to an assignment of 
0x80 to a variable called P0 

 !
. Nevertheless it is possible to write header files 
which can be shared among different compilers (see 
section [sec:Porting-code-to-other-compilers]). 

3.4.1.8 Pointers to MCS51/DS390 specific memory spaces

SDCC allows (via language extensions) pointers to 
explicitly point to any of the memory spaces of the 
8051. In addition to the explicit pointers, the 
compiler uses (by default) generic pointers which can 
be used to point to any of the memory spaces.

Pointer 
declaration examples:

/* pointer physically in internal ram pointing to 
object in external ram */ 
__xdata unsigned char * 
__data p;

/* pointer physically in external ram pointing 
to object in internal ram */ 
__data unsigned char * 
__xdata p;

/* pointer physically in code rom pointing to 
data in xdata space */ 
__xdata unsigned char * __code p;


/* pointer physically in code space pointing to data in 
code space */ 
__code unsigned char * __code p;

/* 
generic pointer physically located in xdata space */

unsigned char * __xdata p;

/* generic pointer physically 
located in default memory space */
unsigned char * p;

/* 
the following is a function pointer physically located 
in data space */
char (* __data fp)(void);

Well you get the idea. 

All unqualified pointers are 
treated as 3-byte (4-byte for the ds390) generic 
pointers. 

The highest order byte of the generic 
pointers contains the data space information. Assembler 
support routines are called whenever data is stored or 
retrieved using generic pointers. These are useful for 
developing reusable library routines. Explicitly 
specifying the pointer type will generate the most 
efficient code.

3.4.1.9 Notes on MCS51 memory layout

The 8051 family of microcontrollers have a minimum of 
128 bytes of internal RAM memory which is structured as follows:


- Bytes 00-1F - 32 bytes to hold up to 4 banks of the 
registers R0 to R7, 
- Bytes 20-2F - 16 bytes to hold 
128 bit variables and, 
- Bytes 30-7F - 80 bytes for 
general purpose use.


Additionally some members of the MCS51 family may have 
up to 128 bytes of additional, indirectly addressable, 
internal RAM memory (idata). Furthermore, some chips 
may have some built in external memory (xdata) which 
should not be confused with the internal, directly 
addressable RAM memory (data). Sometimes this built in 
xdata memory has to be activated before using it (you 
can probably find this information on the datasheet of 
the microcontroller your are using, see also section [sub:Startup-Code] 
Startup-Code).

Normally SDCC will only use the first bank of registers 
(register bank 0), but it is possible to specify that 
other banks of registers (keyword using ) should be 
used for example in interrupt routines. By default, the 
compiler will place the stack after the last byte of 
allocated memory for variables. For example, if the 
first 2 banks of registers are used, and only four 
bytes are used for data variables, it will position the 
base of the internal stack at address 20 (0x14). This 
implies that as the stack grows, it will use up the 
remaining register banks, and the 16 bytes used by the 
128 bit variables, and 80 bytes for general purpose 
use. If any bit variables are used, the data variables 
will be placed in unused register banks and after the 
byte holding the last bit variable. For example, if 
register banks 0 and 1 are used, and there are 9 bit 
variables (two bytes used), data variables will be 
placed starting from address 0x10 to 0x20 and continue 
at address 0x22. You can also use --data-loc to specify 
the start address of the data and --iram-size to 
specify the size of the total internal RAM 
(data+idata). 


By default the 8051 linker will place the stack after 
the last byte of (i)data variables. Option --stack-loc 
allows you to specify the start of the stack, i.e. you 
could start it after any data in the general purpose 
area. If your microcontroller has additional indirectly 
addressable internal RAM (idata) you can place the 
stack on it. You may also need to use --xdata-loc to 
set the start address of the external RAM (xdata) and --xram-size
 to specify its size. Same goes for the code memory, 
using --code-loc and --code-size. If in doubt, don't 
specify any options and see if the resulting memory 
layout is appropriate, then you can adjust it.

The linker generates two files with memory allocation 
information. The first, with extension .map shows all 
the variables and segments. The second with extension .mem
 shows the final memory layout. The linker will 
complain either if memory segments overlap, there is 
not enough memory, or there is not enough space for 
stack. If you get any linking warnings and/or errors 
related to stack or segments allocation, take a look at 
either the .map or .mem files to find out what the 
problem is. The .mem file may even suggest a solution 
to the problem.



3.4.2 Z80/Z180 Storage Class Language Extensions

3.4.2.1 sfr (in/out to 8-bit addresses)

The Z80 family has separate address spaces for memory 
and input/output memory. I/O memory is accessed with 
special instructions, e.g.:

sfr at 0x78 IoPort;  /* define a var in I/O space at 78h 
called IoPort */ 

Writing 0x01 to this variable generates the assembly code:

3E 01      ld a,#0x01
D3 78      out (_IoPort),a 

3.4.2.2 banked sfr (in/out to 16-bit addresses)

The keyword banked is used to support 16 bit addresses 
in I/O memory e.g.:

sfr banked at 0x123 IoPort; 

Writing 0x01 to this variable generates the assembly code:

01 23 01   ld bc,#_IoPort
3E 01      ld a,#0x01 
ED 79      out (c),a 

3.4.2.3 sfr (in0/out0 to 8 bit addresses on Z180/HD64180)

The compiler option --portmode=180 (80) and a compiler #pragma 
portmode z180 (z80) is used to turn on (off) the 
Z180/HD64180 port addressing instructions in0/out0 
instead of in/out. If you include the file z180.h this 
will be set automatically.



3.4.3 HC08 Storage Class Language Extensions

3.4.3.1 data 

The data storage class declares a variable that resides 
in the first 256 bytes of memory (the direct page). The HC08
 is most efficient at accessing variables (especially 
pointers) stored here.

3.4.3.2 xdata 

The xdata storage class declares a variable that can 
reside anywhere in memory. This is the default if no 
storage class is specified. 



3.5 Absolute Addressing

Data items can be assigned an absolute address with the at
 <address> keyword, in addition to a storage class, e.g.:

xdata at 0x7ffe unsigned int chksum;

or, better conforming to ISO/IEC 9899 C:

__xdata __at (0x7ffe) unsigned int chksum;

In the above example the variable chksum will be 
located at 0x7ffe and 0x7fff of the external ram. The 
compiler does not reserve any space for variables 
declared in this way

 !
 (they are implemented with an equate in the 
assembler). Thus it is left to the programmer to make 
sure there are no overlaps with other variables that 
are declared without the absolute address. The 
assembler listing file (.lst) and the linker output 
files (.rst) and (.map) are good places to look for 
such overlaps.

If however you provide an initializer actual memory 
allocation will take place and overlaps will be 
detected by the linker. E.g.:

__code __at (0x7ff0) char Id[5] = "SDCC";

In the above example the variable Id will be located 
from 0x7ff0 to 0x7ff4 in code memory.

In case of memory mapped I/O devices the keyword 
volatile has to be used to tell the compiler that 
accesses might not be removed:

volatile __xdata __at (0x8000) unsigned char PORTA_8255;

For some architectures (mcs51) array accesses are more 
efficient if an (xdata/far) array starts at a block 
(256 byte) boundary (section [sub:A-Step-by Assembler Introduction] has an example).
Absolute 
addresses can be specified for variables in all storage 
classes, e.g.:

__bit __at (0x02) bvar;

The above example will allocate the variable at offset 
0x02 in the bit-addressable space. There is no real 
advantage to assigning absolute addresses to variables 
in this manner, unless you want strict control over all 
the variables allocated. One possible use would be to 
write hardware portable code. For example, if you have 
a routine that uses one or more of the microcontroller 
I/O pins, and such pins are different for two different 
hardwares, you can declare the I/O pins in your routine using:

extern volatile __bit MOSI;    /* master out, slave in */

extern volatile __bit MISO;    /* master in, slave out */

extern volatile __bit MCLK;    /* master clock */

/* Input 
and Output of a byte on a 3-wire serial bus.
   If needed 
adapt polarity of clock, polarity of data and bit order
 */

unsigned char spi_io(unsigned char out_byte) 
{ 
    unsigned 
char i=8;
    do { 
        MOSI = out_byte & 0x80; 
        out_byte <<= 1;
        
MCLK = 1; 
        /* _asm nop _endasm; */        /* for slow 
peripherals */
        if(MISO) 
            out_byte += 1; 
        MCLK = 0; 
    } while(--i);
    
return out_byte; 
}

Then, someplace in the code for the first hardware you 
would use

__bit __at (0x80) MOSI;    /* I/O port 0, bit 0 */
__bit 
__at (0x81) MISO;    /* I/O port 0, bit 1 */
__bit __at 
(0x82) MCLK;    /* I/O port 0, bit 2 */

Similarly, for the second hardware you would use

__bit __at (0x83) MOSI;    /* I/O port 0, bit 3 */
__bit 
__at (0x91) MISO;    /* I/O port 1, bit 1 */
__bit __at 
(0x92) MCLK;    /* I/O port 1, bit 2 */

and you can use the same hardware dependent routine 
without changes, as for example in a library. This is 
somehow similar to sbit, but only one absolute address 
has to be specified in the whole project.



3.6 Parameters & Local Variables<sec:Parameters-and-Local-Variables>

Automatic (local) variables and parameters to functions 
can either be placed on the stack or in data-space. The 
default action of the compiler is to place these 
variables in the internal RAM (for small model) or 
external RAM (for medium or large model). This in fact 
makes them similar to static so by default functions 
are non-reentrant. 

They can be placed on the stack by 
using the --stack-auto option, by using #pragma stackauto
 or by using the reentrant keyword in the function 
declaration, e.g.:

unsigned char foo(char i) __reentrant 
{ 
    ... 
}

Since stack space on 8051 is limited, the reentrant 
keyword or the --stack-auto option should be used 
sparingly. Note that the reentrant keyword just means 
that the parameters & local variables will be allocated 
to the stack, it does not mean that the function is 
register bank independent.

Local variables can be 
assigned storage classes and absolute addresses, e.g.: 

unsigned char foo() 
{
    __xdata unsigned char i;
    __bit bvar;
    
__data __at (0x31) unsigned char j;
    ... 
}

In the above example the variable i will be allocated 
in the external ram, bvar in bit addressable space and 
j in internal ram. When compiled with --stack-auto or 
when a function is declared as reentrant this should 
only be done for static variables.

Parameters however are not allowed any storage class, 
(storage classes for parameters will be ignored), their 
allocation is governed by the memory model in use, and 
the reentrancy options.

It is however allowed to use bit parameters in 
reentrant functions and also non-static local bit 
variables are supported. Efficient use is limited to 8 
semi-bitregisters in bit space. They are pushed and 
popped to stack as a single byte just like the normal registers.

3.7 Overlaying<sub:Overlaying>

For non-reentrant functions SDCC will try to reduce 
internal ram space usage by overlaying parameters and 
local variables of a function (if possible). Parameters 
and local variables of a function will be allocated to 
an overlayable segment if the function has no other 
function calls and the function is non-reentrant and 
the memory model is small. If an explicit storage class 
is specified for a local variable, it will NOT be overlayed.

Note that the compiler (not the linkage editor) makes 
the decision for overlaying the data items. Functions 
that are called from an interrupt service routine

!
 should be preceded by a #pragma nooverlay if they are 
not reentrant.

Also note that the compiler does not do any processing 
of inline assembler code, so the compiler might 
incorrectly assign local variables and parameters of a 
function into the overlay segment if the inline 
assembler code calls other c-functions that might use 
the overlay. In that case the #pragma nooverlay should 
be used.

Parameters and local variables of functions that 
contain 16 or 32 bit multiplication or division will 
NOT be overlayed since these are implemented using 
external functions, e.g.:

#pragma save 
#pragma nooverlay 
void set_error(unsigned 
char errcd) 
{
    P3 = errcd;
} 
#pragma restore 

void some_isr 
() __interrupt (2)
{
    ...
    set_error(10);
    ... 
}

In the above example the parameter errcd for the 
function set_error would be assigned to the overlayable 
segment if the #pragma nooverlay was not present, this 
could cause unpredictable runtime behavior when called 
from an interrupt service routine. The #pragma nooverlay 
ensures that the parameters and local variables for the 
function are NOT overlayed.



3.8 Interrupt Service Routines<sub:Interrupt-Service-Routines>

3.8.1 General Information

SDCC allows interrupt service routines to be coded in 
C, with some extended keywords.

void timer_isr (void) __interrupt (1) __using (1) 
{ 
    ... 
}

The optional number following the interrupt keyword is 
the interrupt number this routine will service. When 
present, the compiler will insert a call to this 
routine in the interrupt vector table for the interrupt 
number specified. If you have multiple source files in 
your project, interrupt service routines can be present 
in any of them, but a prototype of the isr MUST be 
present or included in the file that contains the 
function main. The optional (8051 specific) keyword using
 can be used to tell the compiler to use the specified 
register bank when generating code for this function. 

Interrupt service routines open the door for some very 
interesting bugs:

3.8.1.1 <sub:Common-interrupt-pitfall-volatile>Common interrupt pitfall: variable not declared volatile

If an interrupt service routine changes variables which 
are accessed by other functions these variables have to 
be declared volatile. See [http://en.wikipedia.org/wiki/Volatile_variable] .

3.8.1.2 <sub:Common-interrupt-pitfall-non-atomic>Common interrupt pitfall: non-atomic access

If the access to these variables is not atomic (i.e. 
the processor needs more than one instruction for the 
access and could be interrupted while accessing the 
variable) the interrupt must be disabled during the 
access to avoid inconsistent data. 
Access to 16 or 32 
bit variables is obviously not atomic on 8 bit CPUs and 
should be protected by disabling interrupts. You're not 
automatically on the safe side if you use 8 bit 
variables though. We need an example here: f.e. on the 
8051 the harmless looking "flags |= 0x80;" is not atomic if 
flags resides in xdata. Setting "flags |= 0x40;" from 
within an interrupt routine might get lost if the 
interrupt occurs at the wrong time. "counter += 8;" is not 
atomic on the 8051 even if counter is located in data memory.

Bugs like these are hard to reproduce and can cause a 
lot of trouble. 

3.8.1.3 <sub:Common-interrupt-pitfall-stack-overflow>Common interrupt pitfall: stack overflow

The return address and the registers used in the 
interrupt service routine are saved on the stack so 
there must be sufficient stack space. If there isn't 
variables or registers (or even the return address 
itself) will be corrupted. This stack overflow is most 
likely to happen if the interrupt occurs during the "deepest"
 subroutine when the stack is already in use for f.e. 
many return addresses.

3.8.1.4 <sub:Common-interrupt-pitfall-non-reentrant>Common interrupt pitfall: use of non-reentrant functions

A special note here, int (16 bit) and long (32 bit) 
integer division, multiplication & modulus and floating-point
 operations are implemented using external support 
routines. If an interrupt service routine needs to do 
any of these operations then the support routines (as 
mentioned in a following section) will have to be 
recompiled using the --stack-auto option and the source 
file will need to be compiled using the --int-long-reent
 compiler option. 
Note, the type promotion required by 
ANSI C can cause 16 bit routines to be used

 !
 without the programmer being aware of it. See f.e. the 
cast (unsigned char)(tail-1) within the if clause in 
section [sub:A-Step-by Assembler Introduction].

Calling other functions from an interrupt service 
routine is not recommended, avoid it if possible. Note 
that when some function is called from an interrupt 
service routine it should be preceded by a #pragma nooverlay
 if it is not reentrant. Furthermore nonreentrant 
functions should not be called from the main program 
while the interrupt service routine might be active. 
They also must not be called from low priority 
interrupt service routines while a high priority 
interrupt service routine might be active. You could 
use semaphores or make the function critical if all 
parameters are passed in registers.
 Also see section [sub:Overlaying] 
about Overlaying and section [sub:Functions-using-private-banks] about Functions using 
private register banks.



3.8.2 MCS51/DS390 Interrupt Service Routines

Interrupt numbers and the corresponding address & 
descriptions for the Standard 8051/8052 are listed 
below. SDCC will automatically adjust the  to the 
maximum interrupt number specified.


+----------------+-------------------+------------------+
| 

Interrupt #  | 

Description     | 

Vector Address |
+----------------+-------------------+------------------+
+----------------+-------------------+------------------+
|      

0       | 

External 0      | 

0x0003         |
+----------------+-------------------+------------------+
|      

1       | 

Timer 0         | 

0x000b         |
+----------------+-------------------+------------------+
|      

2       | 

External 1      | 

0x0013         |
+----------------+-------------------+------------------+
|      

3       | 

Timer 1         | 

0x001b         |
+----------------+-------------------+------------------+
|      

4       | 

Serial          | 

0x0023         |
+----------------+-------------------+------------------+
|      

5       | 

Timer 2 (8052)  | 

0x002b         |
+----------------+-------------------+------------------+
|     

...      | 

                | 

...            |
+----------------+-------------------+------------------+
|      

n       | 

                | 

0x0003 + 8*n   |
+----------------+-------------------+------------------+



If the interrupt service routine is defined without using
 a register bank or with register bank 0 (using 0), the 
compiler will save the registers used by itself on the 
stack upon entry and restore them at exit, however if 
such an interrupt service routine calls another 
function then the entire register bank will be saved on 
the stack. This scheme may be advantageous for small 
interrupt service routines which have low register usage.

If the interrupt service routine is defined to be using 
a specific register bank then only a, b, dptr & psw are 
saved and restored, if such an interrupt service 
routine calls another function (using another register 
bank) then the entire register bank of the called 
function will be saved on the stack. This scheme is 
recommended for larger interrupt service routines.



3.8.3 HC08 Interrupt Service Routines

Since the number of interrupts available is chip 
specific and the interrupt vector table always ends at 
the last byte of memory, the interrupt numbers 
corresponds to the interrupt vectors in reverse order 
of address. For example, interrupt 1 will use the 
interrupt vector at 0xfffc, interrupt 2 will use the 
interrupt vector at 0xfffa, and so on. However, 
interrupt 0 (the reset vector at 0xfffe) is not 
redefinable in this way; instead see section [sub:Startup-Code] for 
details on customizing startup.



3.8.4 Z80 Interrupt Service Routines

The Z80 uses several different methods for determining 
the correct interrupt vector depending on the hardware 
implementation. Therefore, SDCC ignores the optional 
interrupt number and does not attempt to generate an 
interrupt vector table.

By default, SDCC generates code for a maskable 
interrupt, which uses a RETI instruction to return from 
the interrupt. To write an interrupt handler for the 
non-maskable interrupt, which needs a RETN instruction 
instead, add the critical keyword:

void nmi_isr (void) critical interrupt
{ 
    ... 
}

However if you need to create a non-interruptable 
interrupt service routine you would also require the 
critical keyword. To distinguish between this and an 
nmi_isr you must provide an interrupt number.



3.9 Enabling and Disabling Interrupts

3.9.1 Critical Functions and Critical Statements

A special keyword may be associated with a block or a 
function declaring it as critical. SDCC will generate 
code to disable all interrupts upon entry to a critical 
function and restore the interrupt enable to the 
previous state before returning. Nesting critical 
functions will need one additional byte on the stack 
for each call.

int foo () __critical 
{ 
    ... 
    ... 
}

The critical attribute maybe used with other attributes 
like reentrant.
The keyword critical may also be used to 
disable interrupts more locally:

__critical{ i++; }

More than one statement could have been included in the block.

3.9.2 Enabling and Disabling Interrupts directly

Interrupts can also be disabled and enabled directly (8051):

EA = 0;            or:           EA_SAVE = EA;

...                              EA = 0;

EA = 1;                          ...

                                 EA = EA_SAVE;

On other architectures which have seperate opcodes for 
enabling and disabling interrupts you might want to 
make use of defines with inline assembly (HC08):

#define CLI _asm  cli  _endasm; 

#define SEI _asm  sei  _endasm; 

...

Note: it is sometimes sufficient to disable only a 
specific interrupt source like f.e. a timer or serial 
interrupt by manipulating an interrupt mask register. 

Usually the time during which interrupts are disabled 
should be kept as short as possible. This minimizes 
both interrupt latency (the time between the occurrence 
of the interrupt and the execution of the first code in 
the interrupt routine) and interrupt jitter (the 
difference between the shortest and the longest 
interrupt latency). These really are something 
different, f.e. a serial interrupt has to be served 
before its buffer overruns so it cares for the maximum 
interrupt latency, whereas it does not care about 
jitter. On a loudspeaker driven via a digital to analog 
converter which is fed by an interrupt a latency of a 
few milliseconds might be tolerable, whereas a much 
smaller jitter will be very audible.

You can reenable interrupts within an interrupt routine 
and on some architectures you can make use of two (or 
more) levels of interrupt priorities. On some 
architectures which don't support interrupt priorities 
these can be implemented by manipulating the interrupt 
mask and reenabling interrupts within the interrupt 
routine. Check there is sufficient space on the stack 
and don't add complexity unless you have to. 

3.9.3 Semaphore locking (mcs51/ds390)

Some architectures (mcs51/ds390) have an atomic bit 
test and clear instruction. These type of instructions 
are typically used in preemptive multitasking systems, 
where a routine f.e. claims the use of a data structure 
('acquires a lock on it'), makes some modifications and 
then releases the lock when the data structure is 
consistent again. The instruction may also be used if 
interrupt and non-interrupt code have to compete for a 
resource. With the atomic bit test and clear 
instruction interrupts don't have to be disabled for 
the locking operation. 

SDCC generates this instruction if the source follows 
this pattern:

volatile bit resource_is_free; 

if (resource_is_free) 
  { 
    
resource_is_free=0; 
    ... 
    resource_is_free=1;
  } 

Note, mcs51 and ds390 support only an atomic bit test 
and clear instruction (as opposed to atomic bit test 
and set).

3.10 Functions using private register banks<sub:Functions-using-private-banks> (mcs51/ds390)

Some architectures have support for quickly changing 
register sets. SDCC supports this feature with the using
 attribute (which tells the compiler to use a register bank
 other than the default bank zero). It should only be 
applied to interrupt functions (see footnote below). 
This will in most circumstances make the generated ISR 
code more efficient since it will not have to save 
registers on the stack.

The using attribute will have no effect on the 
generated code for a non-interrupt function (but may 
occasionally be useful anyway

possible exception: if a function is called ONLY from 
'interrupt' functions using a particular bank, it can 
be declared with the same 'using' attribute as the 
calling 'interrupt' functions. For instance, if you 
have several ISRs using bank one, and all of them call 
memcpy(), it might make sense to create a specialized 
version of memcpy() 'using 1', since this would prevent 
the ISR from having to save bank zero to the stack on 
entry and switch to bank zero before calling the function
).
(pending: Note, nowadays the using attribute has an 
effect on the generated code for a non-interrupt function.)

An interrupt function using a non-zero bank will assume 
that it can trash that register bank, and will not save 
it. Since high-priority interrupts can interrupt 
low-priority ones on the 8051 and friends, this means 
that if a high-priority ISR using a particular bank 
occurs while processing a low-priority ISR using the 
same bank, terrible and bad things can happen. To 
prevent this, no single register bank should be used by 
both a high priority and a low priority ISR. This is 
probably most easily done by having all high priority 
ISRs use one bank and all low priority ISRs use 
another. If you have an ISR which can change priority 
at runtime, you're on your own: I suggest using the 
default bank zero and taking the small performance hit.

It is most efficient if your ISR calls no other 
functions. If your ISR must call other functions, it is 
most efficient if those functions use the same bank as 
the ISR (see note 1 below); the next best is if the 
called functions use bank zero. It is very inefficient 
to call a function using a different, non-zero bank 
from an ISR. 



3.11 Startup Code<sub:Startup-Code>

3.11.1 MCS51/DS390 Startup Code

The compiler triggers the linker to link certain 
initialization modules from the runtime library called 
crt<something>. Only the necessary ones are linked, for 
instance crtxstack.asm (GSINIT1, GSINIT5) is not linked 
unless the --xstack option is used. These modules are 
highly entangled by the use of special segments/areas, 
but a common layout is shown below:

(main.asm)

        .area HOME (CODE)
__interrupt_vect:
        ljmp __sdcc_gsinit_startup

(crtstart.asm)

        .area GSINIT0 (CODE)
__sdcc_gsinit_startup::
        mov 
sp,#__start__stack - 1

(crtxstack.asm)

        .area GSINIT1 (CODE)
__sdcc_init_xstack::
; Need to 
initialize in GSINIT1 in case the user's 
__sdcc_external_startup uses the xstack.
        mov 
__XPAGE,#(__start__xstack >> 8)
        mov _spx,#__start__xstack

(crtstart.asm)

        .area GSINIT2 (CODE)
        lcall __sdcc_external_startup
        mov a,dpl
        
jz __sdcc_init_data
        ljmp __sdcc_program_startup
__sdcc_init_data:

(crtxinit.asm)

        .area GSINIT3 (CODE)
__mcs51_genXINIT::
        mov r1,#l_XINIT
        
mov a,r1
        orl a,#(l_XINIT >> 8)
        jz 00003$
        mov 
r2,#((l_XINIT+255) >> 8)
        mov dptr,#s_XINIT
        mov r0,#s_XISEG
        
mov __XPAGE,#(s_XISEG >> 8)
00001$: clr a
        movc a,@a+dptr
        
movx @r0,a
        inc dptr
        inc r0
        cjne r0,#0,00002$
        inc __XPAGE
00002$: 
djnz r1,00001$
        djnz r2,00001$
        mov __XPAGE,#0xFF
00003$:

(crtclear.asm)

        .area GSINIT4 (CODE)
__mcs51_genRAMCLEAR::
        clr a
        mov r0,#(l_IRAM-1)

00004$: mov @r0,a
        djnz r0,00004$
; _mcs51_genRAMCLEAR() end

(crtxclear.asm)

        .area GSINIT4 (CODE)
__mcs51_genXRAMCLEAR::
        mov r0,#l_PSEG
        
mov a,r0
        orl a,#(l_PSEG >> 8)
        jz 00006$
        mov r1,#s_PSEG
        mov 
__XPAGE,#(s_PSEG >> 8)
        clr a
00005$: movx @r1,a
        inc r1
        djnz r0,00005$

00006$:
        mov r0,#l_XSEG
        mov a,r0
        orl a,#(l_XSEG >> 8)
        jz 00008$
        
mov r1,#((l_XSEG + 255) >> 8)
        mov dptr,#s_XSEG
        clr a
00007$: 
movx @dptr,a
        inc dptr
        djnz r0,00007$
        djnz r1,00007$
00008$:

(crtxstack.asm)

        .area GSINIT5 (CODE)
; Need to initialize in GSINIT5 
because __mcs51_genXINIT modifies __XPAGE
; and 
__mcs51_genRAMCLEAR modifies _spx.
        mov 
__XPAGE,#(__start__xstack >> 8)
        mov _spx,#__start__xstack

(application modules)

        .area GSINIT (CODE)

(main.asm)

        .area GSFINAL (CODE)
        ljmp __sdcc_program_startup

;--------------------------------------------------------

; Home
;--------------------------------------------------------
        
.area HOME (CODE)
        .area CSEG (CODE)
__sdcc_program_startup:
        
lcall _main
; return from main will lock up
        sjmp .

One of these modules (crtstart.asm) contains a call to 
the C routine _sdcc_external_startup() at the start of 
the CODE area. This routine is also in the runtime library
 and returns 0 by default. If this routine returns a 
non-zero value, the static & global variable 
initialization will be skipped and the function main 
will be invoked. Otherwise static & global variables 
will be initialized before the function main is 
invoked. You could add an _sdcc_external_startup() 
routine to your program to override the default if you 
need to setup hardware or perform some other critical 
operation prior to static & global variable initialization
. On some mcs51 variants xdata memory has to be 
explicitly enabled before it can be accessed or if the watchdog
 needs to be disabled, this is the place to do it. The 
startup code clears all internal data memory, 256 bytes 
by default, but from 0 to n-1 if --iram-sizen is used. 
(recommended for Chipcon CC1010).

See also the compiler options --no-xinit-opt, --main-return
 and section [sub:MCS51-variants] about MCS51-variants.


While these initialization modules are meant as generic 
startup code there might be the need for customization. 
Let's assume the return value of 
_sdcc_external_startup() in crtstart.asm should not be 
checked (or _sdcc_external_startup() should not be 
called at all). The recommended way would be to copy 
crtstart.asm (f.e. from [http://sdcc.svn.sourceforge.net/viewvc/*checkout*/sdcc/trunk/sdcc/device/lib/mcs51/crtstart.asm]) into the source directory, 
adapt it there, then assemble it with asx8051 -plosgff

"-plosgff" are the assembler options used in [http://sdcc.svn.sourceforge.net/viewvc/sdcc/trunk/sdcc/device/lib/mcs51/Makefile.in?view=markup ]
 crtstart.asm and when linking your project explicitely 
specify crtstart.rel. As a bonus a listing of the 
relocated object file crtstart.rst is generated.





3.11.2 HC08 Startup Code

The HC08 startup code follows the same scheme as the 
MCS51 startup code.



3.11.3 Z80 Startup Code

On the Z80 the startup code is inserted by linking with 
crt0.o which is generated from 
sdcc/device/lib/z80/crt0.s. If you need a different 
startup code you can use the compiler option --no-std-crt0
 and provide your own crt0.o. 



3.12 Inline Assembler Code

3.12.1 A Step by Step Introduction<sub:A-Step-by Assembler Introduction>

Starting from a small snippet of c-code this example 
shows for the MCS51 how to use inline assembly, access 
variables, a function parameter and an array in xdata 
memory. The example uses an MCS51 here but is easily 
adapted for other architectures. This is a buffer 
routine which should be optimized:

unsigned char __far __at(0x7f00) buf[0x100];
unsigned 
char head, tail;                 /* if interrupts are involved see
                                             
section [sub:Common-interrupt-pitfall-volatile] about volatile */

void to_buffer( unsigned char 
c ) 
{
    if( head != (unsigned char)(tail-1) ) /* cast 
needed to avoid promotion to integer */

 !
        
buf[ head++ ] = c;                /* access to a 256 byte aligned array */

} 

If the code snippet (assume it is saved in buffer.c) is 
compiled with SDCC then a corresponding buffer.asm file 
is generated. We define a new function to_buffer_asm() 
in file buffer.c in which we cut and paste the 
generated code, removing unwanted comments and some 
':'. Then add "_asm" and "_endasm;"

Note, that the single underscore form (_asm and 
_endasm) are not C99-compatible, and for C-99 
compatibility, the double-underscore form (__asm and 
__endasm) has to be used. The latter is also used in 
the library functions.
 to the beginning and the end of the function body:

/* With a cut and paste from the .asm file, we have 
something to start with.
   The function is not yet OK! 
(registers aren't saved) */ 
void to_buffer_asm( 
unsigned char c ) 
{ 
    _asm
    mov  r2,dpl 
;buffer.c if( head != 
(unsigned char)(tail-1) )  /* cast needed to avoid promotion
 to integer */
    mov  a,_tail 
    dec  a 
    mov  r3,a 
    mov  a,_head 
    cjne 
a,ar3,00106$ 
    ret
00106$: 
;buffer.c buf[ head++ ] = c; /* 
access to a 256 byte aligned array */
    mov  r3,_head 
    inc  
_head 
    mov  dpl,r3 
    mov  dph,#(_buf >> 8) 
    mov  a,r2 
    movx 
@dptr,a 
00103$: 
    ret
    _endasm;
} 

The new file buffer.c should compile with only one 
warning about the unreferenced function argument 'c'. 
Now we hand-optimize the assembly code and insert an 
#define USE_ASSEMBLY (1) and finally have:

unsigned char __far __at(0x7f00) buf[0x100];
unsigned 
char head, tail;
#define USE_ASSEMBLY (1)

#if !USE_ASSEMBLY


void to_buffer( unsigned char c )
{
    if( head != (unsigned 
char)(tail-1) )
        buf[ head++ ] = c;
}

#else

void to_buffer( 
unsigned char c )
{
    c; // to avoid warning: unreferenced 
function argument
    _asm
        ; save used registers here. 
        ; If 
we were still using r2,r3 we would have to push them 
here. 
; if( head != (unsigned char)(tail-1) )
        mov  a,_tail
        dec 
 a
        xrl  a,_head
        ; we could do an ANL a,#0x0f here to use a 
smaller buffer (see below)
        jz   t_b_end$
        ;
; buf[ head++ ] = c;
        mov 
 a,dpl        ; dpl holds lower byte of function argument
        mov  
dpl,_head    ; buf is 0x100 byte aligned so head can be 
used directly
        mov  dph,#(_buf>>8)
        movx @dptr,a
        inc  _head
        ; 
we could do an ANL _head,#0x0f here to use a smaller 
buffer (see above)
t_b_end$:
        ; restore used registers 
here 
    _endasm;
}
#endif

The inline assembler code can contain any valid code 
understood by the assembler, this includes any 
assembler directives and comment lines. The assembler 
does not like some characters like ':' or ''' in 
comments. You'll find an 100+ pages assembler manual in 
sdcc/as/doc/asxhtm.html or online at [http://sdcc.svn.sourceforge.net/viewvc/*checkout*/sdcc/trunk/sdcc/as/doc/asxhtm.html] .

The compiler does not do any validation of the code 
within the _asm ... _endasm; keyword pair. Specifically 
it will not know which registers are used and thus 
register pushing/popping has to be done manually. 

It is recommended that each assembly instruction 
(including labels) be placed in a separate line (as the 
example shows). When the --peep-asm command line option 
is used, the inline assembler code will be passed 
through the peephole optimizer. There are only a few 
(if any) cases where this option makes sense, it might 
cause some unexpected changes in the inline assembler 
code. Please go through the peephole optimizer rules 
defined in file SDCCpeeph.def before using this option.

3.12.2 Naked Functions<sub:Naked-Functions>

A special keyword may be associated with a function 
declaring it as _naked. The _naked function modifier 
attribute prevents the compiler from generating prologue
 and epilogue code for that function. This means that 
the user is entirely responsible for such things as 
saving any registers that may need to be preserved, 
selecting the proper register bank, generating the 
return instruction at the end, etc. Practically, this 
means that the contents of the function must be written 
in inline assembler. This is particularly useful for 
interrupt functions, which can have a large (and often 
unnecessary) prologue/epilogue. For example, compare 
the code generated by these two functions:

volatile data unsigned char counter;

void 
simpleInterrupt(void) __interrupt (1)
{
    counter++;
}

void 
nakedInterrupt(void) __interrupt (2) __naked
{
    _asm
      inc     
_counter ; does not change flags, no need to save psw
      reti    
; MUST explicitly include ret or reti in _naked function.
    _endasm;

}

For an 8051 target, the generated simpleInterrupt looks like:

Note, this is an outdated example, recent versions of 
SDCC generate
the same code for simpleInterrupt() and 
nakedInterrupt()!

_simpleInterrupt:
    push    acc
    push    b
    push    dpl
    push    dph
    push    
psw
    mov     psw,#0x00
    inc     _counter
    pop     psw
    pop     dph
    pop     dpl
    pop     b
    pop     acc
    reti

whereas nakedInterrupt looks like:

_nakedInterrupt:
    inc    _counter ; does not change flags, no 
need to save psw
    reti            ; MUST explicitly include ret or 
reti in _naked function

The related directive #pragma exclude allows a more 
fine grained control over pushing & popping the registers.

While there is nothing preventing you from writing C 
code inside a _naked function, there are many ways to 
shoot yourself in the foot doing this, and it is 
recommended that you stick to inline assembler.

3.12.3 Use of Labels within Inline Assembler

SDCC allows the use of in-line assembler with a few 
restrictions regarding labels. All labels defined 
within inline assembler code have to be of the form 
nnnnn$ where nnnnn is a number less than 100 (which 
implies a limit of utmost 100 inline assembler labels 
per function).

This is a slightly more stringent rule than absolutely 
necessary, but stays always on the safe side. Labels in 
the form of nnnnn$ are local labels in the assembler, 
locality of which is confined within two labels of the 
standard form. The compiler uses the same form for 
labels within a function (but starting from 
nnnnn=00100); and places always a standard label at the 
beginning of a function, thus limiting the locality of 
labels within the scope of the function. So, if the 
inline assembler part would be embedded into C-code, an 
improperly placed non-local label in the assembler 
would break up the reference space for labels created 
by the compiler for the C-code, leading to an 
assembling error.

The numeric part of local labels does not need to have 
5 digits (although this is the form of labels output by 
the compiler), any valid integer will do. Please refer 
to the assemblers documentation for further details.
 

_asm 
    mov     b,#10 
00001$: 
    djnz    b,00001$ 
_endasm ;

Inline assembler code cannot reference any C-labels, 
however it can reference labels defined by the inline 
assembler, e.g.:

foo() { 
    /* some c code */ 
    _asm 
      ; some assembler code 
      
ljmp 0003$ 
    _endasm; 
    /* some more c code */ 
clabel:  /* 
inline assembler cannot reference this label */ 

Here, the C-label clabel is translated by the compiler 
into a local label, so the locality of labels within 
the function is not broken.
    
_asm
    0003$: ;label (can be referenced by inline 
assembler only) 
    _endasm ; 
    /* some more c code */
}

In other words inline assembly code can access labels 
defined in inline assembly within the scope of the 
function. The same goes the other way, i.e. labels 
defines in inline assembly can not be accessed by C statements.

3.13 Interfacing with Assembler Code

3.13.1 Global Registers used for Parameter Passing

The compiler always uses the global registers DPL, DPH, B
 and ACC to pass the first (non-bit) parameter to a 
function, and also to pass the return value of 
function; according to the following scheme: one byte 
return value in DPL, two byte value in DPL (LSB) and 
DPH (MSB). three byte values (generic pointers) in DPH, 
DPL and B, and four byte values in DPH, DPL, B and ACC. 
Generic pointers contain type of accessed memory in B: 
0x00 -- xdata/far, 0x40 -- idata/near -- , 0x60 -- 
pdata, 0x80 -- code.

The second parameter onwards is either allocated on the 
stack (for reentrant routines or if --stack-auto is 
used) or in data/xdata memory (depending on the memory model).

Bit parameters are passed in a virtual register called 
'bits' in bit-addressable space for reentrant functions 
or allocated directly in bit memory otherwise.

Functions (with two or more parameters or bit 
parameters) that are called through function pointers 
must therefor be reentrant so the compiler knows how to 
pass the parameters.

3.13.2 Registers usage

Unless the called function is declared as _naked, or 
the --callee-saves/--all-callee-saves command line 
option or the corresponding callee_saves pragma are 
used, the caller will save the registers (R0-R7) around 
the call, so the called function can destroy they 
content freely.

If the called function is not declared as _naked, the 
caller will swap register banks around the call, if 
caller and callee use different register banks (having 
them defined by the _using modifier). 

The called function can also use DPL, DPH, B and ACC 
observing that they are used for parameter/return value passing.

3.13.3 Assembler Routine (non-reentrant)

In the following example the function c_func calls an 
assembler routine asm_func, which takes two parameters.

extern int asm_func(unsigned char, unsigned char);

int 
c_func (unsigned char i, unsigned char j)
{
    return asm_func(i,j);
}


int main()
{
    return c_func(10,9);
}

The corresponding assembler function is:

.globl _asm_func_PARM_2 
        .globl _asm_func 
        .area OSEG 

_asm_func_PARM_2:
        .ds    1 
        .area CSEG 
_asm_func: 
        mov    
a,dpl 
        add    a,_asm_func_PARM_2 
        mov    dpl,a 
        mov    dph,#0x00 
        ret

The parameter naming convention is 
_<function_name>_PARM_<n>, where n is the parameter 
number starting from 1, and counting from the left. The 
first parameter is passed in DPH, DPL, B and ACC 
according to the description above. The variable name 
for the second parameter will be _<function_name>_PARM_2.


Assemble the assembler routine with the following command:


asx8051 -losg asmfunc.asm

Then compile and link the 
assembler routine to the C source file with the 
following command:

sdcc cfunc.c asmfunc.rel

3.13.4 Assembler Routine (reentrant)

In this case the second parameter onwards will be 
passed on the stack, the parameters are pushed from 
right to left i.e. before the call the second leftmost 
parameter will be on the top of the stack (the leftmost 
parameter is passed in registers). Here is an example:

extern int asm_func(unsigned char, unsigned char, 
unsigned char) reentrant;

int c_func (unsigned char i, 
unsigned char j, unsigned char k) reentrant 
{ 
    return 
asm_func(i,j,k); 
} 

int main() 
{ 
    return c_func(10,9,8); 
}

The corresponding (unoptimized) assembler routine is:

.globl _asm_func 
_asm_func: 
    push _bp 
    mov  _bp,sp      ;stack 
contains: _bp, return address, second parameter, third parameter
    
mov  r2,dpl
    mov  a,_bp
    add  a,#0xfd     ;calculate pointer to the 
second parameter
    mov  r0,a 
    mov  a,_bp 
    add  a,#0xfc     ;calculate 
pointer to the rightmost parameter
    mov  r1,a 
    mov  a,@r0
    add  a,@r1
    add  a,r2        
;calculate the result (= sum of all three parameters)
    mov  dpl,a       
;return value goes into dptr (cast into int)
    mov  
dph,#0x00 
    mov  sp,_bp 
    pop  _bp 
    ret

The compiling and linking procedure remains the same, 
however note the extra entry & exit linkage required 
for the assembler code, _bp is the stack frame pointer 
and is used to compute the offset into the stack for 
parameters and local variables.



3.14 int (16 bit) and long (32 bit) Support

For signed & unsigned int (16 bit) and long (32 bit) 
variables, division, multiplication and modulus 
operations are implemented by support routines. These 
support routines are all developed in ANSI-C to 
facilitate porting to other MCUs, although some model 
specific assembler optimizations are used. The 
following files contain the described routines, all of 
them can be found in <installdir>/share/sdcc/lib.


+-----------------+--------------------------------------------+
| 

Function      | 

Description                              |
+-----------------+--------------------------------------------+
+-----------------+--------------------------------------------+
| 

_mulint.c     | 

16 bit multiplication                    |
+-----------------+--------------------------------------------+
| 

_divsint.c    | 

 signed 16 bit division (calls _divuint) |
+-----------------+--------------------------------------------+
| 

_divuint.c    | 

 unsigned 16 bit division                |
+-----------------+--------------------------------------------+
| 

_modsint.c    | 

signed 16 bit modulus (calls _moduint)   |
+-----------------+--------------------------------------------+
| 

_moduint.c    | 

unsigned 16 bit modulus                  |
+-----------------+--------------------------------------------+
| 

_mullong.c    | 

32 bit multiplication                    |
+-----------------+--------------------------------------------+
| 

_divslong.c   | 

 signed 32 division (calls _divulong)    |
+-----------------+--------------------------------------------+
| 

_divulong.c   | 

unsigned 32 division                     |
+-----------------+--------------------------------------------+
| 

_modslong.c   | 

 signed 32 bit modulus (calls _modulong) |
+-----------------+--------------------------------------------+
| 

_modulong.c   | 

unsigned 32 bit modulus                  |
+-----------------+--------------------------------------------+



Since they are compiled as non-reentrant, interrupt 
service routines should not do any of the above 
operations. If this is unavoidable then the above 
routines will need to be compiled with the --stack-auto 
option, after which the source program will have to be 
compiled with --int-long-reent option. Notice that you 
don't have to call these routines directly. The 
compiler will use them automatically every time an 
integer operation is required.

3.15 Floating Point Support

SDCC supports IEEE (single precision 4 bytes) floating 
point numbers. The floating point support routines are 
derived from gcc's floatlib.c and consist of the 
following routines:


+----------------+--------------------------------------------------+
| 

Function     | 

Description                                    |
+----------------+--------------------------------------------------+
+----------------+--------------------------------------------------+
| 

_fsadd.c     | 

add floating point numbers                     |
+----------------+--------------------------------------------------+
| 

_fssub.c     | 

subtract floating point numbers                |
+----------------+--------------------------------------------------+
| 

_fsdiv.c     | 

divide floating point numbers                  |
+----------------+--------------------------------------------------+
| 

_fsmul.c     | 

multiply floating point numbers                |
+----------------+--------------------------------------------------+
| 

_fs2uchar.c  | 

convert floating point to unsigned char        |
+----------------+--------------------------------------------------+
| 

_fs2char.c   | 

convert floating point to signed char          |
+----------------+--------------------------------------------------+
| 

_fs2uint.c   | 

convert floating point to unsigned int         |
+----------------+--------------------------------------------------+
| 

_fs2int.c    | 

convert floating point to signed int           |
+----------------+--------------------------------------------------+
| 

_fs2ulong.c  | 

convert floating point to unsigned long        |
+----------------+--------------------------------------------------+
| 

_fs2long.c   | 

convert floating point to signed long          |
+----------------+--------------------------------------------------+
| 

_uchar2fs.c  | 

convert unsigned char to floating point        |
+----------------+--------------------------------------------------+
| 

_char2fs.c   | 

convert char to floating point number          |
+----------------+--------------------------------------------------+
| 

_uint2fs.c   | 

convert unsigned int to floating point         |
+----------------+--------------------------------------------------+
| 

_int2fs.c    | 

convert int to floating point numbers          |
+----------------+--------------------------------------------------+
| 

_ulong2fs.c  | 

convert unsigned long to floating point number |
+----------------+--------------------------------------------------+
| 

_long2fs.c   | 

convert long to floating point number          |
+----------------+--------------------------------------------------+



These support routines are developed in ANSI-C so there 
is room for space and speed improvement

These floating point routines (not sinf(), cosf(), ...) 
for the mcs51 are implemented in assembler. 
. Note if all these routines are used simultaneously 
the data space might overflow. For serious floating 
point usage the large model might be needed. Also 
notice that you don't have to call this routines 
directly. The compiler will use them automatically 
every time a floating point operation is required.



3.16 Library Routines

<pending: this is messy and incomplete - a little more 
information is in sdcc/doc/libdoc.txt >

3.16.1 Compiler support routines (_gptrget, _mulint etc.)

3.16.2 Stdclib functions (puts, printf, strcat etc.)

3.16.2.1 <stdio.h>

  getchar(), putchar()

As usual on embedded systems you have to provide your 
own getchar() and putchar() routines. SDCC does not 
know whether the system connects to a serial line with 
or without handshake, LCD, keyboard or other device. 
And whether a lf to crlf conversion within putchar() is 
intended. You'll find examples for serial routines f.e. 
in sdcc/device/lib. For the mcs51 this minimalistic 
polling putchar() routine might be a start:

void putchar (char c) { 
    while (!TI)    /* assumes UART is 
initialized */
        ;
    TI = 0;
    SBUF = c;
}

  printf()

The default printf() implementation in printf_large.c 
does not support float (except on ds390). To enable 
this recompile it with the option -DUSE_FLOATS=1 on the 
command line. Use --model-large for the mcs51 port, 
since this uses a lot of memory.

If you're short on code memory you might want to use 
printf_small() instead of printf(). For the mcs51 there 
additionally are assembly versions printf_tiny() 
(subset of printf using less than 270 bytes) and printf_fast()
 and printf_fast_f() (floating-point aware version of 
printf_fast) which should fit the requirements of many 
embedded systems (printf_fast() can be customized by 
unsetting #defines to not support long variables and 
field widths). Be sure to use only one of these printf 
options within a project.


Feature matrix of different printf options on mcs51.

+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+------------------------+----------------------------+-------------------+------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------+
| 

mcs51                                                                                                                                                            |     

printf      | 

printf USE_FLOATS=1  |      

printf_small        |  

printf_fast    |                                  

printf_fast_f                                   |                                      

printf_tiny                                     |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+------------------------+----------------------------+-------------------+------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------+
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+------------------------+----------------------------+-------------------+------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------+
| 

filename                                                                                                                                                         | 

printf_large.c  |   

printf_large.c     |        

printfl.c         | 

printf_fast.c   |                                 

printf_fast_f.c                                  |                                     

printf_tiny.c                                    |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+------------------------+----------------------------+-------------------+------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------+
| 

"Hello World" size

small / large                                                                                                                                |  

1.7k / 2.4k    |     

4.3k / 5.6k      |       

1.2k / 1.8k        |  

1.3k / 1.3k    |                                   

1.9k / 1.9k                                    |                                     

0.44k / 0.44k                                    |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+------------------------+----------------------------+-------------------+------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------+
| 

code size

small / large                                                                                                                                         |  

1.4k / 2.0k    |     

2.8k / 3.7k      | 

0.45k / 0.47k (+ _ltoa)  |  

1.2k / 1.2k    |                                   

1.6k / 1.6k                                    |                                     

0.26k / 0.26k                                    |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+------------------------+----------------------------+-------------------+------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------+
| 

formats                                                                                                                                                          |    

cdiopsux     |      

cdfiopsux       |          

cdosx           |     

cdsux       |                                      

cdfsux                                      |                                         

cdsux                                        |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+------------------------+----------------------------+-------------------+------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------+
| 

long (32 bit) support                                                                                                                                            |       

x         |          

x           |            

x             |       

x         |                                        

x                                         |                                           

-                                          |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+------------------------+----------------------------+-------------------+------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------+
| 

byte arguments on stack                                                                                                                                          |       

b         |          

b           |            

-             |       

-         |                                        

-                                         |                                           

-                                          |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+------------------------+----------------------------+-------------------+------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------+
| 

float format                                                                                                                                                     |       

-         |         

%f           |            

-             |       

-         | 

%f

Range limited to +/- 4294967040, precision limited to 8 
digits past decimal |                                           

-                                          |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+------------------------+----------------------------+-------------------+------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------+
| 

float formats %e %g                                                                                                                                              |       

-         |          

-           |            

-             |       

-         |                                        

-                                         |                                           

-                                          |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+------------------------+----------------------------+-------------------+------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------+
| 

field width                                                                                                                                                      |       

x         |          

x           |            

-             |       

x         |                                        

x                                         |                                           

-                                          |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+------------------------+----------------------------+-------------------+------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------+
| 

string speed

Execution time of printf("%s%c%s%c%c%c", "Hello", ' ', 
"World", '!', '\r', '\n'); standard 8051 @ 22.1184 MHz, 
empty putchar()
,

small / large  | 

1.52 / 2.59 ms  |   

1.53 / 2.62 ms     |     

0.92 / 0.93 ms       | 

0.45 / 0.45 ms  |                                  

0.46 / 0.46 ms                                  |                                    

0.45 / 0.45 ms                                    |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+------------------------+----------------------------+-------------------+------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------+
| 

int speed

Execution time of printf("%d", -12345); standard 8051 @ 
22.1184 MHz, empty putchar()
,

small / large                                                | 

3.01 / 3.61 ms  |   

3.01 / 3.61 ms     |     

3.51 / 18.13 ms      | 

0.22 / 0.22 ms  |                                  

0.23 / 0.23 ms                                  |  

0.25 / 0.25 ms

printf_tiny integer speed is data dependent, worst case 
is 0.33 ms |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+------------------------+----------------------------+-------------------+------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------+
| 

long speed

Execution time of printf("%ld", -123456789); standard 
8051 @ 22.1184 MHz, empty putchar()
,

small / large                                          | 

5.37 / 6.31 ms  |   

5.37 / 6.31 ms     |     

8.71 / 40.65 ms      | 

0.40 / 0.40 ms  |                                  

0.40 / 0.40 ms                                  |                                           

-                                          |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+------------------------+----------------------------+-------------------+------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------+
| 

float speed

Execution time of printf("%.3f", -12345.678); standard 
8051 @ 22.1184 MHz, empty putchar()
,

small / large                                        |       

-         |   

7.49 / 22.47 ms    |            

-             |       

-         |                                  

1.04 / 1.04 ms                                  |                                           

-                                          |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------+------------------------+----------------------------+-------------------+------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------+


3.16.2.2 <malloc.h>

As of SDCC 2.6.2 you no longer need to call an 
initialization routine before using dynamic memory allocation
 and a default heap space of 1024 bytes is provided for 
malloc to allocate memory from. If you need a different 
heap size you need to recompile _heap.c with the 
required size defined in HEAP_SIZE. It is recommended 
to make a copy of this file into your project directory 
and compile it there with:

sdcc -c _heap.c -D HEAD_SIZE=2048

And then link it with:

sdcc main.rel _heap.rel

3.16.3 Math functions (sinf, powf, sqrtf etc.)

3.16.3.1 <math.h>

See definitions in file <math.h>.

3.16.4 Other libraries

Libraries included in SDCC should have a license at 
least as liberal as the GNU Lesser General Public License
 LGPL.



If you have ported some library or want to share 
experience about some code which f.e. falls into any of 
these categories Busses (I^{\textrm{2}}C, CAN, Ethernet, Profibus, 
Modbus, USB, SPI, JTAG ...), Media (IDE, Memory cards, 
eeprom, flash...), En-/Decryption, Remote debugging, 
Realtime kernel, Keyboard, LCD, RTC, FPGA, PID then the 
sdcc-user mailing list [http://sourceforge.net/mail/?group_id=599] would certainly like to hear 
about it.

Programmers coding for embedded systems are not 
especially famous for being enthusiastic, so don't 
expect a big hurray but as the mailing list is 
searchable these references are very valuable. Let's 
help to create a climate where information is shared.



3.17 Memory Models

3.17.1 MCS51 Memory Models

3.17.1.1 Small, Medium and Large

SDCC allows three memory models for MCS51 code, small, 
medium and large. Modules compiled with different 
memory models should never be combined together or the 
results would be unpredictable. The library routines 
supplied with the compiler are compiled as small, 
medium and large. The compiled library modules are 
contained in separate directories as small, medium and 
large so that you can link to the appropriate set.

When the medium or large model is used all variables 
declared without a storage class will be allocated into 
the external ram, this includes all parameters and 
local variables (for non-reentrant functions). When the 
small model is used variables without storage class are 
allocated in the internal ram.

Judicious usage of the processor specific storage classes
 and the 'reentrant' function type will yield much more 
efficient code, than using the large model. Several 
optimizations are disabled when the program is compiled 
using the large model, it is therefore recommended that 
the small model be used unless absolutely required.

3.17.1.2 External Stack<sub:External-Stack>

The external stack (--xstack option) is located in pdata
 memory (usually at the start of the external ram 
segment) and uses all unused space in pdata (max. 256 
bytes). When --xstack option is used to compile the 
program, the parameters and local variables of all 
reentrant functions are allocated in this area. This 
option is provided for programs with large stack space 
requirements. When used with the --stack-auto option, 
all parameters and local variables are allocated on the 
external stack (note: support libraries will need to be 
recompiled with the same options. There is a predefined 
target in the library makefile).

The compiler outputs the higher order address byte of 
the external ram segment into port P2 (see also section [sub:MCS51-variants]
), therefore when using the External Stack option, this 
port may not be used by the application program.

3.17.2 DS390 Memory Model

The only model supported is Flat 24. This generates 
code for the 24 bit contiguous addressing mode of the 
Dallas DS80C390 part. In this mode, up to four meg of 
external RAM or code space can be directly addressed. 
See the data sheets at www.dalsemi.com for further 
information on this part.

Note that the compiler does 
not generate any code to place the processor into 24 
bitmode (although tinibios in the ds390 libraries will 
do that for you). If you don't use tinibios, the boot 
loader or similar code must ensure that the processor 
is in 24 bit contiguous addressing mode before calling 
the SDCC startup code.

Like the --model-large option, 
variables will by default be placed into the XDATA 
segment. 

Segments may be placed anywhere in the 4 meg 
address space using the usual --*-loc options. Note 
that if any segments are located above 64K, the -r flag 
must be passed to the linker to generate the proper 
segment relocations, and the Intel HEX output format 
must be used. The -r flag can be passed to the linker 
by using the option -Wl-r on the SDCC command line. 
However, currently the linker can not handle code 
segments > 64k.

3.18 Pragmas<sec:Pragmas>

Pragmas are used to turn on and/or off certain compiler 
options. Some of them are closely related to 
corresponding command-line options (see section [sec:Command-Line-Options]).

Pragmas should be placed before and/or after a 
function, placing pragmas inside a function body could 
have unpredictable results.

SDCC supports the following 
#pragma directives:

* save - this will save most current options to the 
  save/restore stack. See #pragma restore.

* restore - will restore saved options from the last 
  save. saves & restores can be nested. SDCC uses a 
  save/restore stack: save pushes current options to 
  the stack, restore pulls current options from the 
  stack. See #pragma save.


* callee_saves function1[,function2[,function3...]] <ite:callee_saves-function1[,function2[,function3...]]-->- 
  The compiler by default uses a caller saves 
  convention for register saving across function calls, 
  however this can cause unnecessary register pushing 
  and popping when calling small functions from larger 
  functions. This option can be used to switch off the 
  register saving convention for the function names 
  specified. The compiler will not save registers when 
  calling these functions, extra code need to be 
  manually inserted at the entry and exit for these 
  functions to save and restore the registers used by 
  these functions, this can SUBSTANTIALLY reduce code 
  and improve run time performance of the generated 
  code. In the future the compiler (with inter 
  procedural analysis) may be able to determine the 
  appropriate scheme to use for each function call. If -
  -callee-saves command line option is used (see page [lyx:--callee-saves-function1[,function2][,function3]...]
  ), the function names specified in #pragma callee_saves
   is appended to the list of functions specified in 
  the command line.

* exclude none | {acc[,b[,dpl[,dph]]] - The exclude 
  pragma disables the generation of pairs of push/pop 
  instructions in Interrupt Service Routines. The 
  directive should be placed immediately before the ISR 
  function definition and it affects ALL ISR functions 
  following it. To enable the normal register saving 
  for ISR functions use #pragma exclude none. See also 
  the related keyword _naked.

* less_pedantic <ite:less_pedantic>- the compiler will not warn you 
  anymore for obvious mistakes, you're on your own now 
  ;-( . See also the command line option -
  -less-pedantic [lyx:--less-pedantic]. 
More specifically, the following 
  warnings will be disabled: comparison is always 
  [true/false] due to limited range of data type (94); 
  overflow in implicit constant conversion (158); [the 
  (in)famous] conditional flow changed by optimizer: so 
  said EVELYN the modified DOG (110); function 
  '[function name]' must return value (59). 

  Furthermore, warnings of less importance (of PEDANTIC 
  and INFO warning level) are disabled, too, namely: 
  constant value '[]', out of range (81); [left/right] 
  shifting more than size of object changed to zero 
  (116); unreachable code (126); integer overflow in 
  expression (165); unmatched #pragma save and #pragma 
  restore (170); comparison of 'signed char' with 
  'unsigned char' requires promotion to int (185); ISO 
  C90 does not support flexible array members (187); 
  extended stack by [number] bytes for compiler temp(s) 
  :in function '[function name]': [] (114); function 
  '[function name]', # edges [number] , # nodes 
  [number] , cyclomatic complexity [number] (121).

* disable_warning <nnnn> - the compiler will not warn 
  you anymore about warning number <nnnn>.

* nogcse - will stop global common subexpression elimination.

* noinduction - will stop loop induction optimizations.

* noinvariant - will not do loop invariant 
  optimizations. For more details see Loop Invariants 
  in section[sub:Loop-Optimizations].

* noiv - Do not generate interrupt vector table entries 
  for all ISR functions defined after the pragma. This 
  is useful in cases where the interrupt vector table 
  must be defined manually, or when there is a 
  secondary, manually defined interrupt vector table 
  (e.g. for the autovector feature of the Cypress 
  EZ-USB FX2). More elegantly this can be achieved by 
  obmitting the optional interrupt number after the 
  interrupt keyword, see section [sub:Interrupt-Service-Routines] about interrupts.

* nojtbound - will not generate code for boundary value 
  checking, when switch statements are turned into 
  jump-tables (dangerous). For more details see section [sub:'switch'-Statements].

* noloopreverse - Will not do loop reversal optimization

* nooverlay - the compiler will not overlay the 
  parameters and local variables of a function.

* stackauto- See option --stack-auto and section [sec:Parameters-and-Local-Variables] 
  Parameters and Local Variables.

* opt_code_speed - The compiler will optimize code 
  generation towards fast code, possibly at the expense 
  of code size. Currently this has little effect.

* opt_code_size - The compiler will optimize code 
  generation towards compact code, possibly at the 
  expense of code speed. Currently this has little effect.

* opt_code_balanced - The compiler will attempt to 
  generate code that is both compact and fast, as long 
  as meeting one goal is not a detriment to the other 
  (this is the default). 

* std_sdcc89 - Generally follow the C89 standard, but 
  allow SDCC features that conflict with the standard (default).

* std_c89 - Follow the C89 standard and disable SDCC 
  features that conflict with the standard.

* std_sdcc99 - Generally follow the C99 standard, but 
  allow SDCC features that conflict with the standard 
  (incomplete support).

* std_c99 - Follow the C99 standard and disable SDCC 
  features that conflict with the standard (incomplete support).

* codeseg <name>- Use this name (max. 8 characters) for 
  the code segment. See option --codeseg.

* constseg <name>- Use this name (max. 8 characters) 
  for the const segment. See option --constseg.

The preprocessor SDCPP supports the following #pragma directives:

* pedantic_parse_number (+ | -) <ite:pedantic_parse_number>- Pedantic parse 
  numbers so that situations like 0xfe-LO_B(3) are 
  parsed properly and the macro LO_B(3) gets expanded. 
  Default is off. See also the --pedantic-parse-number 
  command line option [lyx:-pedantic-parse-number]. 
Below is an example on how to 
  use this pragma. Note: this functionality is not in 
  conformance with standard!

#pragma pedantic_parse_number +

#define LO_B(x) ((x) & 0xff)


unsigned char foo(void)
{
   unsigned char c=0xfe-LO_B(3);

   
return c;
}


* preproc_asm (+ | -) - switch _asm _endasm block 
  preprocessing on / off. Default is on. You use this 
  prama to define multilines of assembly code. This 
  will prevent the preprocessor from changing the 
  formating required by assembly code. Below is an 
  example on how to use this pragma.

#pragma preproc_asm -
#define MYDELAY _asm
   nop ;my 
assembly comment...
   nop
   nop
_endasm
#pragma preproc_asm +


void foo (void) 
{ 
    ... 
    MYDELAY;
    ... 
} 


* sdcc_hash (+ | -) - Allow "naked" hash in macro 
  definition, for example:
#define DIR_LO(x) #(x & 0xff)

  Default is off. Below is an example on how to use 
  this pragma.

#pragma preproc_asm +
#pragma sdcc_hash +

#define 
ROMCALL(x) \
   mov R6_B3, #(x & 0xff) \
   mov R7_B3, #((x >> 
8) & 0xff) \
   lcall __romcall

...
_asm
ROMCALL(72)
_endasm;
...


Some of the pragmas are intended to be used to turn-on 
or off certain optimizations which might cause the 
compiler to generate extra stack and/or data space to 
store compiler generated temporary variables. This 
usually happens in large functions. Pragma directives 
should be used as shown in the following example, they 
are used to control options and optimizations for a 
given function. 

#pragma save        /* save the current settings */ 
#pragma nogcse
      /* turnoff global subexpression elimination */ 
#pragma 
noinduction /* turn off induction optimizations */ 
int 
foo () 
{ 
    ... 
    /* large code */ 
    ... 
} 
#pragma restore
 /* turn the optimizations back on */

The compiler will generate a warning message when extra 
space is allocated. It is strongly recommended that the 
save and restore pragmas be used when changing options 
for a function.




3.19 Defines Created by the Compiler

The compiler creates the following #defines:


+-----------------------------------------------+-------------------------------------------------------------------------------+
| 

#define                                     | 

Description                                                                 |
+-----------------------------------------------+-------------------------------------------------------------------------------+
+-----------------------------------------------+-------------------------------------------------------------------------------+
| 

SDCC                                        | 

Always defined. Since version 2.5.6 the version number 
as an int (ex. 256) |
+-----------------------------------------------+-------------------------------------------------------------------------------+
| 

SDCC_mcs51 or SDCC_ds390 or SDCC_z80, etc.  | 

depending on the model used (e.g.: -mds390)                                 |
+-----------------------------------------------+-------------------------------------------------------------------------------+
| 

__mcs51, __ds390, __hc08, __z80, etc        | 

depending on the model used (e.g. -mz80)                                    |
+-----------------------------------------------+-------------------------------------------------------------------------------+
| 

SDCC_STACK_AUTO                             | 

when --stack-auto option is used                                            |
+-----------------------------------------------+-------------------------------------------------------------------------------+
| 

SDCC_MODEL_SMALL                            | 

when --model-small is used                                                  |
+-----------------------------------------------+-------------------------------------------------------------------------------+
| 

SDCC_MODEL_MEDIUM                           | 

when --model-medium is used                                                 |
+-----------------------------------------------+-------------------------------------------------------------------------------+
| 

SDCC_MODEL_LARGE                            | 

when --model-large is used                                                  |
+-----------------------------------------------+-------------------------------------------------------------------------------+
| 

SDCC_USE_XSTACK                             | 

when --xstack option is used                                                |
+-----------------------------------------------+-------------------------------------------------------------------------------+
| 

SDCC_STACK_TENBIT                           | 

when -mds390 is used                                                        |
+-----------------------------------------------+-------------------------------------------------------------------------------+
| 

SDCC_MODEL_FLAT24                           | 

when -mds390 is used                                                        |
+-----------------------------------------------+-------------------------------------------------------------------------------+
| 

SDCC_REVISION                               | 

Always defined. SDCC svn revision number                                    |
+-----------------------------------------------+-------------------------------------------------------------------------------+
| 

SDCC_PARMS_IN_BANK1                         | 

when --parms-in-bank1 is used                                               |
+-----------------------------------------------+-------------------------------------------------------------------------------+
| 

SDCC_FLOAT_REENT                            | 

when --float-reent is used                                                  |
+-----------------------------------------------+-------------------------------------------------------------------------------+
| 

SDCC_INT_LONG_REENT                         | 

when --int-long-reent is used                                               |
+-----------------------------------------------+-------------------------------------------------------------------------------+


Notes on supported Processors

4.1 MCS51 variants<sub:MCS51-variants>

MCS51 processors are available from many vendors and 
come in many different flavours. While they might 
differ considerably in respect to Special Function 
Registers the core MCS51 is usually not modified or is 
kept compatible. 

4.1.1 pdata access by SFR 

With the upcome of devices with internal xdata and 
flash memory devices using port P2 as dedicated I/O 
port is becoming more popular. Switching the high byte 
for pdata access which was formerly done by port P2 is 
then achieved by a Special Function Register. In 
well-established MCS51 tradition the address of this 
sfr is where the chip designers decided to put it. 
Needless to say that they didn't agree on a common name 
either. So that the startup code can correctly 
initialize xdata variables, you should define an sfr 
with the name _XPAGE at the appropriate location if the 
default, port P2, is not used for this. Some examples are:

__sfr __at (0x85) _XPAGE; /* Ramtron VRS51 family 
a.k.a. MPAGE */

__sfr __at (0x92) _XPAGE; /* Cypress EZ-USB family, 
Texas Instruments (Chipcon) a.k.a. MPAGE */

__sfr __at (0x91) _XPAGE; /* Infineon (Siemens) C500 
family a.k.a. XPAGE */

__sfr __at (0xaf) _XPAGE; /* some Silicon Labs (Cygnal) 
chips a.k.a. EMI0CN */

__sfr __at (0xaa) _XPAGE; /* some Silicon Labs (Cygnal) 
chips a.k.a. EMI0CN */

For more exotic implementations further customizations 
may be needed. See section [sub:Startup-Code] for other possibilities.

4.1.2 Other Features available by SFR

Some MCS51 variants offer features like Double DPTR, 
multiple DPTR, decrementing DPTR, 16x16 Multiply. These 
are currently not used for the MCS51 port. If you 
absolutely need them you can fall back to inline 
assembly or submit a patch to SDCC.

4.1.3 Bankswitching

Bankswitching (a.k.a. code banking) is a technique to 
increase the code space above the 64k limit of the 8051.

4.1.3.1 Hardware

               +-----------+----------+---------+
  

8000-FFFF  | 

bank1   | 

bank2  | 

bank3 |
               +-----------+----------+---------+
               +-----------                      
  

0000-7FFF  | 

common  |         

          
               +-----------                      
           

SiLabs C8051F120 example            



Usually the hardware uses some sfr (an output port or 
an internal sfr) to select a bank and put it in the 
banked area of the memory map. The selected bank 
usually becomes active immediately upon assignment to 
this sfr and when running inside a bank it will switch 
out this code it is currently running. Therefor you 
cannot jump or call directly from one bank to another 
and need to use a so-called trampoline in the common 
area. For SDCC an example trampoline is in crtbank.asm 
and you may need to change it to your 8051 derivative 
or schematic. The presented code is written for the C8051F120.


When calling a banked function SDCC will put the LSB of 
the functions address in register R0, the MSB in R1 and 
the bank in R2 and then call this trampoline 
__sdcc_banked_call. The current selected bank is saved 
on the stack, the new bank is selected and an indirect 
jump is made. When the banked function returns it jumps 
to __sdcc_banked_ret which restores the previous bank 
and returns to the caller.

4.1.3.2 Software

When writing banked software using SDCC you need to use 
some special keywords and options. You also need to 
take over a bit of work from the linker.

To create a 
function that can be called from another bank it 
requires the keyword banked. The caller must see this 
in the prototype of the callee and the callee needs it 
for a proper return. Called functions within the same 
bank as the caller do not need the banked keyword nor 
do functions in the common area. Beware: SDCC does not 
know or check if functions are in the same bank. This 
is your responsibility!

Normally all functions you write 
end up in the segment CSEG. If you want a function 
explicitly to reside in the common area put it in 
segment HOME. This applies for instance to interrupt 
service routines as they should not be banked.

Functions that need to be in a switched bank must be 
put in a named segment. The name can be mostly anything 
upto eight characters (e.g. BANK1). To do this you 
either use --codeseg BANK1 (See [lyx:-codeseg]) on the command line 
when compiling or #pragma codeseg BANK1 (See [sec:Pragmas]) at the 
top of the C source file. The segment name always 
applies to the whole source file and generated object 
so functions for different banks need to be defined in 
different source files.

When linking your objects you 
need to tell the linker where to put your segments. To 
do this you use the following command line option to 
SDCC: -Wl-b BANK1=0x18000 (See [lyx:-Wl option]). This sets the virtual 
start address of this segment. It sets the banknumber 
to 0x01 and maps the bank to 0x8000 and up. The linker 
will not check for overflows, again this is your responsibility.





4.2 DS400 port

The DS80C400 microcontroller has a rich set of 
peripherals. In its built-in ROM library it includes 
functions to access some of the features, among them is 
a TCP stack with IP4 and IP6 support. Library headers 
(currently in beta status) and other files are provided 
at [ftp://ftp.dalsemi.com/pub/tini/ds80c400/c_libraries/sdcc/index.html]. 



4.3 The Z80 and gbz80 port

SDCC can target both the Zilog Z80 and the Nintendo 
Gameboy's Z80-like gbz80. The Z80 port is passed 
through the same regressions tests (see section [sec:Quality-control]) as 
the MCS51 and DS390 ports, so floating point support, 
support for long variables and bitfield support is 
fine. See mailing lists and forums about interrupt routines.

As always, the code is the authoritative reference - 
see z80/ralloc.c and z80/gen.c. The stack frame is 
similar to that generated by the IAR Z80 compiler. IX 
is used as the base pointer, HL and IY are used as a 
temporary registers, and BC and DE are available for 
holding variables. Return values for the Z80 port are 
stored in L (one byte), HL (two bytes), or DEHL (four 
bytes). The gbz80 port use the same set of registers 
for the return values, but in a different order of 
significance: E (one byte), DE (two bytes), or HLDE 
(four bytes).



4.4 The HC08 port

The port to the Freescale/Motorola HC08 family has been 
added in October 2003, and is still undergoing some 
basic development. The code generator is complete, but 
the register allocation is still quite unoptimized. 
Some of the SDCC's standard C library functions have 
embedded non-HC08 inline assembly and so are not yet usable.

The HC08 port passes the regression test suite (see 
section [sec:Quality-control]).



4.5 The PIC14 port

The PIC14 port adds support for Microchip^{\text{TM}} PIC^{\text{TM}} MCUs with 
14 bit wide instructions. This port is not yet mature 
and still lacks many features. However, it can work for 
simple code.

Currently supported devices include:

12F: 629, 635, 675, 683

16C: 432, 433

16C: 554, 557, 558

16C: 62, 620, 620a, 621, 621a, 622, 622a, 63a, 65b

16C: 71, 710, 711, 715, 717, 72, 73b, 745, 74b, 765, 
770, 771, 773, 774, 781, 782

16C: 925, 926

16CR: 620a, 73, 74, 76, 77

16F: 616, 627, 627a, 628, 628a, 630, 636, 639, 648, 
648a, 676, 684, 685, 687, 688, 689, 690

16F: 716, 72, 73, 737, 74, 747, 76, 767, 77, 777, 785

16F: 818, 819, 84, 84a, 87, 870, 871, 872, 873, 873a, 
874, 874a, 876, 876a, 877, 877a, 88, 886, 887

16F: 913, 914, 916, 917, 946

26HV: 626, 785

An up-to-date list of currently supported devices can 
be obtained via sdcc -mpic14 -phelp foo.c (foo.c must exist...).

4.5.1 PIC Code Pages and Memory Banks

The linker organizes allocation for the code page and 
RAM banks. It does not have intimate knowledge of the 
code flow. It will put all the code section of a single 
.asm file into a single code page. In order to make use 
of multiple code pages, separate asm files must be 
used. The compiler assigns all static functions of a 
single .c file into the same code page.

To get the best 
results, follow these guidelines:

1. Make local functions static, as non static functions 
  require code page selection overhead.
Due to the way 
  sdcc handles functions, place called functions prior 
  to calling functions in the file wherever possible: 
  Otherwise sdcc will insert unneccessary pagesel 
  directives around the call, believing that the called 
  function is externally defined.

2. For devices that have multiple code pages it is more 
  efficient to use the same number of files as pages: 
  Use up to 4 separate .c files for the 16F877, but 
  only 2 files for the 16F874. This way the linker can 
  put the code for each file into different code pages 
  and there will be less page selection overhead.

3. And as for any 8 bit micro (especially for PIC14 as 
  they have a very simple instruction set), use 
  `unsigned char' wherever possible instead of `int'.

4.5.2 Adding New Devices to the Port 

Adding support for a new 14bit PIC MCU requires the 
following steps:

1. Create a new device description.
Each device is 
  described in two files: pic16f*.h and pic16f*.c. 
  These files primarily define SFRs, structs to access 
  their bits, and symbolic configuration options. Both 
  files can be generated from gputils' .inc files using 
  the perl script support/scripts/inc2h.pl. This file 
  also contains further instructions on how to proceed.

2. Copy the .h file into SDCC's include path and either 
  add the .c file to your project or copy it to 
  device/lib/pic/libdev. Afterwards, rebuild and 
  install the libraries.

3. Edit pic14devices.txt in SDCC's include path 
  (device/include/pic/ in the source tree or 
  /usr/local/share/sdcc/include/pic after installation).

  You need to add a device specification here to make 
  the memory layout (code banks, RAM, aliased memory 
  regions, ...) known to the compiler. Probably you can 
  copy and modify an existing entry. The file format is 
  documented at the top of the file.

4.5.3 Interrupt Code

For the interrupt function, use the keyword `__interrupt'
 with level number of 0 (PIC14 only has 1 interrupt so 
this number is only there to avoid a syntax error - it 
ought to be fixed). E.g.:

void Intr(void) __interrupt 0
{
  T0IF = 0; /* Clear timer 
interrupt */
}

4.5.4 Linking and Assembling

For assembling you can use either GPUTILS' gpasm.exe or 
MPLAB's mpasmwin.exe. GPUTILS are available from [http://sourceforge.net/projects/gputils]. For 
linking you can use either GPUTILS' gplink or MPLAB's 
mplink.exe. If you use MPLAB and an interrupt function 
then the linker script file vectors section will need 
to be enlarged to link with mplink.

Here is a Makefile 
using GPUTILS:

.c.o:
        sdcc -V -mpic14 -p16f877 -c $< 

$(PRJ).hex: $(OBJS) 
        
gplink -m -s $(PRJ).lkr -o $(PRJ).hex $(OBJS) libsdcc.lib

Here is a Makefile using MPLAB:

.c.o: 
        sdcc -S -V -mpic14 -p16f877 $< 
        mpasmwin /q /o $*.asm


$(PRJ).hex: $(OBJS) 
        mplink /v $(PRJ).lkr /m $(PRJ).map 
/o $(PRJ).hex $(OBJS) libsdcc.lib

Please note that indentations within a Makefile have to 
be done with a tabulator character.

4.5.5 Command-Line Options

Besides the switches common to all SDCC backends, the 
PIC14 port accepts the following options (for an 
updated list see sdcc --help):

  --debug-xtra emit debug info in assembly output

  --no-pcode-opt disable (slightly faulty) optimization 
  on pCode

  --stack-loc sets the lowest address of the argument 
  passing stack (defaults to a suitably large shared 
  databank to reduce BANKSEL overhead)

  --stack-size sets the size if the argument passing 
  stack (default: 16, minimum: 4)

4.5.6 Environment Variables

The PIC14 port recognizes the following environment variables:

  SDCC_PIC14_SPLIT_LOCALS If set and not empty, sdcc 
  will allocate each temporary register (the ones 
  called r0xNNNN) in a section of its own. By default 
  (if this variable is unset), sdcc tries to cluster 
  registers in sections in order to reduce the BANKSEL 
  overhead when accessing them.

4.5.7 The Library

The PIC14 library currently only contains support 
routines required by the compiler to implement 
multiplication, division, and floating point support. 
No libc-like replacement is available at the moment, 
though many of the common sdcc library sources (in 
device/lib) should also compile with the PIC14 port.

4.5.7.1 error: missing definition for symbol ``__gptrget1''

The PIC14 port uses library routines to provide more 
complex operations like multiplication, 
division/modulus and (generic) pointer dereferencing. 
In order to add these routines to your project, you 
must link with PIC14's libsdcc.lib. For single source 
file projects this is done automatically, more complex 
projects must add libsdcc.lib to the linker's 
arguments. Make sure you also add an include path for 
the library (using the -I switch to the linker)!

4.5.7.2 Processor mismatch in file ``XXX''.

This warning can usually be ignored due to the very 
good compatibility amongst 14bit PIC devices.

You might also consider recompiling the library for 
your specific device by changing the ARCH=p16f877 
(default target) entry in device/lib/pic/Makefile.in 
and device/lib/pic/Makefile to reflect your device. 
This might even improve performance for smaller devices 
as unneccesary BANKSELs might be removed.

4.5.8 Known Bugs

4.5.8.1 Function arguments

Functions with variable argument lists (like printf) 
are not yet supported. Similarly, taking the address of 
the first argument passed into a function does not 
work: It is currently passed in WREG and has no address...

4.5.8.2 Regression tests fail

Though the small subset of regression tests in 
src/regression passes, SDCC regression test suite does 
not, indicating that there are still major bugs in the 
port. However, many smaller projects have successfully 
used SDCC in the past...




4.6 The PIC16 port

The PIC16 port adds support for Microchip^{\text{TM}} PIC^{\text{TM}} MCUs with 
16 bit wide instructions. Currently this family of 
microcontrollers contains the PIC18Fxxx and PIC18Fxxxx; 
devices supported by the port include:

18F: 242, 248, 252, 258, 442, 448, 452, 458

18F: 1220, 1320

18F: 2220, 2221, 2320, 2321, 2331, 2431, 2455, 24j10, 
2525, 2550, 25j10, 2620

18F: 4220, 4221, 4320, 4321, 4331, 4431, 4455, 44j10, 
4520, 4525, 4550, 45j10, 4620

18F: 6520, 6620, 6680, 6720

18F: 8520, 8620, 8680, 8720

4.6.1 Global Options

PIC16 port supports the standard command line arguments 
as supposed, with the exception of certain cases that 
will be mentioned in the following list:

  --callee-saves See --all-callee-saves

  --fommit-frame-pointer Frame pointer will be omitted 
  when the function uses no local variables.

4.6.2 Port Specific Options

The port specific options appear after the global 
options in the sdcc --help output.

4.6.2.1 Code Generation Options

These options influence the generated assembler code.

  --pstack-model=[model] Used in conjuction with the 
  command above. Defines the stack model to be used, 
  valid stack models are:

  small Selects small stack model. 8 bit stack and 
  frame pointers. Supports 256 bytes stack size.

  large Selects large stack model. 16 bit stack and 
  frame pointers. Supports 65536 bytes stack size.

  --pno-banksel Do not generate BANKSEL assembler directives.

  --extended Enable extended instruction set/literal 
  offset addressing mode. Use with care!

4.6.2.2 Optimization Options

  --obanksel=n Set optimization level for inserting BANKSELs.


  0 no optimization

  1 checks previous used register and if it is the same 
  then does not emit BANKSEL, accounts only for labels.

  2 tries to check the location of (even different) 
  symbols and removes BANKSELs if they are in the same 
  bank. 
Important: There might be problems if the 
  linker script has data sections across bank borders!

  --denable-peeps Force the usage of peepholes. Use 
  with care.

  --optimize-goto Try to use (conditional) BRA instead 
  of GOTO.

  --optimize-cmp Try to optimize some compares.

  --optimize-df Analyze the dataflow of the generated 
  code and improve it.

4.6.2.3 Assembling Options

  --asm= Sets the full path and name of an external 
  assembler to call.

  --mplab-comp MPLAB compatibility option. Currently 
  only suppresses special gpasm directives.

4.6.2.4 Linking Options

  --link= Sets the full path and name of an external 
  linker to call.

  --preplace-udata-with=[kword] Replaces the default 
  udata keyword for allocating unitialized data 
  variables with [kword]. Valid keywords are: 
  "udata_acs", "udata_shr", "udata_ovr".

  --ivt-loc=n Place the interrupt vector table at 
  address n. Useful for bootloaders.

  --nodefaultlibs Do not link default libraries when linking.

  --use-crt= Use a custom run-time module instead of 
  the defaults.

  --no-crt Don't link the default run-time modules

4.6.2.5 Debugging Options

Debugging options enable extra debugging information in 
the output files.

  --debug-xtra Similar to --debug, but dumps more information.

  --debug-ralloc Force register allocator to dump 
  <source>.d file with debugging information. <source> 
  is the name of the file being compiled.

  --pcode-verbose Enable pcode debugging information in 
  translation.

  --calltree Dump call tree in .calltree file.

  --gstack Trace push/pops for stack pointer overflow.

4.6.3 Enviroment Variables

There is a number of enviromental variables that can be 
used when running SDCC to enable certain optimizations 
or force a specific program behaviour. these variables 
are primarily for debugging purposes so they can be 
enabled/disabled at will.

Currently there is only two such variables available:

  OPTIMIZE_BITFIELD_POINTER_GET When this variable 
  exists, reading of structure bitfields is optimized 
  by directly loading FSR0 with the address of the 
  bitfield structure. Normally SDCC will cast the 
  bitfield structure to a bitfield pointer and then 
  load FSR0. This step saves data ram and code space 
  for functions that make heavy use of bitfields. 
  (i.e., 80 bytes of code space are saved when 
  compiling malloc.c with this option). 

  NO_REG_OPT Do not perform pCode registers 
  optimization. This should be used for debugging 
  purposes. If bugs in the pcode optimizer are found, 
  users can benefit from temporarily disabling the 
  optimizer until the bug is fixed.

4.6.4 Preprocessor Macros

PIC16 port defines the following preprocessor macros 
while translating a source.

+--------------------+--------------------------------------------------------------------------------------------+
|      

Macro       |                                       

Description                                        |
+--------------------+--------------------------------------------------------------------------------------------+
+--------------------+--------------------------------------------------------------------------------------------+
|   

SDCC_pic16     |                                   

Port identification                                    |
+--------------------+--------------------------------------------------------------------------------------------+
|     

__pic16      |                           

Port identification (same as above)                            |
+--------------------+--------------------------------------------------------------------------------------------+
|   

pic18fxxxx     | 

MCU Identification. xxxx is the microcontrol 
identification number, i.e. 452, 6620, etc |
+--------------------+--------------------------------------------------------------------------------------------+
|    

__18Fxxxx     |                            

MCU Identification (same as above)                            |
+--------------------+--------------------------------------------------------------------------------------------+
| 

STACK_MODEL_nnn  |           

nnn = SMALL or LARGE respectively according to the 
stack model used           |
+--------------------+--------------------------------------------------------------------------------------------+


In addition the following macros are defined when 
calling assembler:

+--------------------+--------------------------------------------------------------------------------------------+
|      

Macro       |                                       

Description                                        |
+--------------------+--------------------------------------------------------------------------------------------+
+--------------------+--------------------------------------------------------------------------------------------+
|    

__18Fxxxx     | 

MCU Identification. xxxx is the microcontrol 
identification number, i.e. 452, 6620, etc |
+--------------------+--------------------------------------------------------------------------------------------+
| 

SDCC_MODEL_nnn   |      

nnn = SMALL or LARGE respectively according to the 
memory model used for SDCC      |
+--------------------+--------------------------------------------------------------------------------------------+
| 

STACK_MODEL_nnn  |           

nnn = SMALL or LARGE respectively according to the 
stack model used           |
+--------------------+--------------------------------------------------------------------------------------------+


4.6.5 Directories

PIC16 port uses the following directories for searching 
header files and libraries.

+------------------------------+----------------------------+--------------+------------------+
|         

Directory          |       

Description        |   

Target   | 

Command prefix |
+------------------------------+----------------------------+--------------+------------------+
+------------------------------+----------------------------+--------------+------------------+
| 

PREFIX/sdcc/include/pic16  |  

PIC16 specific headers  |  

Compiler  |       

-I       |
+------------------------------+----------------------------+--------------+------------------+
|   

PREFIX/sdcc/lib/pic16    | 

PIC16 specific libraries |   

Linker   |       

-L       |
+------------------------------+----------------------------+--------------+------------------+


4.6.6 Pragmas<sub:PIC16_Pragmas>

The PIC16 port currently supports the following pragmas:

  stack This forces the code generator to initialize 
  the stack & frame pointers at a specific address. 
  This is an ad hoc solution for cases where no STACK 
  directive is available in the linker script or gplink 
  is not instructed to create a stack section.
The stack 
  pragma should be used only once in a project. 
  Multiple pragmas may result in indeterminate 
  behaviour of the program.

The old format (ie. #pragma stack 0x5ff) is deprecated 
and will cause the stack pointer to cross page 
boundaries (or even exceed the available data RAM) and 
crash the program. Make sure that stack does not cross 
page boundaries when using the SMALL stack model.

  The format is as follows:


#pragma stack bottom_address [stack_size]


bottom_address is the lower bound of the stack section. 
The stack pointer initially will point at address 
(bottom_address+stack_size-1).

Example:



/* initializes stack of 100 bytes at RAM address 0x200 */

#pragma stack 0x200 100

If the stack_size field is omitted then a stack is 
created with the default size of 64. This size might be 
enough for most programs, but its not enough for 
operations with deep function nesting or excessive 
stack usage.

  code Force a function to a static FLASH address.

Example:



/* place function test_func at 0x4000 */

#pragma code test_func 0x4000



  library instructs the linker to use a library module.
Usage:

#pragma library module_name

module_name can be any library or object file 
(including its path). Note that there are four reserved 
keywords which have special meaning. These are:

+------------+-------------------------------+------------------+
| 

Keyword  | 

Description                 | 

Module to link |
+------------+-------------------------------+------------------+
+------------+-------------------------------+------------------+
| 

ignore   | 

ignore all library pragmas  | 

(none)         |
+------------+-------------------------------+------------------+
|    

c     | 

link the C library          | 

libc18f.lib    |
+------------+-------------------------------+------------------+
|  

math    | 

link the Math libarary      | 

libm18f.lib    |
+------------+-------------------------------+------------------+
|   

io     | 

link the I/O library        | 

libio18f*.lib  |
+------------+-------------------------------+------------------+
|  

debug   | 

link the debug library      | 

libdebug.lib   |
+------------+-------------------------------+------------------+


* is the device number, i.e. 452 for PIC18F452 MCU.

This feature allows for linking with specific libraries 
withoug having to explicit name them in the command 
line. Note that the ignore keyword will reject all 
modules specified by the library pragma.

  udata The pragma udata instructs the compiler to emit 
  code so that linker will place a variable at a 
  specific memory bank.

Example:



/* places variable foo at bank2 */

#pragma udata bank2 foo

char foo;

In order for this pragma to work extra SECTION 
directives should be added in the .lkr script. In the 
following example a sample .lkr file is shown:



// Sample linker script for the PIC18F452 processor

LIBPATH .

CODEPAGE   NAME=vectors    START=0x0            
END=0x29           PROTECTED

CODEPAGE   NAME=page       START=0x2A           END=0x7FFF

CODEPAGE   NAME=idlocs     START=0x200000       
END=0x200007       PROTECTED

CODEPAGE   NAME=config     START=0x300000       
END=0x30000D       PROTECTED

CODEPAGE   NAME=devid      START=0x3FFFFE       
END=0x3FFFFF       PROTECTED

CODEPAGE   NAME=eedata     START=0xF00000       
END=0xF000FF       PROTECTED

ACCESSBANK NAME=accessram  START=0x0            END=0x7F



DATABANK   NAME=gpr0       START=0x80           END=0xFF

DATABANK   NAME=gpr1       START=0x100          END=0x1FF

DATABANK   NAME=gpr2       START=0x200          END=0x2FF

DATABANK   NAME=gpr3       START=0x300          END=0x3FF

DATABANK   NAME=gpr4       START=0x400          END=0x4FF

DATABANK   NAME=gpr5       START=0x500          END=0x5FF

ACCESSBANK NAME=accesssfr  START=0xF80          
END=0xFFF          PROTECTED



SECTION    NAME=CONFIG     ROM=config



SECTION    NAME=bank0      RAM=gpr0       # these 
SECTION directives

SECTION    NAME=bank1      RAM=gpr1       # should be 
added to link

SECTION    NAME=bank2      RAM=gpr2       # section 
name 'bank?' with

SECTION    NAME=bank3      RAM=gpr3       # a specific 
DATABANK name

SECTION    NAME=bank4      RAM=gpr4

SECTION    NAME=bank5      RAM=gpr5

The linker will recognise the section name set in the 
pragma statement and will position the variable at the 
memory bank set with the RAM field at the SECTION line 
in the linker script file.

4.6.7 Header Files<sub:PIC16_Header-Files>

There is one main header file that can be included to 
the source files using the pic16 port. That file is the 
pic18fregs.h. This header file contains the definitions 
for the processor special registers, so it is necessary 
if the source accesses them. It can be included by 
adding the following line in the beginning of the file:

#include <pic18fregs.h>

The specific microcontroller is selected within the 
pic18fregs.h automatically, so the same source can be 
used with a variety of devices.

4.6.8 Libraries

The libraries that PIC16 port depends on are the 
microcontroller device libraries which contain the 
symbol definitions for the microcontroller special 
function registers. These libraries have the format 
pic18fxxxx.lib, where xxxx is the microcontroller 
identification number. The specific library is selected 
automatically by the compiler at link stage according 
to the selected device.

Libraries are created with gplib which is part of the 
gputils package [http://sourceforge.net/projects/gputils].

 Building the libraries

Before using SDCC/pic16 there are some libraries that 
need to be compiled. This process is not done 
automatically by SDCC since not all users use SDCC for 
pic16 projects. So each user should compile the 
libraries separately.

The steps to compile the pic16 libraries under Linux 
and Mac OS X are:

cd device/lib/pic16

./configure

make

cd ..

make model-pic16

su -c 'make install'     # install the libraries, you 
need the root password

If you need to install the headers too, do:

cd device/include

su -c 'make install'     # install the headers, you 
need the root password

There exist a special target to build the I/O 
libraries. This target is not automatically build 
because it will build the I/O library for every 
supported device. This way building will take quite a 
lot of time. Users are advised to edit the 
device/lib/pic16/pics.build file and then execute:

make lib-io

4.6.9 Adding New Devices to the Port

Adding support for a new 16bit PIC MCU requires the 
following steps:

1. Create picDEVICE.c and picDEVICE.h from pDEVICE.inc using

  perl /path/to/sdcc/support/scripts/inc2h-pic16.pl 
  /path/to/gputils/header/pDEVICE.inc

2. mv picDEVICE.h /path/to/sdcc/device/include/pic16

3. mv picDEVICE.c /path/to/sdcc/device/lib/pic16/libdev

4. Add DEVICE to 
  /path/to/sdcc/device/lib/pic16/pics.all (and .build).

  Note: No 18f prefix here!

5. Adjust /path/to/sdcc/device/lib/pic16/libio/*.ignore

  Add your DEVICE if it does not compile in adc, i2c, 
  or usart.

6. Edit 
  /path/to/sdcc/device/include/pic16/pic18fregs.h. The 
  file format is self-explanatory, just add
#elif 
  defined(picDEVICE)
# include <picDEVICE.h>
at the right 
  place (keep it sorted).

7. Edit /path/to/sdcc/src/pic16/devices.inc. Copy and 
  modify an existing entry and insert it at the correct 
  place (keep the file sorted). The file is hardly 
  documented, look at the entries for the 18f2221...

8. Recompile SDCC, including the pic16 libraries.

4.6.10 Memory Models

The following memory models are supported by the PIC16 port:

* small model

* large model

Memory model affects the default size of pointers 
within the source. The sizes are shown in the next table:

+-------------------------------------------++----------------+---------------+
| 

Pointer sizes according to memory model || 

small model  | 

large model |
+-------------------------------------------++----------------+---------------+
+-------------------------------------------++----------------+---------------+
|              

code pointers              ||   

16-bits    |   

24-bits   |
+-------------------------------------------+                 +---------------+
+-------------------------------------------++----------------+---------------+
|              

data pointers              ||   

16-bits    |   

16-bits   |
+-------------------------------------------++----------------+---------------+


It is advisable that all sources within a project are 
compiled with the same memory model. If one wants to 
override the default memory model, this can be done by 
declaring a pointer as far or near. Far selects large 
memory model's pointers, while near selects small 
memory model's pointers.

The standard device libraries (see [sub:PIC16_Header-Files]) contain no 
reference to pointers, so they can be used with both 
memory models.

4.6.11 Stack

The stack implementation for the PIC16 port uses two 
indirect registers, FSR1 and FSR2.

  FSR1 is assigned as stack pointer

  FSR2 is assigned as frame pointer

The following stack models are supported by the PIC16 port

* small model

* large model

Small model means that only the FSRxL byte is used to 
access stack and frame, while large uses both FSRxL and 
FSRxH registers. The following table shows the 
stack/frame pointers sizes according to stack model and 
the maximum space they can address:

+--------------------------------------------------------++-----------+-----------+
| 

Stack & Frame pointer sizes according to stack model || 

small   |  

large  |
+--------------------------------------------------------++-----------+-----------+
+--------------------------------------------------------++-----------+-----------+
|                  

Stack pointer FSR1                  || 

8-bits  | 

16-bits |
+--------------------------------------------------------++-----------+-----------+
|                  

Frame pointer FSR2                  || 

8-bits  | 

16-bits |
+--------------------------------------------------------++-----------+-----------+


Large stack model is currently not working properly 
throughout the code generator. So its use is not 
advised. Also there are some other points that need 
special care:


1. Do not create stack sections with size more than one 
  physical bank (that is 256 bytes)

2. Stack sections should no cross physical bank limits 
  (i.e. #pragma stack 0x50 0x100)

These limitations are caused by the fact that only 
FSRxL is modified when using SMALL stack model, so no 
more than 256 bytes of stack can be used. This problem 
will disappear after LARGE model is fully implemented.

4.6.12 Functions

In addition to the standard SDCC function keywords, PIC16
 port makes available two more:

  wparam Use the WREG to pass one byte of the first 
  function argument. This improves speed but you may 
  not use this for functions with arguments that are 
  called via function pointers, otherwise the first 
  byte of the first parameter will get lost. Usage:

void func_wparam(int a) wparam

{

    /* WREG hold the lower part of a */

    /* the high part of a is stored in FSR2+2 (or +3 
for large stack model) */

...

}

  shadowregs When entering/exiting an ISR, it is 
  possible to take advantage of the PIC18F hardware 
  shadow registers which hold the values of WREG, 
  STATUS and BSR registers. This can be done by adding 
  the keyword shadowregs before the interrupt keyword 
  in the function's header.

void isr_shadow(void) shadowregs interrupt 1

{

...

}

shadowregs instructs the code generator not to 
store/restore WREG, STATUS, BSR when entering/exiting 
the ISR.

4.6.13 Function return values

Return values from functions are placed to the 
appropriate registers following a modified Microchip 
policy optimized for SDCC. The following table shows 
these registers:

+-------------+------------------------------------------+
|   

size    |          

destination register          |
+-------------+------------------------------------------+
+-------------+------------------------------------------+
|  

8 bits   |                  

WREG                  |
+-------------+------------------------------------------+
| 

16 bits   |               

PRODL:WREG               |
+-------------+------------------------------------------+
| 

24 bits   |            

PRODH:PRODL:WREG            |
+-------------+------------------------------------------+
| 

32 bits   |         

FSR0L:PRODH:PRODL:WREG         |
+-------------+------------------------------------------+
| 

>32 bits  | 

on stack, FSR0 points to the beginning |
+-------------+------------------------------------------+


4.6.14 Interrupts

An interrupt service routine (ISR) is declared using 
the interrupt keyword.

void isr(void) interrupt n

{

...

}

n is the interrupt number, which for PIC18F devices can be:

+------+-----------------------------+----------------------------+
| 

n  |     

Interrupt Vector      | 

Interrupt Vector Address |
+------+-----------------------------+----------------------------+
+------+-----------------------------+----------------------------+
| 

0  |       

RESET vector        |         

0x000000         |
+------+-----------------------------+----------------------------+
| 

1  | 

HIGH priority interrupts  |         

0x000008         |
+------+-----------------------------+----------------------------+
| 

2  | 

LOW priority interrupts   |         

0x000018         |
+------+-----------------------------+----------------------------+


When generating assembly code for ISR the code 
generator places a goto instruction at the Interrupt 
Vector Address which points at the genetated ISR. This 
single GOTO instruction is part of an automatically 
generated interrupt entry point function. The actuall 
ISR code is placed as normally would in the code space. 
Upon interrupt request, the GOTO instruction is 
executed which jumps to the ISR code. When declaring 
interrupt functions as _naked this GOTO instruction is 
not generated. The whole interrupt functions is 
therefore placed at the Interrupt Vector Address of the 
specific interrupt. This is not a problem for the LOW 
priority interrupts, but it is a problem for the RESET 
and the HIGH priority interrupts because code may be 
written at the next interrupt's vector address and 
cause undeterminate program behaviour if that interrupt 
is raised.

This is not a problem when

1. this is a HIGH interrupt ISR and LOW interrupts are 
  disabled or not used.

2. when the ISR is small enough not to reach the next 
  interrupt's vector address.

n may be omitted. This way a function is generated 
similar to an ISR, but it is not assigned to any interrupt.

When entering an interrupt, currently the PIC16 port 
automatically saves the following registers:

* WREG

* STATUS

* BSR

* PROD (PRODL and PRODH)

* FSR0 (FSR0L and FSR0H)

These registers are restored upon return from the 
interrupt routine.

NOTE that when the _naked attribute is specified for an 
interrupt routine, then NO registers are stored or restored.

4.6.15 Generic Pointers

Generic pointers are implemented in PIC16 port as 
3-byte (24-bit) types. There are 3 types of generic 
pointers currently implemented data, code and eeprom 
pointers. They are differentiated by the value of the 
7th and 6th bits of the upper byte:

+-------------------+-------------+-----------+---------------------------------------------------------------------------+
|  

pointer type   |  

7th bit  | 

6th bit |    

rest of the pointer       

description                              |
+-------------------+-------------+-----------+---------------------------------------------------------------------------+
+-------------------+-------------+-----------+---------------------------------------------------------------------------+
|      

data       |     

1     |    

0    |  

uuuuuu uuuuxxxx xxxxxxxx    

a 12-bit data pointer in data RAM memory |
+-------------------+-------------+-----------+---------------------------------------------------------------------------+
|      

code       |     

0     |    

0    |  

uxxxxx xxxxxxxx xxxxxxxx    

a 21-bit code pointer in FLASH memory    |
+-------------------+-------------+-----------+---------------------------------------------------------------------------+
|     

eeprom      |     

0     |    

1    |  

uuuuuu uuuuuuxx xxxxxxxx    

a 10-bit eeprom pointer in EEPROM memory |
+-------------------+-------------+-----------+---------------------------------------------------------------------------+
| 

(unimplemented) |     

1     |    

1    |  

xxxxxx xxxxxxxx xxxxxxxx    

unimplemented pointer type               |
+-------------------+-------------+-----------+---------------------------------------------------------------------------+


Generic pointer are read and written with a set of 
library functions which read/write 1, 2, 3, 4 bytes.

4.6.16 PIC16 C Libraries

4.6.16.1 Standard I/O Streams

In the stdio.h the type FILE is defined as:

typedef char * FILE;

This type is the stream type implemented I/O in the 
PIC18F devices. Also the standard input and output 
streams are declared in stdio.h:

extern FILE * stdin;

extern FILE * stdout;

The FILE type is actually a generic pointer which 
defines one more type of generic pointers, the stream 
pointer. This new type has the format:

+----------------+-----------+--------+--------+---------+---------------------------------------------------------------------------------+
| 

pointer type |  

<7:6>  | 

<5>  | 

<4>  | 

<3:0> |  

rest of the pointer    

descrption                                          |
+----------------+-----------+--------+--------+---------+---------------------------------------------------------------------------------+
+----------------+-----------+--------+--------+---------+---------------------------------------------------------------------------------+
|    

stream    |   

00    |  

1   |  

0   | 

nnnn  |   

uuuuuuuu uuuuuuuu     

upper byte high nubble is 0x2n, the rest are zeroes |
+----------------+-----------+--------+--------+---------+---------------------------------------------------------------------------------+


Currently implemented there are 3 types of streams defined:

+-----------------+---------------+-----------+------------------------------------------------------+
| 

stream type   |   

value     | 

module  |                    

description                     |
+-----------------+---------------+-----------+------------------------------------------------------+
+-----------------+---------------+-----------+------------------------------------------------------+
| 

STREAM_USART  | 

0x200000UL  | 

USART   |  

Writes/Reads characters via the USART peripheral  |
+-----------------+---------------+-----------+------------------------------------------------------+
| 

STREAM_MSSP   | 

0x210000UL  |  

MSSP   |  

Writes/Reads characters via the MSSP peripheral   |
+-----------------+---------------+-----------+------------------------------------------------------+
| 

STREAM_USER   | 

0x2f0000UL  | 

(none)  | 

Writes/Reads characters via used defined functions |
+-----------------+---------------+-----------+------------------------------------------------------+


The stream identifiers are declared as macros in the 
stdio.h header.

In the libc library there exist the functions that are 
used to write to each of the above streams. These are

  __stream_usart_putchar writes a character at the 
  USART stream

  __stream_mssp_putchar writes a character at the MSSP stream

  putchar dummy function. This writes a character to a 
  user specified manner.

In order to increase performance putchar is declared in 
stdio.h as having its parameter in WREG (it has the 
wparam keyword). In stdio.h exists the macro 
PUTCHAR(arg) that defines the putchar function in a 
user-friendly way. arg is the name of the variable that 
holds the character to print. An example follows:

#include <pic18fregs.h>
#include <stdio.h>

PUTCHAR( c )

{

    PORTA = c;    /* dump character c to PORTA */

} 

void main(void)

{

    stdout = STREAM_USER;    /* this is not necessary, 
since stdout points

                              * by default to 
STREAM_USER */

    printf ("This is a printf test\n");

}



4.6.16.2 Printing functions

PIC16 contains an implementation of the printf-family 
of functions. There exist the following functions:

extern unsigned int sprintf(char *buf, char *fmt, ...);

extern unsigned int vsprintf(char *buf, char *fmt, 
va_list ap);



extern unsigned int printf(char *fmt, ...);

extern unsigned int vprintf(char *fmt, va_lista ap);



extern unsigned int fprintf(FILE *fp, char *fmt, ...);

extern unsigned int vfprintf(FILE *fp, char *fmt, 
va_list ap);

For sprintf and vsprintf buf should normally be a data 
pointer where the resulting string will be placed. No 
range checking is done so the user should allocate the 
necessery buffer. For fprintf and vfprintf fp should be 
a stream pointer (i.e. stdout, STREAM_MSSP, etc...).

4.6.16.3 Signals

The PIC18F family of microcontrollers supports a number 
of interrupt sources. A list of these interrupts is 
shown in the following table:

+----------------+------------------------------++----------------+-----------------------------------------+
| 

signal name  |        

description         || 

signal name  |              

descritpion              |
+----------------+------------------------------++----------------+-----------------------------------------+
+----------------+------------------------------++----------------+-----------------------------------------+
| 

SIG_RB       |   

PORTB change interrupt   || 

SIG_EE       | 

EEPROM/FLASH write complete interrupt |
+----------------+------------------------------++----------------+-----------------------------------------+
| 

SIG_INT0     |  

INT0 external interrupt   || 

SIG_BCOL     |        

Bus collision interrupt        |
+----------------+------------------------------++----------------+-----------------------------------------+
| 

SIG_INT1     |  

INT1 external interrupt   || 

SIG_LVD      |     

Low voltage detect interrupt      |
+----------------+------------------------------++----------------+-----------------------------------------+
| 

SIG_INT2     |  

INT2 external interrupt   || 

SIG_PSP      |     

Parallel slave port interrupt     |
+----------------+------------------------------++----------------+-----------------------------------------+
| 

SIG_CCP1     |   

CCP1 module interrupt    || 

SIG_AD       |   

AD convertion complete interrupt    |
+----------------+------------------------------++----------------+-----------------------------------------+
| 

SIG_CCP2     |   

CCP2 module interrupt    || 

SIG_RC       |        

USART receive interrupt        |
+----------------+------------------------------++----------------+-----------------------------------------+
| 

SIG_TMR0     |  

TMR0 overflow interrupt   || 

SIG_TX       |       

USART transmit interrupt        |
+----------------+------------------------------++----------------+-----------------------------------------+
| 

SIG_TMR1     |  

TMR1 overflow interrupt   || 

SIG_MSSP     |    

SSP receive/transmit interrupt     |
+----------------+------------------------------++----------------+-----------------------------------------+
| 

SIG_TMR2     | 

TMR2 matches PR2 interrupt || 

             |                   

                    |
+----------------+------------------------------++----------------+-----------------------------------------+
| 

SIG_TMR3     |  

TMR3 overflow interrupt   || 

             |                   

                    |
+----------------+------------------------------++----------------+-----------------------------------------+


The prototypes for these names are defined in the 
header file signal.h .

In order to simplify signal handling, a number of 
macros is provided:

DEF_INTHIGH(name) begin the definition of the interrupt 
dispatch table for high priority interrupts. name is 
the function name to use.

DEF_INTLOW(name) begin the definition of the interrupt 
dispatch table fo low priority interrupt. name is the 
function name to use.

DEF_HANDLER(sig,handler) define a handler for signal sig.

END_DEF end the declaration of the dispatch table.

Additionally there are two more macros to simplify the 
declaration of the signal handler:

SIGHANDLER(handler) this declares the function 
prototype for the handler function.

SIGHANDLERNAKED(handler) same as SIGHANDLER() but 
declares a naked function.

An example of using the macros above is shown below:

#include <pic18fregs.h>

#include <signal.h>

DEF_INTHIGH(high_int)

DEF_HANDLER(SIG_TMR0, _tmr0_handler)

DEF_HANDLER(SIG_BCOL, _bcol_handler)

END_DEF

SIGHANDLER(_tmr0_handler)

{

  /* action to be taken when timer 0 overflows */

}

SIGHANDLERNAKED(_bcol_handler)

{

  _asm

    /* action to be taken when bus collision occurs */

    retfie

 _endasm;

}

NOTES: Special care should be taken when using the 
above scheme:

* do not place a colon (;) at the end of the DEF_* and 
  END_DEF macros.

* when declaring SIGHANDLERNAKED handler never forget 
  to use retfie for proper returning.

4.6.17 PIC16 Port -- Tips

Here you can find some general tips for compiling 
programs with SDCC/pic16.

4.6.17.1 Stack size

The default stack size (that is 64 bytes) probably is 
enough for many programs. One must take care that when 
there are many levels of function nesting, or there is 
excessive usage of stack, its size should be extended. 
An example of such a case is the printf/sprintf family 
of functions. If you encounter problems like not being 
able to print integers, then you need to set the stack 
size around the maximum (256 for small stack model). 
The following diagram shows what happens when calling 
printf to print an integer:

printf () --> ltoa () --> ultoa () --> divschar ()

It is should be understood that stack is easily 
consumed when calling complicated functions. Using 
command line arguments like --fommit-frame-pointer 
might reduce stack usage by not creating unnecessery 
stack frames. Other ways to reduce stack usage may exist.

4.6.18 Known Bugs

The PIC16 Port currently does not pass SDCC's 
regression test suite (see section [sec:Quality-control]) and thus the 
snapshot build regression tests for the PIC16 target 
are currently disabled for all hosts.

Debugging

There are several approaches to debugging your code. 
This chapter is meant to show your options and to give 
detail on some of them:

When writing your code:

* write your code with debugging in mind (avoid 
  duplicating code, put conceptually similar variables 
  into structs, use structured code, have strategic 
  points within your code where all variables are 
  consistent, ...)

* run a syntax-checking tool like splint (see -
  -more-pedantic [lyx:more-pedantic-SPLINT]) over the code.

* for the high level code use a C-compiler (like f.e. 
  GCC) to compile run and debug the code on your host. 
  See (see --more-pedantic [lyx:more-pedantic-SPLINT]) on how to handle syntax 
  extensions like __xdata, __at(), ... 

* use another C-compiler to compile code for your 
  target. Always an option but not recommended:) And 
  not very likely to help you. If you seriously 
  consider walking this path you should at least 
  occasionally check portability of your code. Most 
  commercial compiler vendors will offer an evaluation 
  version so you can test compile your code or snippets 
  of your code.

Debugging on a simulator:

* there is a separate section about SDCDB (section [cha:Debugging-with-SDCDB]) below.

* or (8051 specific) use a freeware/commercial 
  simulator which interfaces to the AOMF file (see [OMF file]) 
  optionally generated by SDCC.

Debugging On-target: 

* use a MCU port pin to serially output debug data to 
  the RS232 port of your host. You'll probably want 
  some level shifting device typically involving a 
  MAX232 or similar IC. If the hardware serial port of 
  the MCU is not available search for 'Software UART' 
  in your favourite search machine.

* use an on-target monitor. In this context a monitor 
  is a small program which usually accepts commands via 
  a serial line and allows to set program counter, to 
  single step through a program and read/write memory 
  locations. For the 8051 good examples of monitors are 
  paulmon and cmon51 (see section [sec:Related-open-source-tools]).

* toggle MCU port pins at strategic points within your 
  code and use an oscilloscope. A digital oscilloscope 
  with deep trace memory is really helpful especially 
  if you have to debug a realtime application. If you 
  need to monitor more pins than your oscilloscope 
  provides you can sometimes get away with a small R-2R 
  network. On a single channel oscilloscope you could 
  f.e. monitor 2 push-pull driven pins by connecting 
  one via a 10 k\Omega  resistor and the other one by a 5 k\Omega  
  resistor to the oscilloscope probe (check output 
  drive capability of the pins you want to monitor). If 
  you need to monitor many more pins a logic analyzer 
  will be handy.

* use an ICE (in circuit emulator). Usually very 
  expensive. And very nice to have too. And usually 
  locks you (for years...) to the devices the ICE can 
  emulate. 

* use a remote debugger. In most 8-bit systems the 
  symbol information is not available on the target, 
  and a complete debugger is too bulky for the target 
  system. Therefore usually a debugger on the host 
  system connects to an on-target debugging stub which 
  accepts only primitive commands. 
Terms to enter into 
  your favourite search engine could be 'remote 
  debugging', 'gdb stub' or 'inferior debugger'. (is 
  there one?)

* use an on target hardware debugger. Some of the more 
  modern MCUs include hardware support for setting 
  break points and monitoring/changing variables by 
  using dedicated hardware pins. This facility doesn't 
  require additional code to run on the target and 
  usually doesn't affect runtime behaviour until a 
  breakpoint is hit. For the mcs51 most hardware 
  debuggers use the AOMF file (see [OMF file]) as input file. 

Last not least:

* if you are not familiar with any of the following 
  terms you're likely to run into problems rather 
  sooner than later: volatile, atomic, memory map, 
  overlay. As an embedded programmer you have to know 
  them so why not look them up before you have problems?)

* tell someone else about your problem (actually this 
  is a surprisingly effective means to hunt down the 
  bug even if the listener is not familiar with your 
  environment). As 'failure to communicate' is probably 
  one of the job-induced deformations of an embedded 
  programmer this is highly encouraged.

5.1 Debugging with SDCDB<cha:Debugging-with-SDCDB> 

SDCC is distributed with a source level debugger. The 
debugger uses a command line interface, the command 
repertoire of the debugger has been kept as close to gdb
 (the GNU debugger) as possible. The configuration and 
build process is part of the standard compiler 
installation, which also builds and installs the 
debugger in the target directory specified during 
configuration. The debugger allows you debug BOTH at 
the C source and at the ASM source level.

5.1.1 Compiling for Debugging

The --debug option must be specified for all files for 
which debug information is to be generated. The 
compiler generates a .adb file for each of these files. 
The linker creates the .cdb file from the .adb files 
and the address information. This .cdb is used by the debugger.

5.1.2 How the Debugger Works

When the --debug option is specified the compiler 
generates extra symbol information some of which are 
put into the assembler source and some are put into the 
.adb file. Then the linker creates the .cdb file from 
the individual .adb files with the address information 
for the symbols. The debugger reads the symbolic 
information generated by the compiler & the address 
information generated by the linker. It uses the 
SIMULATOR (Daniel's S51) to execute the program, the 
program execution is controlled by the debugger. When a 
command is issued for the debugger, it translates it 
into appropriate commands for the simulator. (Currently 
SDCDM only connects to the simulator but newcdb at [http://ec2drv.sf.net/] is 
an effort to connect directly to the hardware.) 

5.1.3 Starting the Debugger SDCDB

The debugger can be started using the following command 
line. (Assume the file you are debugging has the file 
name foo).

sdcdb foo

The debugger will look for the 
following files.

* foo.c - the source file.

* foo.cdb - the debugger symbol information file.

* foo.ihx - the Intel hex format object file.

5.1.4 SDCDB Command Line Options

* --directory=<source file directory> this option can 
  used to specify the directory search list. The 
  debugger will look into the directory list specified 
  for source, cdb & ihx files. The items in the 
  directory list must be separated by ':', e.g. if the 
  source files can be in the directories /home/src1 and 
  /home/src2, the --directory option should be -
  -directory=/home/src1:/home/src2. Note there can be 
  no spaces in the option. 

* -cd <directory> - change to the <directory>.

* -fullname - used by GUI front ends.

* -cpu <cpu-type> - this argument is passed to the 
  simulator please see the simulator docs for details.

* -X <Clock frequency > this options is passed to the 
  simulator please see the simulator docs for details.

* -s <serial port file> passed to simulator see the 
  simulator docs for details.

* -S <serial in,out> passed to simulator see the 
  simulator docs for details.

* -k <port number> passed to simulator see the 
  simulator docs for details.

5.1.5 SDCDB Debugger Commands

As mentioned earlier the command interface for the 
debugger has been deliberately kept as close the GNU 
debugger gdb, as possible. This will help the 
integration with existing graphical user interfaces 
(like ddd, xxgdb or xemacs) existing for the GNU 
debugger. If you use a graphical user interface for the 
debugger you can skip this section.

 break [line | file:line | function | file:function]

Set breakpoint at specified line or function:


sdcdb>break 100 
sdcdb>break foo.c:100
sdcdb>break funcfoo

sdcdb>break foo.c:funcfoo

 clear [line | file:line | function | file:function ]

Clear breakpoint at specified line or function:


sdcdb>clear 100
sdcdb>clear foo.c:100
sdcdb>clear funcfoo

sdcdb>clear foo.c:funcfoo

 continue

Continue program being debugged, after breakpoint.

 finish

Execute till the end of the current function.

 delete [n]

Delete breakpoint number 'n'. If used without any 
option clear ALL user defined break points.

 info [break | stack | frame | registers ]

* info break - list all breakpoints

* info stack - show the function call stack.

* info frame - show information about the current 
  execution frame.

* info registers - show content of all registers.

 step

Step program until it reaches a different source line. 
Note: pressing <return> repeats the last command.

 next

Step program, proceeding through subroutine calls.

 run

Start debugged program.

 ptype variable 

Print type information of the variable.

 print variable

print value of variable.

 file filename

load the given file name. Note this is an alternate 
method of loading file for debugging.

 frame

print information about current frame.

 set srcmode

Toggle between C source & assembly source.

 ! simulator command

Send the string following '!' to the simulator, the 
simulator response is displayed. Note the debugger does 
not interpret the command being sent to the simulator, 
so if a command like 'go' is sent the debugger can 
loose its execution context and may display incorrect values.

 quit

"Watch me now. Iam going Down. My name is Bobby Brown"

5.1.6 Interfacing SDCDB with DDD



The portable network graphics File [http://sdcc.svn.sourceforge.net/viewvc/*checkout*/sdcc/trunk/sdcc/doc/figures/ddd_example.png] shows a screenshot 
of a debugging session with DDD (Unix only) on a 
simulated 8032. The debugging session might not run as 
smoothly as the screenshot suggests. The debugger 
allows setting of breakpoints, displaying and changing 
variables, single stepping through C and assembler 
code. 
The source was compiled with 

sdcc --debug 
ddd_example.c 

and DDD was invoked with 

ddd -debugger 
"sdcdb -cpu 8032 ddd_example"



5.1.7 Interfacing SDCDB with XEmacs

Two files (in emacs lisp) are provided for the 
interfacing with XEmacs, sdcdb.el and sdcdbsrc.el. 
These two files can be found in the $(prefix)/bin 
directory after the installation is complete. These 
files need to be loaded into XEmacs for the interface 
to work. This can be done at XEmacs startup time by 
inserting the following into your '.xemacs' file (which 
can be found in your HOME directory): 

(load-file 
sdcdbsrc.el) 

.xemacs is a lisp file so the () around 
the command is REQUIRED. The files can also be loaded 
dynamically while XEmacs is running, set the 
environment variable 'EMACSLOADPATH' to the 
installation bin directory (<installdir>/bin), then 
enter the following command ESC-x load-file sdcdbsrc. 
To start the interface enter the following command: 


ESC-x sdcdbsrc

You will prompted to enter the file name 
to be debugged. 

The command line options that are 
passed to the simulator directly are bound to default 
values in the file sdcdbsrc.el. The variables are 
listed below, these values maybe changed as required.

* sdcdbsrc-cpu-type '51

* sdcdbsrc-frequency '11059200

* sdcdbsrc-serial nil

The following is a list of key mapping for the debugger 
interface.

 
;; Current Listing :: 
;;key              binding                      Comment 
;;---              -------                      -------

;; 
;; n               sdcdb-next-from-src          SDCDB next command 
;; b               
sdcdb-back-from-src          SDCDB back command 
;; c               sdcdb-cont-from-src          
SDCDB continue command
;; s               sdcdb-step-from-src          SDCDB step 
command 
;; ?               sdcdb-whatis-c-sexp          SDCDB ptypecommand for 
data at 
;;                                               buffer point 
;; x               sdcdbsrc-delete              SDCDB Delete 
all breakpoints if no arg 
;;                                               given or delete arg (C-u 
arg x) 
;; m               sdcdbsrc-frame               SDCDB Display current frame if 
no arg, 
;;                                               given or display frame arg 
;;                                               buffer point 
;; !               
sdcdbsrc-goto-sdcdb          Goto the SDCDB output buffer 
;; p               
sdcdb-print-c-sexp           SDCDB print command for data at 
;;                                               
buffer point 
;; g               sdcdbsrc-goto-sdcdb          Goto the SDCDB 
output buffer 
;; t               sdcdbsrc-mode                Toggles Sdcdbsrc mode 
(turns it off) 
;; 
;; C-c C-f         sdcdb-finish-from-src        SDCDB 
finish command 
;; 
;; C-x SPC         sdcdb-break                  Set break for line 
with point 
;; ESC t           sdcdbsrc-mode                Toggle Sdcdbsrc mode 
;; ESC m           
sdcdbsrc-srcmode             Toggle list mode 
;; 



TIPS

Here are a few guidelines that will help the compiler 
generate more efficient code, some of the tips are 
specific to this compiler others are generally good 
programming practice.

* Use the smallest data type to represent your 
  data-value. If it is known in advance that the value 
  is going to be less than 256 then use an 'unsigned 
  char' instead of a 'short' or 'int'. Please note, 
  that ANSI C requires both signed and unsigned chars 
  to be promoted to 'signed int'

 !
   before doing any operation. This promotion<type promotion> can be 
  omitted, if the result is the same. The effect of the 
  promotion rules together with the sign-extension is 
  often surprising:

  unsigned char uc = 0xfe;
if (uc * uc < 0) /* this is 
  true! */
{
    ....
}

  uc * uc is evaluated as (int) uc * (int) uc = (int) 
  0xfe * (int) 0xfe = (int) 0xfc04 = -1024. 
Another one:

  (unsigned char) -12 / (signed char) -3 = ...

  No, the result is not 4:

  (int) (unsigned char) -12 / (int) (signed char) -3 =

  (int) (unsigned char) 0xf4 / (int) (signed char) 0xfd =

  (int) 0x00f4 / (int) 0xfffd =
(int) 0x00f4 / (int) 
  0xfffd =
(int) 244 / (int) -3 =
(int) -81 = (int) 0xffaf;

  Don't complain, that gcc gives you a different 
  result. gcc uses 32 bit ints, while SDCC uses 16 bit 
  ints. Therefore the results are different.
From "
  comp.lang.c FAQ":

  If well-defined overflow characteristics are 
  important and negative values are not, or if you want 
  to steer clear of sign-extension problems when 
  manipulating bits or bytes, use one of the 
  corresponding unsigned types. (Beware when mixing 
  signed and unsigned values in expressions, though.)

  Although character types (especially unsigned char) 
  can be used as "tiny" integers, doing so is sometimes 
  more trouble than it's worth, due to unpredictable 
  sign extension and increased code size.

* Use unsigned when it is known in advance that the 
  value is not going to be negative. This helps 
  especially if you are doing division or 
  multiplication, bit-shifting or are using an array index.

* NEVER jump into a LOOP.

* Declare the variables to be local whenever possible, 
  especially loop control variables (induction).

* Have a look at the assembly listing to get a "feeling" 
  for the code generation.

6.1 Porting code from or to other compilers<sec:Porting-code-to-other-compilers>

* check whether endianness of the compilers differs and 
  adapt where needed.

* check the device specific header files for compiler 
  specific syntax. Eventually include the file <compiler.h
  > [http://sdcc.svn.sourceforge.net/viewvc/sdcc/trunk/sdcc/device/include/mcs51/compiler.h?view=markup] to allow using common header files. (see f.e. 
  cc2510fx.h [http://sdcc.svn.sourceforge.net/viewvc/sdcc/trunk/sdcc/device/include/mcs51/cc2510fx.h?view=markup]).

* check whether the startup code contains the correct 
  initialization (watchdog, peripherals).

* check whether the sizes of short, int, long match.

* check if some 16 or 32 bit hardware registers require 
  a specific addressing order (least significant or 
  most significant byte first) and adapt if needed 
  (first and last relate to time and not to lower/upper 
  memory location here, so this is not the same as endianness).

* check whether the keyword volatile is used where 
  needed. The compilers might differ in their 
  optimization characteristics (as different versions 
  of the same compiler might also use more clever 
  optimizations this is good idea anyway). See section [sub:Common-interrupt-pitfall-volatile].

* check that the compilers are not told to supress warnings.

* check and convert compiler specific extensions 
  (interrupts, memory areas, pragmas etc.).

* check for differences in type promotion. Especially 
  check for math operations on char or unsigned char 
  variables. For the sake of C99 compatibility SDCC 
  will probably promote these to int more often than 
  other compilers. Eventually insert explicit casts to 
  (char) or (unsigned char). Also check that the ~ operator
   is not used on bit variables, use the ! operator 
  instead. See sections [type promotion] and [sec:Compatibility-with-previous].

* check the assembly code generated for interrupt 
  routines (f.e. for calls to possibly non-reentrant 
  library functions).

* check whether timing loops result in proper timing 
  (or preferably consider a rewrite of the code with 
  timer based delays instead).

* check for differences in printf parameters (some 
  compilers push (va_arg) char variables as int others 
  push them as char. See section [sec:Compatibility-with-previous]).

* check the resulting memory map. Usage of different 
  memory spaces: code, stack, data (for mcs51/ds390 
  additionally idata, pdata, xdata). Eventually check 
  if unexpected library functions are included.

6.2 Tools included in the distribution

+-----------------+----------------------------------------+------------------------+
| 

Name          | 

Purpose                              | 

Directory            |
+-----------------+----------------------------------------+------------------------+
+-----------------+----------------------------------------+------------------------+
| 

uCsim         | 

Simulator for various architectures  | 

sdcc/sim/ucsim       |
+-----------------+----------------------------------------+------------------------+
| 

keil2sdcc.pl  | 

header file conversion               | 

sdcc/support/scripts |
+-----------------+----------------------------------------+------------------------+
| 

mh2h.c        | 

header file conversion               | 

sdcc/support/scripts |
+-----------------+----------------------------------------+------------------------+
| 

as-gbz80      | 

Assembler                            | 

sdcc/bin             |
+-----------------+----------------------------------------+------------------------+
| 

as-z80        | 

Assembler                            | 

sdcc/bin             |
+-----------------+----------------------------------------+------------------------+
| 

asx8051       | 

Assembler                            | 

sdcc/bin             |
+-----------------+----------------------------------------+------------------------+
| 

SDCDB         | 

Simulator                            | 

sdcc/bin             |
+-----------------+----------------------------------------+------------------------+
| 

aslink        | 

Linker                               | 

sdcc/bin             |
+-----------------+----------------------------------------+------------------------+
| 

link-z80      | 

Linker                               | 

sdcc/bin             |
+-----------------+----------------------------------------+------------------------+
| 

link-gbz80    | 

Linker                               | 

sdcc/bin             |
+-----------------+----------------------------------------+------------------------+
| 

packihx       | 

Intel Hex packer                     | 

sdcc/bin             |
+-----------------+----------------------------------------+------------------------+



6.3 Documentation included in the distribution

+--------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------+
| 

Subject / Title                                      | 

Filename / Where to get                                                                                                                   |
+--------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------+
+--------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------+
| 

SDCC Compiler User Guide                             | 

You're reading it right now    	online at:
[http://sdcc.sourceforge.net/doc/sdccman.pdf]                                                  |
+--------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------+
| 

Changelog of SDCC                                    | 

sdcc/Changelog    	online at:
[http://sdcc.svn.sourceforge.net/viewvc/*checkout*/sdcc/trunk/sdcc/ChangeLog]                               |
+--------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------+
| 

ASXXXX Assemblers and
ASLINK Relocating Linker       | 

sdcc/as/doc/asxhtm.html    	online at:
[http://sdcc.svn.sourceforge.net/viewvc/*checkout*/sdcc/trunk/sdcc/as/doc/asxhtm.html]             |
+--------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------+
| 

SDCC regression test                                 | 

sdcc/doc/test_suite_spec.pdf    	online at:
[http://sdcc.sourceforge.net/doc/test_suite_spec.pdf]                                         |
+--------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------+
| 

Various notes                                        | 

sdcc/doc/*    	online at:
[http://sdcc.svn.sourceforge.net/viewvc/sdcc/trunk/sdcc/doc/]                                                   |
+--------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------+
| 

Notes on debugging with SDCDB                        | 

sdcc/debugger/README    	online at:
[http://sdcc.svn.sourceforge.net/viewvc/*checkout*/sdcc/trunk/sdcc/debugger/README]                   |
+--------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------+
| 

uCsim Software simulator for microcontrollers        | 

sdcc/sim/ucsim/doc/index.html    	online at:
[http://sdcc.svn.sourceforge.net/viewvc/*checkout*/sdcc/trunk/sdcc/sim/ucsim/doc/index.html] |
+--------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------+
| 

Temporary notes on the pic16 port                    | 

sdcc/src/pic16/NOTES    	online at:
[http://sdcc.svn.sourceforge.net/viewvc/*checkout*/sdcc/trunk/sdcc/src/pic16/NOTES]                   |
+--------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------+
| 

SDCC internal documentation (debugging file format)  | 

sdcc/doc/cdbfileformat.pdf    	online at:
[http://sdcc.sourceforge.net/doc/cdbfileformat.pdf]                                             |
+--------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------+



6.4 Related open source tools<sec:Related-open-source-tools>

+------------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------+
| 

Name           | 

Purpose                                                                                | 

Where to get                                                                                 |
+------------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------+
+------------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------+
| 

gpsim          | 

PIC simulator                                                                          | 

[http://www.dattalo.com/gnupic/gpsim.html]                                                   |
+------------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------+
| 

gputils        | 

GNU PIC utilities                                                                      | 

[http://sourceforge.net/projects/gputils]                                                    |
+------------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------+
| 

flP5           | 

PIC programmer                                                                         | 

[http://freshmeat.net/projects/flp5/]                                                        |
+------------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------+
| 

ec2drv/newcdb  | 

Tools for Silicon Laboratories JTAG debug adapter, 
partly based on SDCDB (Unix only)  | 

[http://sourceforge.net/projects/ec2drv]                                                     |
+------------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------+
| 

indent         | 

Formats C source - Master of the white spaces                                          | 

[http://directory.fsf.org/GNU/indent.html]                                                   |
+------------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------+
| 

srecord        | 

Object file conversion, checksumming, ...                                              | 

[http://sourceforge.net/projects/srecord]                                                    |
+------------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------+
| 

objdump        | 

Object file conversion, ...                                                            | 

Part of binutils (should be there anyway)                                                    |
+------------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------+
| 

cmon51         | 

8051 monitor (hex up-/download, single step, disassemble)                              | 

[http://sourceforge.net/projects/cmon51]                                                     |
+------------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------+
| 

doxygen        | 

Source code documentation system                                                       | 

[http://www.doxygen.org]                                                                     |
+------------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------+
| 

kdevelop       | 

IDE (has anyone tried integrating SDCC & SDCDB? Unix only)                             | 

[http://www.kdevelop.org]                                                                    |
+------------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------+
| 

paulmon        | 

8051 monitor (hex up-/download, single step, disassemble)                              | 

[http://www.pjrc.com/tech/8051/paulmon2.html]                                                |
+------------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------+
| 

splint         | 

Statically checks c sources (see [lyx:more-pedantic-SPLINT])                           | 

[http://www.splint.org]                                                                      |
+------------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------+
| 

ddd            | 

Debugger, serves nicely as GUI to SDCDB (Unix only)                                    | 

[http://www.gnu.org/software/ddd/]                                                           |
+------------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------+
| 

d52            | 

Disassembler, can count instruction cycles, use with 
options -pnd                     | 

[http://www.8052.com/users/disasm/]                                                          |
+------------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------+
| 

cmake          | 

Cross platform build system, generates Makefiles and 
project workspaces               | 

[http://www.cmake.org]     and a dedicated wiki entry: [http://www.cmake.org/Wiki/CmakeSdcc] |
+------------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------+



6.5 Related documentation / recommended reading

+----------------------+-----------------------------------+--------------------------------------------------------------------+
| 

Name               | 

Subject / Title                 | 

Where to get                                                     |
+----------------------+-----------------------------------+--------------------------------------------------------------------+
+----------------------+-----------------------------------+--------------------------------------------------------------------+
| 

c-refcard.pdf      | 

C Reference Card, 2 pages       | 

[http://refcards.com/refcards/c/index.html]                      |
+----------------------+-----------------------------------+--------------------------------------------------------------------+
| 

c-faq              | 

C-FAQ                           | 

[http://www.c-faq.com]                                           |
+----------------------+-----------------------------------+--------------------------------------------------------------------+
| 

ISO/IEC 9899:TC2   | 

"C-Standard"                    | 

[http://www.open-std.org/jtc1/sc22/wg14/www/standards.html#9899] |
+----------------------+-----------------------------------+--------------------------------------------------------------------+
| 

ISO/IEC DTR 18037  | 

"Extensions for Embedded C"     | 

[http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1021.pdf]      |
+----------------------+-----------------------------------+--------------------------------------------------------------------+
| 

                   | 

Latest datasheet of target CPU  | 

vendor                                                           |
+----------------------+-----------------------------------+--------------------------------------------------------------------+
| 

                   | 

Revision history of datasheet   | 

vendor                                                           |
+----------------------+-----------------------------------+--------------------------------------------------------------------+



6.6 Application notes specifically for SDCC

SDCC makes no claims about the completeness of this 
list and about up-to-dateness or correctness of the 
application notes.

+----------------------------------+----------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------+
| 

Vendor                         | 

Subject / Title                                                                                              | 

Where to get                                                                                   |
+----------------------------------+----------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------+
+----------------------------------+----------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------+
| 

Maxim / Dallas                 | 

Using the SDCC Compiler for the DS80C400                                                                     | 

[http://pdfserv.maxim-ic.com/en/an/AN3346.pdf]                                                 |
+----------------------------------+----------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------+
| 

Maxim / Dallas                 | 

Using the Free SDCC C Compiler to Develop Firmware for 
the DS89C420/430/440/450 Family of Microcontrollers  | 

[http://pdfserv.maxim-ic.com/en/an/AN3477.pdf]                                                 |
+----------------------------------+----------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------+
| 

Silicon Laboratories / Cygnal  | 

Integrating SDCC 8051 Tools Into The Silicon Labs IDE                                                        | 

[http://www.silabs.com/public/documents/tpub_doc/anote/Microcontrollers/en/an198.pdf]          |
+----------------------------------+----------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------+
| 

Ramtron / Goal Semiconductor   | 

Interfacing SDCC to Syn and Textpad                                                                          | 

[http://www.ramtron.com/doc/Products/Microcontroller/Support_Tools.asp]                        |
+----------------------------------+----------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------+
| 

Ramtron / Goal Semiconductor   | 

Installing and Configuring SDCC and Crimson Editor                                                           | 

[http://www.ramtron.com/doc/Products/Microcontroller/Support_Tools.asp]                        |
+----------------------------------+----------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------+
| 

Texas Instruments              | 

MSC12xx Programming with SDCC                                                                                | 

[http://focus.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=sbaa109&fileType=pdf] |
+----------------------------------+----------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------+


6.7 Some Questions

Some questions answered, some pointers given - it might 
be time to in turn ask you some questions: 

* can you solve your project with the selected 
  microcontroller? Would you find out early or rather 
  late that your target is too small/slow/whatever? Can 
  you switch to a slightly better device if it doesn't fit?

* should you solve the problem with an 8 bit CPU? Or 
  would a 16/32 bit CPU and/or another programming 
  language be more adequate? Would an operating system 
  on the target device help?

* if you solved the problem, will the marketing 
  department be happy?

* if the marketing department is happy, will customers 
  be happy?

* if you're the project manager, marketing department 
  and maybe even the customer in one person, have you 
  tried to see the project from the outside?

* is the project done if you think it is done? Or is 
  just that other 
  interface/protocol/feature/configuration/option 
  missing? How about website, manual(s), 
  internationali(z|s)ation, packaging, labels, 2nd 
  source for components, electromagnetic 
  compatability/interference, documentation for 
  production, production test software, update 
  mechanism, patent issues?

* is your project adequately positioned in that magic 
  triangle: fame, fortune, fun?

Maybe not all answers to these questions are known and 
some answers may even be no, nevertheless knowing these 
questions may help you to avoid burnout

burnout is bad for electronic devices, programmers and 
motorcycle tyres
. Chances are you didn't want to hear some of them...

Support

SDCC has grown to be a large project. The compiler 
alone (without the preprocessor, assembler and linker) 
is well over 150,000 lines of code (blank stripped). 
The open source nature of this project is a key to its 
continued growth and support. You gain the benefit and 
support of many active software developers and end 
users. Is SDCC perfect? No, that's why we need your 
help. The developers take pride in fixing reported 
bugs. You can help by reporting the bugs and helping 
other SDCC users. There are lots of ways to contribute, 
and we encourage you to take part in making SDCC a 
great software package. 

The SDCC project is hosted on the SDCC sourceforge site 
at [http://sourceforge.net/projects/sdcc]. You'll find the complete set of mailing lists, 
forums, bug reporting system, patch submission system, download
 area and Subversion code repository there.

7.1 Reporting Bugs

The recommended way of reporting bugs is using the 
infrastructure of the sourceforge site. You can follow 
the status of bug reports there and have an overview 
about the known bugs.

Bug reports are automatically forwarded to the 
developer mailing list and will be fixed ASAP. When 
reporting a bug, it is very useful to include a small 
test program (the smaller the better) which reproduces 
the problem. If you can isolate the problem by looking 
at the generated assembly code, this can be very 
helpful. Compiling your program with the --dumpall 
option can sometimes be useful in locating optimization 
problems. When reporting a bug please make sure you:

1. Attach the code you are compiling with SDCC. 

2. Specify the exact command you use to run SDCC, or 
  attach your Makefile. 

3. Specify the SDCC version (type "sdcc -v"), your 
  platform, and operating system. 

4. Provide an exact copy of any error message or 
  incorrect output. 

5. Put something meaningful in the subject of your message.

Please attempt to include these 5 important parts, as 
applicable, in all requests for support or when 
reporting any problems or bugs with SDCC. Though this 
will make your message lengthy, it will greatly improve 
your chance that SDCC users and developers will be able 
to help you. Some SDCC developers are frustrated by bug 
reports without code provided that they can use to 
reproduce and ultimately fix the problem, so please be 
sure to provide sample code if you are reporting a bug! 

Please have a short check that you are using a recent 
version of SDCC and the bug is not yet known. This is 
the link for reporting bugs: [http://sourceforge.net/tracker/?group_id=599&atid=100599]. With SDCC on average 
having more than 200 downloads on sourceforge per day

220 daily downloads on average Jan-Sept 2006 and about 
150 daily downloads between 2002 and 2005. This does 
not include other methods of distribution.
 there must be some users. So it's not exactly easy to 
find a new bug. If you find one we need it: reporting 
bugs is good.

7.2 Requesting Features<sub:Requesting-Features>

Like bug reports feature requests are forwarded to the 
developer mailing list. This is the link for requesting 
features: [http://sourceforge.net/tracker/?group_id=599&atid=350599].

7.3 Submitting patches

Like bug reports contributed patches are forwarded to 
the developer mailing list. This is the link for 
submitting patches: [http://sourceforge.net/tracker/?group_id=599&atid=300599].

You need to specify some parameters to the diff command 
for the patches to be useful. If you modified more than 
one file a patch created f.e. with "diff -Naur 
unmodified_directory modified_directory >my_changes.patch"
 will be fine, otherwise "diff -u sourcefile.c.orig 
sourcefile.c >my_changes.patch" will do.

7.4 Getting Help

These links should take you directly to the [http://sourceforge.net/mail/?group_id=599||Mailing lists]

Traffic on sdcc-devel and sdcc-user is about 100 
mails/month each not counting automated messages (mid 2003)
 and the [http://sourceforge.net/forum/?group_id=599||Forums], lists and forums are archived and searchable 
so if you are lucky someone already had a similar 
problem. While mails to the lists themselves are 
delivered promptly their web front end on sourceforge 
sometimes shows a severe time lag (up to several 
weeks), if you're seriously using SDCC please consider 
subscribing to the lists.

7.5 ChangeLog

You can follow the status of the Subversion version of 
SDCC by watching the Changelog in the Subversion 
repository [http://sdcc.svn.sourceforge.net/viewcvs.cgi/*checkout*/sdcc/trunk/sdcc/ChangeLog].

7.6 Subversion Source Code Repository

The output of sdcc --version or the filenames of the 
snapshot versions of SDCC include date and its Subversion
 number. Subversion allows to download the source of 
recent or previous versions [http://sourceforge.net/svn/?group_id=599] (by number or by date). An 
on-line source code browser and detailled instructions 
are also available there. SDCC versions starting from 
1999 up to now are available (currently the versions 
prior to the conversion from cvs to Subversion (April 
2006) are either by accessible by Subversion or by cvs).

7.7 Release policy

Historically there often were long delays between 
official releases and the sourceforge download area 
tends to get not updated at all. Excuses in the past 
might have referred to problems with live range 
analysis, but as this was fixed a while ago, the 
current problem is that another excuse has to be found. 
Kidding aside, we have to get better there! On the 
other hand there are daily snapshots available at [http://sdcc.sourceforge.net/snap.php||snap], and 
you can always build the very last version (hopefully 
with many bugs fixed, and features added) from the 
source code available at [http://sdcc.sourceforge.net/snap.php#Source||Source]. The SDCC Wiki at [http://sdcc.wiki.sourceforge.net/] also holds 
some information about past and future releases.

7.8 Examples

You'll find some small examples in the directory 
sdcc/device/examples/. More examples and libraries are 
available at The SDCC Open Knowledge Resource [http://sdccokr.dl9sec.de/] web site 
or at [http://www.pjrc.com/tech/8051/].



7.9 Quality control<sec:Quality-control>

The compiler is passed through snaphot build compile 
and build checks. The so called regression tests check 
that SDCC itself compiles flawlessly on several host 
platforms (i386, Opteron, 64 bit Alpha, ppc64, Mac OS X 
on ppc and i386, Solaris on Sparc) and checks the 
quality of the code generated by SDCC by running the 
code for several target platforms through simulators. 
The regression test suite comprises more than 100 files 
which expand to more than 500 test cases which include 
more than 4500 tests. The results of these tests are 
published daily on SDCC's snapshot page (click on the 
red or green symbols on the right side of [http://sdcc.sourceforge.net/snap.php]).

There is a separate document test_suite.pdf  [http://sdcc.sourceforge.net/doc/test_suite_spec.pdf] about the 
regression test suite.

You'll find the test code in the directory 
sdcc/support/regression. You can run these tests 
manually by running make in this directory (or f.e. "
make test-mcs51" if you don't want to run the complete 
tests). The test code might also be interesting if you 
want to look for examples checking corner cases of SDCC 
or if you plan to submit patches.

The PIC14 port uses a different set of regression tests 
, you'll find them in the directory sdcc/src/regression.

7.10 Use of SDCC in Education

In short: highly encouraged

the phrase "use in education" might evoke the 
association "only fit for use in education". This 
connotation is not intended but nevertheless risked as 
the licensing of SDCC makes it difficult to offer 
educational discounts
. If your rationales are to:

1. give students a chance to understand the complete 
  steps of code generation

2. have a curriculum that can be extended for years. 
  Then you could use an fpga board as target and your 
  curriculum will seamlessly extend from logic 
  synthesis ([opencores.org||http://www.opencores.org], [http://www.oregano.at/ip/ip01.htm||Oregano]), over assembly programming, to C to 
  FPGA compilers ([http://sf.net/projects/fpgac||FPGAC]) and to C.

3. be able to insert excursions about skills like using 
  a revision control system, submitting/applying 
  patches, using a type-setting (as opposed to 
  word-processing) engine LyX/LaTeX, using [http://www.sf.net||SourceForge], following 
  some [http://en.wikipedia.org/wiki/Netiquette||netiquette], understanding BSD/LGPL/GPL/Proprietary 
  licensing, growth models of Open Source Software, CPU 
  simulation, compiler regression tests. 
And if there 
  should be a shortage of ideas then you can always 
  point students to the ever-growing feature request 
  list [http://sourceforge.net/tracker/?group_id=599&atid=350599].

4. not tie students to a specific host platform and 
  instead allow them to use a host platform of their 
  choice (among them Alpha, i386, i386_64, Mac OS X, 
  Mips, Sparc, Windows and eventually [http://www.laptop.org||OLPC])

5. not encourage students to use illegal copies of 
  educational software

6. be immune to licensing/availability/price changes of 
  the chosen tool chain

7. be able to change to a new target platform without 
  having to adopt a new tool chain

8. have complete control over and insight into the tool chain

9. make your students aware about the pros and cons of 
  open source software development

10. give back to the public as you are probably at 
  least partially publically funded

11. give students a chance to publically prove their 
  skills and to possibly see a world wide impact

then SDCC is probably among the first choices. Well, 
probably SDCC might be the only choice.


SDCC Technical Data

8.1 Optimizations

SDCC performs a host of standard optimizations in 
addition to some MCU specific optimizations. 

8.1.1 Sub-expression Elimination

The compiler does local and global common subexpression 
elimination, e.g.: 

i = x + y + 1; 
j = x + y;

will be translated to

iTemp = x + y; 
i = iTemp + 1; 
j = iTemp;

Some subexpressions are not as obvious as the above 
example, e.g.:

a->b[i].c = 10; 
a->b[i].d = 11;

In this case the address arithmetic a->b[i] will be 
computed only once; the equivalent code in C would be.

iTemp = a->b[i]; 
iTemp.c = 10; 
iTemp.d = 11;

The compiler will try to keep these temporary variables 
in registers.

8.1.2 Dead-Code Elimination

int global;

void f () { 
  int i; 
  i = 1;      /* dead store */ 
  
global = 1; /* dead store */ 
  global = 2; 
  return; 
  global 
= 3; /* unreachable */ 
}

will be changed to

int global;

void f () {
  global = 2; 
}

8.1.3 Copy-Propagation

int f() { 
  int i, j; 
  i = 10; 
  j = i; 
  return j; 
}

will be changed to 

int f() { 
  int i, j; 
  i = 10; 
  j = 10; 
  return 10; 
}

Note: the dead stores created by this copy propagation 
will be eliminated by dead-code elimination.

8.1.4 Loop Optimizations<sub:Loop-Optimizations>

Two types of loop optimizations are done by SDCC loop 
invariant lifting and strength reduction of loop 
induction variables. In addition to the strength 
reduction the optimizer marks the induction variables 
and the register allocator tries to keep the induction 
variables in registers for the duration of the loop. 
Because of this preference of the register allocator, 
loop induction optimization causes an increase in 
register pressure, which may cause unwanted spilling of 
other temporary variables into the stack / data space. 
The compiler will generate a warning message when it is 
forced to allocate extra space either on the stack or 
data space. If this extra space allocation is 
undesirable then induction optimization can be 
eliminated either for the entire source file (with -
-noinduction option) or for a given function only using #pragma 
noinduction.

Loop Invariant:

for (i = 0 ; i < 100 ; i ++) 
    f += k + l;

changed to

itemp = k + l; 
for (i = 0; i < 100; i++) 
    f += itemp;

As mentioned previously some loop invariants are not as 
apparent, all static address computations are also 
moved out of the loop.

Strength Reduction, this 
optimization substitutes an expression by a cheaper expression:

for (i=0;i < 100; i++)
    ar[i*5] = i*3;

changed to

itemp1 = 0; 
itemp2 = 0; 
for (i=0;i< 100;i++) { 
    
ar[itemp1] = itemp2; 
    itemp1 += 5; 
    itemp2 += 3; 
}

The more expensive multiplication is changed to a less 
expensive addition.

8.1.5 Loop Reversing

This optimization is done to reduce the overhead of 
checking loop boundaries for every iteration. Some 
simple loops can be reversed and implemented using a "
decrement and jump if not zero" instruction. SDCC checks 
for the following criterion to determine if a loop is 
reversible (note: more sophisticated compilers use 
data-dependency analysis to make this determination, 
SDCC uses a more simple minded analysis).

* The 'for' loop is of the form 

for(<symbol> = 
  <expression>; <sym> [< | <=] <expression>; [<sym>++ | 
  <sym> += 1])
    <for body>

* The <for body> does not contain "continue" or 'break".

* All goto's are contained within the loop.

* No function calls within the loop.

* The loop control variable <sym> is not assigned any 
  value within the loop

* The loop control variable does NOT participate in any 
  arithmetic operation within the loop.

* There are NO switch statements in the loop.

8.1.6 Algebraic Simplifications

SDCC does numerous algebraic simplifications, the 
following is a small sub-set of these optimizations.

i = j + 0;     /* changed to: */     i = j; 
i /= 2;        /* changed 
to: */     i >>= 1; 
i = j - j;     /* changed to: */     i = 0; 
i = 
j / 1;     /* changed to: */     i = j;

Note the subexpressions given above are generally 
introduced by macro expansions or as a result of 
copy/constant propagation.

8.1.7 'switch' Statements<sub:'switch'-Statements>

SDCC can optimize switch statements to jump tables. It 
makes the decision based on an estimate of the 
generated code size. SDCC is quite liberal in the 
requirements for jump table generation: 

* The labels need not be in order, and the starting 
  number need not be one or zero, the case labels are 
  in numerical sequence or not too many case labels are missing.

  switch(i) {                          switch (i) { 
   case 4: ...                          case 0: ... 
   case 
  5: ...                          case 1: ... 
   case 3: ...                          
   case 6: ...                          case 3: ... 
   
  case 7: ...                          case 4: ... 
   case 8: ...                          case 5: ... 
   case 9: ...                          
  case 6: ... 
   case 10: ...                         case 7: ... 
   case 11: ...                         case 
  8: ... 
}                                    }

  Both the above switch statements will be implemented 
  using a jump-table. The example to the right side is 
  slightly more efficient as the check for the lower 
  boundary of the jump-table is not needed.

* The number of case labels is not larger than 
  supported by the target architecture.

* If the case labels are not in numerical sequence 
  ('gaps' between cases) SDCC checks whether a jump 
  table with additionally inserted dummy cases is still 
  attractive. 

* If the starting number is not zero and a check for 
  the lower boundary of the jump-table can thus be 
  eliminated SDCC might insert dummy cases 0, ... .

Switch statements which have large gaps in the numeric 
sequence or those that have too many case labels can be 
split into more than one switch statement for efficient 
code generation, e.g.:

switch (i) { 
  case 1: ... 
  case 2: ... 
  case 3: ... 
  case 
4: ... 
  case 5: ... 
  case 6: ... 
  case 7: ... 
  case 101: 
... 
  case 102: ... 
  case 103: ... 
  case 104: ... 
  case 105: 
... 
  case 106: ... 
  case 107: ... 
}

If the above switch statement is broken down into two 
switch statements

switch (i) { 
  case 1: ... 
  case 2: ... 
  case 3: ... 
  case 
4: ... 
  case 5: ... 
  case 6: ... 
  case 7: ... 
}

and

switch (i) { 
  case 101: ... 
  case 102: ... 
  case 103: ... 
  
case 104: ... 
  case 105: ... 
  case 106: ... 
  case 107: ... 
}

then both the switch statements will be implemented 
using jump-tables whereas the unmodified switch 
statement will not be.



The pragma nojtbound can be used to turn off checking 
the jump table boundaries. It has no effect if a 
default label is supplied. Use of this pragma is 
dangerous: if the switch argument is not matched by a 
case statement the processor will happily jump into Nirvana.

8.1.8 Bit-shifting Operations.

Bit shifting is one of the most frequently used 
operation in embedded programming. SDCC tries to 
implement bit-shift operations in the most efficient 
way possible, e.g.:

unsigned char i;
... 
i >>= 4; 
...

generates the following code:

mov  a,_i 
swap a 
anl  a,#0x0f 
mov  _i,a

In general SDCC will never setup a loop if the shift 
count is known. Another example:

unsigned int i; 
... 
i >>= 9; 
...

will generate:

mov  a,(_i + 1) 
mov  (_i + 1),#0x00 
clr  c 
rrc  a 
mov  _i,a

8.1.9 Bit-rotation

A special case of the bit-shift operation is bit rotation
, SDCC recognizes the following expression to be a left 
bit-rotation:

unsigned  char i;           /* unsigned is needed for rotation */ 

... 
i = ((i << 1) | (i >> 7)); 
...

will generate the following code:

mov  a,_i 
rl   a 
mov  _i,a

SDCC uses pattern matching on the parse tree to 
determine this operation.Variations of this case will 
also be recognized as bit-rotation, i.e.: 

i = ((i >> 7) | (i << 1)); /* left-bit rotation */

8.1.10 Nibble and Byte Swapping

Other special cases of the bit-shift operations are 
nibble or byte swapping, SDCC recognizes the following 
expressions:

unsigned  char i; 
unsigned  int j; 
... 
i = ((i << 4) | (i 
>> 4)); 
j = ((j << 8) | (j >> 8)); 

and generates a swap instruction for the nibble swapping
 or move instructions for the byte swapping. The "j" 
example can be used to convert from little to 
big-endian or vice versa. If you want to change the 
endianness of a signed integer you have to cast to 
(unsigned int) first.

Note that SDCC stores numbers in little-endian

Usually 8-bit processors don't care much about 
endianness. This is not the case for the standard 8051 
which only has an instruction to increment its dptr
-datapointer so little-endian is the more efficient 
byte order.
 format (i.e. lowest order first).

8.1.11 Highest Order Bit / Any Order Bit

It is frequently required to obtain the highest order 
bit of an integral type (long, int, short or char 
types). Also obtaining any other order bit is not 
uncommon. SDCC recognizes the following expressions to 
yield the highest order bit and generates optimized 
code for it, e.g.:

unsigned int gint; 

foo () { 
  unsigned char hob1, aob1; 
  
bit hob2, hob3, aob2, aob3; 
  ... 
  hob1 = (gint >> 15) & 
1; 
  hob2 = (gint >> 15) & 1; 
  hob3 = gint & 0x8000; 
  aob1 
= (gint >> 9) & 1; 
  aob2 = (gint >> 8) & 1; 
  aob3 = gint 
& 0x0800; 
  .. 
}

will generate the following code:

                          61 ;  hob.c 7 
000A E5*01                62         mov   a,(_gint + 1) 
000C 23                   63        
 rl    a 
000D 54 01                64         anl   a,#0x01 
000F F5*02                65         mov   
_foo_hob1_1_1,a 
                          66 ;  hob.c 8 
0011 E5*01                67         mov   
a,(_gint + 1) 
0013 33                   68         rlc   a 
0014 92*00                69         mov   
_foo_hob2_1_1,c 
                          66 ;  hob.c 9 
0016 E5*01                67         mov   
a,(_gint + 1) 
0018 33                   68         rlc   a 
0019 92*01                69         mov   
_foo_hob3_1_1,c 
                          70 ;  hob.c 10 
001B E5*01                71         mov   
a,(_gint + 1) 
001D 03                   72         rr    a 
001E 54 01                73         anl   a,#0x01 

0020 F5*03                74         mov   _foo_aob1_1_1,a 
                          75 ;  hob.c 11 
0022 E5*01               
 76         mov   a,(_gint + 1) 
0024 13                   77         rrc   a 
0025 92*02                78         mov  
 _foo_aob2_1_1,c 
                          79 ;  hob.c 12 
0027 E5*01                80         mov   
a,(_gint + 1) 
0029 A2 E3                81         mov   c,acc[3] 
002B 92*03                82         mov  
 _foo_aob3_1_1,c 

Other variations of these cases however will not be 
recognized. They are standard C expressions, so I 
heartily recommend these be the only way to get the 
highest order bit, (it is portable). Of course it will 
be recognized even if it is embedded in other 
expressions, e.g.:

xyz = gint + ((gint >> 15) & 1);

will still be recognized.

8.1.12 Higher Order Byte / Higher Order Word

It is also frequently required to obtain a higher order 
byte or word of a larger integral type (long, int or 
short types). SDCC recognizes the following expressions 
to yield the higher order byte or word and generates 
optimized code for it, e.g.:

unsigned int gint; 
unsigned long int glong; 

foo () { 
  
unsigned char hob1, hob2; 
  unsigned int how1, how2; 
  ... 
  
hob1 = (gint >> 8) & 0xFF; 
  hob2 = glong >> 24; 
  how1 = 
(glong >> 16) & 0xFFFF; 
  how2 = glong >> 8; 
  .. 
}

will generate the following code:

                          91 ;  hob.c 15 
0037 85*01*06             92         mov   
_foo_hob1_1_1,(_gint + 1) 
                          93 ;  hob.c 16 
003A 85*05*07             94        
 mov   _foo_hob2_1_1,(_glong + 3) 
                          95 ;  hob.c 17 
003D 85*04*08            
 96         mov   _foo_how1_1_1,(_glong + 2) 
0040 85*05*09             97         mov   
(_foo_how1_1_1 + 1),(_glong + 3) 
0043 85*03*0A             98         mov   
_foo_how2_1_1,(_glong + 1) 
0046 85*04*0B             99         mov   
(_foo_how2_1_1 + 1),(_glong + 2) 

Again, variations of these cases may not be recognized. 
They are standard C expressions, so I heartily 
recommend these be the only way to get the higher order 
byte/word, (it is portable). Of course it will be 
recognized even if it is embedded in other expressions, e.g.:

xyz = gint + ((gint >> 8) & 0xFF);

will still be recognized.

8.1.13 Peephole Optimizer<sub:Peephole-Optimizer>

The compiler uses a rule based, pattern matching and 
re-writing mechanism for peep-hole optimization. It is 
inspired by copt a peep-hole optimizer by Christopher 
W. Fraser (cwfraser @ microsoft.com). A default set of 
rules are compiled into the compiler, additional rules 
may be added with the --peep-file <filename> option. 
The rule language is best illustrated with examples.

replace { 
  mov %1,a 
  mov a,%1
} by {
  mov %1,a
}

The above rule will change the following assembly sequence:

mov r1,a 
mov a,r1

to

mov r1,a

Note: All occurrences of a %n (pattern variable) must 
denote the same string. With the above rule, the 
assembly sequence:

mov r1,a 
mov a,r2

will remain unmodified.

Other special case optimizations 
may be added by the user (via --peep-file option). E.g. 
some variants of the 8051 MCU allow only ajmp and 
acall. The following two rules will change all ljmp and 
lcall to ajmp and acall

replace { lcall %1 } by { acall %1 } 
replace { ljmp %1 
} by { ajmp %1 }

(NOTE: from version 2.7.3 on, you can use option --acall-ajmp
, which also takes care of aligning the interrupt 
vectors properly.)


The inline-assembler code is also passed through the 
peep hole optimizer, thus the peephole optimizer can 
also be used as an assembly level macro expander. The 
rules themselves are MCU dependent whereas the rule 
language infra-structure is MCU independent. Peephole 
optimization rules for other MCU can be easily 
programmed using the rule language.

The syntax for a 
rule is as follows:

rule := replace [ restart ] '{' <assembly sequence> 
'\n' 
                            '}' by '{' '\n' 
                                
<assembly sequence> '\n' 
                            '}' [if 
<functionName> ] '\n' 

<assembly sequence> := assembly instruction (each 
instruction including labels must be on a separate line).


The optimizer will apply to the rules one by one from 
the top in the sequence of their appearance, it will 
terminate when all rules are exhausted. If the 
'restart' option is specified, then the optimizer will 
start matching the rules again from the top, this 
option for a rule is expensive (performance), it is 
intended to be used in situations where a 
transformation will trigger the same rule again. An 
example of this (not a good one, it has side effects) 
is the following rule:

replace restart { 
  pop %1 
  push %1 } by { 
  ; nop 
}

Note that the replace pattern cannot be a blank, but 
can be a comment line. Without the 'restart' option 
only the innermost 'pop' 'push' pair would be 
eliminated, i.e.:

pop ar1 
pop ar2 
push ar2 
push ar1

would result in:

pop ar1 
; nop 
push ar1

with the restart option the rule will be applied again 
to the resulting code and then all the pop-push pairs 
will be eliminated to yield:

; nop 
; nop

A conditional function can be attached to a rule. 
Attaching rules are somewhat more involved, let me 
illustrate this with an example.

replace { 
     ljmp %5 
%2:
} by { 
     sjmp %5 
%2:
} if labelInRange

The optimizer does a look-up of a function name table 
defined in function callFuncByName in the source file 
SDCCpeeph.c, with the name labelInRange. If it finds a 
corresponding entry the function is called. Note there 
can be no parameters specified for these functions, in 
this case the use of %5 is crucial, since the function 
labelInRange expects to find the label in that 
particular variable (the hash table containing the 
variable bindings is passed as a parameter). If you 
want to code more such functions, take a close look at 
the function labelInRange and the calling mechanism in 
source file SDCCpeeph.c. Currently implemented are 
labelInRange, labelRefCount, labelIsReturnOnly, 
operandsNotSame, xramMovcOption, 24bitMode, 
portIsDS390, 24bitModeAndPortDS390 and notVolatile.

I know this whole thing is a little kludgey, but maybe 
some day we will have some better means. If you are 
looking at this file, you will see the default rules 
that are compiled into the compiler, you can add your 
own rules in the default set there if you get tired of 
specifying the --peep-file option.

8.2 ANSI-Compliance<sub:ANSI-Compliance>

The latest publically available version of the standard 
ISO/IEC 9899 - Programming languages - C should be 
available at: [http://www.open-std.org/jtc1/sc22/wg14/www/standards.html#9899].


Deviations from the compliance:

* functions are not reentrant unless explicitly 
  declared as such or the --stack-auto command line 
  option is specified.

* structures and unions cannot be assigned values 
  directly, cannot be passed as function parameters or 
  assigned to each other and cannot be a return value 
  from a function, e.g.:

  struct s { ... }; 
struct s s1, s2; 
foo() 
{ 
    ... 
    s1 = 
  s2 ; /* is invalid in SDCC although allowed in ANSI 
  */ 
    ... 
}
struct s foo1 (struct s parms) /* invalid in 
  SDCC although allowed in ANSI */
{ 
    struct s rets; 
    ... 
    
  return rets; /* is invalid in SDCC although allowed 
  in ANSI */ 
}

* initialization of structure arrays must be fully braced.

  struct s { char x } a[] = {1, 2};     /* invalid in SDCC */

  struct s { char x } a[] = {{1}, {2}}; /* OK */

* 'long long' (64 bit integers) not supported.

* 'double' precision floating point not supported.

* Old K&R style function declarations are NOT allowed.

  foo(i,j) /* this old style of function declarations 
  */ 
int i,j; /* is valid in ANSI but not valid in SDCC 
  */ 
{ 
    ... 
}

* Most enhancements in C99 are not supported, e.g.:

  for (int i=0; i<10; i++) /* is invalid in SDCC 
  although allowed in C99 */

* But some have been added recently in SDCC 2.7.0. They 
  must be considered alpha quality however.

  inline int increment (int a) { return a+1; } /* 
  inlines the increment without function call overhead */

  int * restrict p; /* accepted but ignored */

* Certain words that are valid identifiers in the 
  standard may be reserved words in SDCC unless the --std-c89
   or --std-c99 command line options are used. These 
  may include (depending on the selected processor): 
  'at', 'banked', 'bit', 'code', 'critical', 'data', 
  'eeprom', 'far', 'flash', 'idata', 'interrupt', 
  'near', 'nonbanked', 'pdata', 'reentrant', 'sbit', 
  'sfr', 'shadowregs', 'sram', 'using', 'wparam', 
  'xdata', '_overlay', '_asm', '_endasm', and '_naked'. 
  Compliant equivalents of these keywords are always 
  available in a form that begin with two underscores, 
  f.e. '__data' instead of 'data'.

* Integer promotion of variable arguments is not 
  performed if the argument is explicitly taypecasted 
  unless the --std-c89 or --std-c99 command line 
  options are used.

  void vararg_func (char *str, ...) { str; }

void main (void)
{
  
  char c = 10;

  /* argument u is promoted to int before
   * 
  passing to function */
  vararg_func ("%c", c);

  /* 
  argument u is not promoted to int,
   * it is passed as 
  char to function
   * if --std-cXX is not defined;
   * is 
  promoted to int before passing
   * to function if 
  --std-cXX is defined */
  vararg_func ("%bc", (char)u);
}

8.3 Cyclomatic Complexity

Cyclomatic complexity of a function is defined as the 
number of independent paths the program can take during 
execution of the function. This is an important number 
since it defines the number test cases you have to 
generate to validate the function. The accepted 
industry standard for complexity number is 10, if the 
cyclomatic complexity reported by SDCC exceeds 10 you 
should think about simplification of the function 
logic. Note that the complexity level is not related to 
the number of lines of code in a function. Large 
functions can have low complexity, and small functions 
can have large complexity levels. 

SDCC uses the 
following formula to compute the complexity:


complexity = (number of edges in control flow graph) - 
(number of nodes in control flow graph) + 2;

Having said 
that the industry standard is 10, you should be aware 
that in some cases it be may unavoidable to have a 
complexity level of less than 10. For example if you 
have switch statement with more than 10 case labels, 
each case label adds one to the complexity level. The 
complexity level is by no means an absolute measure of 
the algorithmic complexity of the function, it does 
however provide a good starting point for which 
functions you might look at for further optimization.

8.4 Retargetting for other Processors

The issues for retargetting the compiler are far too 
numerous to be covered by this document. What follows 
is a brief description of each of the seven phases of 
the compiler and its MCU dependency.

* Parsing the source and building the annotated parse 
  tree. This phase is largely MCU independent (except 
  for the language extensions). Syntax & semantic 
  checks are also done in this phase, along with some 
  initial optimizations like back patching labels and 
  the pattern matching optimizations like bit-rotation etc.

* The second phase involves generating an intermediate 
  code which can be easy manipulated during the later 
  phases. This phase is entirely MCU independent. The 
  intermediate code generation assumes the target 
  machine has unlimited number of registers, and 
  designates them with the name iTemp. The compiler can 
  be made to dump a human readable form of the code 
  generated by using the --dumpraw option.

* This phase does the bulk of the standard 
  optimizations and is also MCU independent. This phase 
  can be broken down into several sub-phases:

Break down 
  intermediate code (iCode) into basic blocks.
Do 
  control flow & data flow analysis on the basic blocks.

  Do local common subexpression elimination, then 
  global subexpression elimination
Dead code elimination

  Loop optimizations
If loop optimizations caused any 
  changes then do 'global subexpression elimination' 
  and 'dead code elimination' again.

* This phase determines the live-ranges; by live range 
  I mean those iTemp variables defined by the compiler 
  that still survive after all the optimizations. Live 
  range analysis is essential for register allocation, 
  since these computation determines which of these 
  iTemps will be assigned to registers, and for how long.

* Phase five is register allocation. There are two 
  parts to this process.

The first part I call 'register 
  packing' (for lack of a better term). In this case 
  several MCU specific expression folding is done to 
  reduce register pressure.

The second part is more MCU 
  independent and deals with allocating registers to 
  the remaining live ranges. A lot of MCU specific code 
  does creep into this phase because of the limited 
  number of index registers available in the 8051.

* The Code generation phase is (unhappily), entirely 
  MCU dependent and very little (if any at all) of this 
  code can be reused for other MCU. However the scheme 
  for allocating a homogenized assembler operand for 
  each iCode operand may be reused.

* As mentioned in the optimization section the 
  peep-hole optimizer is rule based system, which can 
  reprogrammed for other MCUs.

More information is available on SDCC Wiki (preliminary 
link [http://sdcc.wiki.sourceforge.net/SDCC+internals+and+porting]) and in the thread [http://sf.net/mailarchive/message.php?msg_id=13954144] .

Compiler internals

9.1 The anatomy of the compiler<sub:The-anatomy-of>

This is an excerpt from an article published in Circuit 
Cellar Magazine in August 2000. It's a little outdated 
(the compiler is much more efficient now and 
user/developer friendly), but pretty well exposes the 
guts of it all.

The current version of SDCC can generate 
code for Intel 8051 and Z80 MCU. It is fairly easy to 
retarget for other 8-bit MCU. Here we take a look at 
some of the internals of the compiler. 

  Parsing 

Parsing the input source file and creating an AST 
(Annotated Syntax Tree). This phase also involves 
propagating types (annotating each node of the parse 
tree with type information) and semantic analysis. 
There are some MCU specific parsing rules. For example 
the storage classes, the extended storage classes are 
MCU specific while there may be a xdata storage class 
for 8051 there is no such storage class for z80 or 
Atmel AVR. SDCC allows MCU specific storage class 
extensions, i.e. xdata will be treated as a storage 
class specifier when parsing 8051 C code but will be 
treated as a C identifier when parsing z80 or ATMEL AVR 
C code.

  Generating iCode

Intermediate code generation. In this phase the AST is 
broken down into three-operand form (iCode). These 
three operand forms are represented as doubly linked 
lists. ICode is the term given to the intermediate form 
generated by the compiler. ICode example section shows 
some examples of iCode generated for some simple C 
source functions.

  Optimizations.

Bulk of the target independent optimizations is 
performed in this phase. The optimizations include 
constant propagation, common sub-expression 
elimination, loop invariant code movement, strength 
reduction of loop induction variables and dead-code elimination.

  Live range analysis

During intermediate code generation phase, the compiler 
assumes the target machine has infinite number of 
registers and generates a lot of temporary variables. 
The live range computation determines the lifetime of 
each of these compiler-generated temporaries. A picture 
speaks a thousand words. ICode example sections show 
the live range annotations for each of the operand. It 
is important to note here, each iCode is assigned a 
number in the order of its execution in the function. 
The live ranges are computed in terms of these numbers. 
The from number is the number of the iCode which first 
defines the operand and the to number signifies the 
iCode which uses this operand last.

  Register Allocation

The register allocation determines the type and number 
of registers needed by each operand. In most MCUs only 
a few registers can be used for indirect addressing. In 
case of 8051 for example the registers R0 & R1 can be 
used to indirectly address the internal ram and DPTR to 
indirectly address the external ram. The compiler will 
try to allocate the appropriate register to pointer 
variables if it can. ICode example section shows the 
operands annotated with the registers assigned to them. 
The compiler will try to keep operands in registers as 
much as possible; there are several schemes the 
compiler uses to do achieve this. When the compiler 
runs out of registers the compiler will check to see if 
there are any live operands which is not used or 
defined in the current basic block being processed, if 
there are any found then it will push that operand and 
use the registers in this block, the operand will then 
be popped at the end of the basic block. 

There are other MCU specific considerations in this 
phase. Some MCUs have an accumulator; very short-lived 
operands could be assigned to the accumulator instead 
of a general-purpose register.

  Code generation

Figure II gives a table of iCode operations supported 
by the compiler. The code generation involves 
translating these operations into corresponding 
assembly code for the processor. This sounds overly 
simple but that is the essence of code generation. Some 
of the iCode operations are generated on a MCU specific 
manner for example, the z80 port does not use registers 
to pass parameters so the SEND and RECV iCode 
operations will not be generated, and it also does not 
support JUMPTABLES. 


Figure II +--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

iCode                        | 

Operands                           | 

Description                                                                                                                                | 

C Equivalent                                                       |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

'!'                          | 

IC_LEFT() IC_RESULT()              | 

NOT operation                                                                                                                              | 

IC_RESULT = ! IC_LEFT;                                             |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

'~'                          | 

IC_LEFT() IC_RESULT()              | 

Bitwise complement of                                                                                                                      | 

IC_RESULT = ~IC_LEFT;                                              |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

RRC                          | 

IC_LEFT() IC_RESULT()              | 

Rotate right with carry                                                                                                                    | 

IC_RESULT = (IC_LEFT << 1) | (IC_LEFT >> (sizeof(IC_LEFT)*8-1));   |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

RLC                          | 

IC_LEFT() IC_RESULT()              | 

Rotate left with carry                                                                                                                     | 

IC_RESULT = (IC_LEFT << (sizeof(LC_LEFT)*8-1) ) | 
(IC_LEFT >> 1); |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

GETHBIT                      | 

IC_LEFT() IC_RESULT()              | 

Get the highest order bit of IC_LEFT                                                                                                       | 

IC_RESULT = (IC_LEFT >> (sizeof(IC_LEFT)*8 -1));                   |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

UNARYMINUS                   | 

IC_LEFT() IC_RESULT()              | 

Unary minus                                                                                                                                | 

IC_RESULT = - IC_LEFT;                                             |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

IPUSH                        | 

IC_LEFT()                          | 

Push the operand into stack                                                                                                                | 

NONE                                                               |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

IPOP                         | 

IC_LEFT()                          | 

Pop the operand from the stack                                                                                                             | 

NONE                                                               |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

CALL                         | 

IC_LEFT() IC_RESULT()              | 

Call the function represented by IC_LEFT                                                                                                   | 

IC_RESULT = IC_LEFT();                                             |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

PCALL                        | 

IC_LEFT() IC_RESULT()              | 

Call via function pointer                                                                                                                  | 

IC_RESULT = (*IC_LEFT)();                                          |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

RETURN                       | 

IC_LEFT()                          | 

Return the value in operand IC_LEFT                                                                                                        | 

return IC_LEFT;                                                    |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

LABEL                        | 

IC_LABEL()                         | 

Label                                                                                                                                      | 

IC_LABEL:                                                          |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

GOTO                         | 

IC_LABEL()                         | 

Goto label                                                                                                                                 | 

goto IC_LABEL();                                                   |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

'+'                          | 

IC_LEFT() IC_RIGHT() IC_RESULT()   | 

Addition                                                                                                                                   | 

IC_RESULT = IC_LEFT + IC_RIGHT                                     |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

'-'                          | 

IC_LEFT() IC_RIGHT() IC_RESULT()   | 

Subtraction                                                                                                                                | 

IC_RESULT = IC_LEFT - IC_RIGHT                                     |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

'*'                          | 

IC_LEFT() IC_RIGHT() IC_RESULT()   | 

Multiplication                                                                                                                             | 

IC_RESULT = IC_LEFT * IC_RIGHT;                                    |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

'/'                          | 

IC_LEFT() IC_RIGHT() IC_RESULT()   | 

Division                                                                                                                                   | 

IC_RESULT = IC_LEFT / IC_RIGHT;                                    |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

'%'                          | 

IC_LEFT() IC_RIGHT() IC_RESULT()   | 

Modulus                                                                                                                                    | 

IC_RESULT = IC_LEFT % IC_RIGHT;                                    |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

'<'                          | 

IC_LEFT() IC_RIGHT() IC_RESULT()   | 

Less than                                                                                                                                  | 

IC_RESULT = IC_LEFT < IC_RIGHT;                                    |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

'>'                          | 

IC_LEFT() IC_RIGHT() IC_RESULT()   | 

Greater than                                                                                                                               | 

IC_RESULT = IC_LEFT > IC_RIGHT;                                    |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

EQ_OP                        | 

IC_LEFT() IC_RIGHT() IC_RESULT()   | 

Equal to                                                                                                                                   | 

IC_RESULT = IC_LEFT == IC_RIGHT;                                   |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

AND_OP                       | 

IC_LEFT() IC_RIGHT() IC_RESULT()   | 

Logical and operation                                                                                                                      | 

IC_RESULT = IC_LEFT && IC_RIGHT;                                   |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

OR_OP                        | 

IC_LEFT() IC_RIGHT() IC_RESULT()   | 

Logical or operation                                                                                                                       | 

IC_RESULT = IC_LEFT || IC_RIGHT;                                   |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

'^'                          | 

IC_LEFT() IC_RIGHT() IC_RESULT()   | 

Exclusive OR                                                                                                                               | 

IC_RESULT = IC_LEFT ^ IC_RIGHT;                                    |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

'|'                          | 

IC_LEFT() IC_RIGHT() IC_RESULT()   | 

Bitwise OR                                                                                                                                 | 

IC_RESULT = IC_LEFT | IC_RIGHT;                                    |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

BITWISEAND                   | 

IC_LEFT() IC_RIGHT() IC_RESULT()   | 

Bitwise AND                                                                                                                                | 

IC_RESULT = IC_LEFT & IC_RIGHT;                                    |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

LEFT_OP                      | 

IC_LEFT() IC_RIGHT() IC_RESULT()   | 

Left shift                                                                                                                                 | 

IC_RESULT = IC_LEFT << IC_RIGHT                                    |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

RIGHT_OP                     | 

IC_LEFT() IC_RIGHT() IC_RESULT()   | 

Right shift                                                                                                                                | 

IC_RESULT = IC_LEFT >> IC_RIGHT                                    |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

GET_VALUE_
AT_ ADDRESS       | 

IC_LEFT() IC_RESULT()              | 

Indirect fetch                                                                                                                             | 

IC_RESULT = (*IC_LEFT);                                            |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

POINTER_SET                  | 

IC_RIGHT() IC_RESULT()             | 

Indirect set                                                                                                                               | 

(*IC_RESULT) = IC_RIGHT;                                           |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

'='                          | 

IC_RIGHT() IC_RESULT()             | 

Assignment                                                                                                                                 | 

IC_RESULT = IC_RIGHT;                                              |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

IFX                          | 

IC_COND IC_TRUE IC_LABEL           | 

Conditional jump. If true label is present then jump to 
true label if condition is true else jump to false 
label if condition is false   | 

if (IC_COND) goto IC_TRUE; 
  Or 
If (!IC_COND) goto IC_FALSE;     |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

ADDRESS_OF                   | 

IC_LEFT() IC_RESULT()              | 

Address of                                                                                                                                 | 

IC_RESULT = &IC_LEFT();                                            |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

JUMPTABLE                    | 

IC_JTCOND IC_JTLABELS              | 

Jump to list of labels depending on the value of JTCOND                                                                                    | 

Switch statement                                                   |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

CAST                         | 

IC_RIGHT() IC_LEFT() IC_RESULT()   | 

Cast types                                                                                                                                 | 

IC_RESULT = (typeof IC_LEFT) IC_RIGHT;                             |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

SEND                         | 

IC_LEFT()                          | 

This is used for passing parameters in registers; 
move 
IC_LEFT to the next available parameter register.                                 | 

None                                                               |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

RECV                         | 

IC_RESULT()                        | 

This is used for receiving parameters passed in registers;

Move the values in the next parameter register to 
IC_RESULT                   | 

None                                                               |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+
| 

(some more have been added)  | 

                                   | 

                                                                                                                                           | 

see f.e. gen51Code() in src/mcs51/gen.c                            |
+--------------------------------+--------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------+




  ICode Example

This section shows some details of iCode. The example C 
code does not do anything useful; it is used as an 
example to illustrate the intermediate code generated 
by the compiler.

1. xdata int * p;
2. int gint;
3. /* This function does 
nothing useful. It is used
4.    for the purpose of 
explaining iCode */
5. short function (data int *x)
6. {
7.   
short i=10;   /* dead initialization eliminated */
8.   short 
sum=10; /* dead initialization eliminated */
9.   short mul;
10.  
int j ;
11.  while (*x) *x++ = *p++; 
12.    sum = 0 ; 
13.  mul = 0;
14.  
/* compiler detects i,j to be induction variables */
15.  
for (i = 0, j = 10 ; i < 10 ; i++, j--) {
16.    sum += i;
17.    
mul += i * 3;   /* this multiplication remains */
18.    gint 
+= j * 3;  /* this multiplication changed to addition */
19.  }
20.  
return sum+mul;
21. }

In addition to the operands each iCode contains 
information about the filename and line it corresponds 
to in the source file. The first field in the listing 
should be interpreted as follows:
Filename(linenumber: 
iCode Execution sequence number : ICode hash table key 
: loop depth of the iCode).
Then follows the human 
readable form of the ICode operation. Each operand of 
this triplet form can be of three basic types a) 
compiler generated temporary b) user defined variable 
c) a constant value. Note that local variables and 
parameters are replaced by compiler generated 
temporaries. Live ranges are computed only for 
temporaries (i.e. live ranges are not computed for 
global variables). Registers are allocated for 
temporaries only. Operands are formatted in the 
following manner:
Operand Name [lr live-from : live-to ] 
{ type information } [ registers allocated ].
As 
mentioned earlier the live ranges are computed in terms 
of the execution sequence number of the iCodes, for 
example 
the iTemp0 is live from (i.e. first defined in 
iCode with execution sequence number 3, and is last 
used in the iCode with sequence number 5). For 
induction variables such as iTemp21 the live range 
computation extends the lifetime from the start to the 
end of the loop.
The register allocator used the live 
range information to allocate registers, the same 
registers may be used for different temporaries if 
their live ranges do not overlap, for example r0 is 
allocated to both iTemp6 and to iTemp17 since their 
live ranges do not overlap. In addition the allocator 
also takes into consideration the type and usage of a 
temporary, for example itemp6 is a pointer to near 
space and is used as to fetch data from (i.e. used in 
GET_VALUE_AT_ADDRESS) so it is allocated a pointer 
register (r0). Some short lived temporaries are 
allocated to special registers which have meaning to 
the code generator e.g. iTemp13 is allocated to a 
pseudo register CC which tells the back end that the 
temporary is used only for a conditional jump the code 
generation makes use of this information to optimize a 
compare and jump ICode.
There are several loop optimizations
 performed by the compiler. It can detect induction 
variables iTemp21(i) and iTemp23(j). Also note the 
compiler does selective strength reduction, i.e. the 
multiplication of an induction variable in line 18 
(gint = j * 3) is changed to addition, a new temporary 
iTemp17 is allocated and assigned a initial value, a 
constant 3 is then added for each iteration of the 
loop. The compiler does not change the multiplication 
in line 17 however since the processor does support an 
8 * 8 bit multiplication.
Note the dead code elimination 
optimization eliminated the dead assignments in line 7 
& 8 to I and sum respectively.


Sample.c (5:1:0:0) _entry($9) :

Sample.c(5:2:1:0) proc _function [lr0:0]{function short}

Sample.c(11:3:2:0) iTemp0 [lr3:5]{_near * int}[r2] = 
recv 

Sample.c(11:4:53:0) preHeaderLbl0($11) :

Sample.c(11:5:55:0) iTemp6 [lr5:16]{_near * int}[r0] := 
iTemp0 [lr3:5]{_near * int}[r2]

Sample.c(11:6:5:1) _whilecontinue_0($1) :

Sample.c(11:7:7:1) iTemp4 [lr7:8]{int}[r2 r3] = 
@[iTemp6 [lr5:16]{_near * int}[r0]]

Sample.c(11:8:8:1) if iTemp4 [lr7:8]{int}[r2 r3] == 0 
goto _whilebreak_0($3)

Sample.c(11:9:14:1) iTemp7 [lr9:13]{_far * int}[DPTR] 
:= _p [lr0:0]{_far * int}

Sample.c(11:10:15:1) _p [lr0:0]{_far * int} = _p 
[lr0:0]{_far * int} + 0x2 {short}

Sample.c(11:13:18:1) iTemp10 [lr13:14]{int}[r2 r3] = 
@[iTemp7 [lr9:13]{_far * int}[DPTR]]

Sample.c(11:14:19:1) *(iTemp6 [lr5:16]{_near * 
int}[r0]) := iTemp10 [lr13:14]{int}[r2 r3]

Sample.c(11:15:12:1) iTemp6 [lr5:16]{_near * int}[r0] = 
iTemp6 [lr5:16]{_near * int}[r0] + 0x2 {short}

Sample.c(11:16:20:1) goto _whilecontinue_0($1)

Sample.c(11:17:21:0)_whilebreak_0($3) :

Sample.c(12:18:22:0) iTemp2 [lr18:40]{short}[r2] := 0x0 {short}

Sample.c(13:19:23:0) iTemp11 [lr19:40]{short}[r3] := 
0x0 {short}

Sample.c(15:20:54:0)preHeaderLbl1($13) :

Sample.c(15:21:56:0) iTemp21 [lr21:38]{short}[r4] := 
0x0 {short}

Sample.c(15:22:57:0) iTemp23 [lr22:38]{int}[r5 r6] := 
0xa {int}

Sample.c(15:23:58:0) iTemp17 [lr23:38]{int}[r7 r0] := 
0x1e {int}

Sample.c(15:24:26:1)_forcond_0($4) :

Sample.c(15:25:27:1) iTemp13 [lr25:26]{char}[CC] = 
iTemp21 [lr21:38]{short}[r4] < 0xa {short}

Sample.c(15:26:28:1) if iTemp13 [lr25:26]{char}[CC] == 
0 goto _forbreak_0($7)

Sample.c(16:27:31:1) iTemp2 [lr18:40]{short}[r2] = 
iTemp2 [lr18:40]{short}[r2] + ITemp21 [lr21:38]{short}[r4]

Sample.c(17:29:33:1) iTemp15 [lr29:30]{short}[r1] = 
iTemp21 [lr21:38]{short}[r4] * 0x3 {short}

Sample.c(17:30:34:1) iTemp11 [lr19:40]{short}[r3] = 
iTemp11 [lr19:40]{short}[r3] + iTemp15 [lr29:30]{short}[r1]

Sample.c(18:32:36:1:1) iTemp17 [lr23:38]{int}[r7 r0]= 
iTemp17 [lr23:38]{int}[r7 r0]- 0x3 {short}

Sample.c(18:33:37:1) _gint [lr0:0]{int} = _gint 
[lr0:0]{int} + iTemp17 [lr23:38]{int}[r7 r0]

Sample.c(15:36:42:1) iTemp21 [lr21:38]{short}[r4] = 
iTemp21 [lr21:38]{short}[r4] + 0x1 {short}

Sample.c(15:37:45:1) iTemp23 [lr22:38]{int}[r5 r6]= 
iTemp23 [lr22:38]{int}[r5 r6]- 0x1 {short}

Sample.c(19:38:47:1) goto _forcond_0($4)

Sample.c(19:39:48:0)_forbreak_0($7) :

Sample.c(20:40:49:0) iTemp24 [lr40:41]{short}[DPTR] = 
iTemp2 [lr18:40]{short}[r2] + ITemp11 [lr19:40]{short}[r3]

Sample.c(20:41:50:0) ret iTemp24 [lr40:41]{short}

Sample.c(20:42:51:0)_return($8) :

Sample.c(20:43:52:0) eproc _function [lr0:0]{ ia0 re0 
rm0}{function short}

Finally the code generated for this function:


.area DSEG (DATA)

_p::

  .ds 2

_gint::

  .ds 2

; sample.c 5

; ----------------------------------------------

; function function

; ----------------------------------------------

_function:

; iTemp0 [lr3:5]{_near * int}[r2] = recv 

  mov r2,dpl

; iTemp6 [lr5:16]{_near * int}[r0] := iTemp0 
[lr3:5]{_near * int}[r2]

  mov ar0,r2

;_whilecontinue_0($1) :

00101$:

; iTemp4 [lr7:8]{int}[r2 r3] = @[iTemp6 [lr5:16]{_near 
* int}[r0]]

; if iTemp4 [lr7:8]{int}[r2 r3] == 0 goto _whilebreak_0($3)

  mov ar2,@r0

  inc r0

  mov ar3,@r0

  dec r0

  mov a,r2

  orl a,r3

  jz 00103$

00114$:

; iTemp7 [lr9:13]{_far * int}[DPTR] := _p [lr0:0]{_far 
* int}

  mov dpl,_p

  mov dph,(_p + 1)

; _p [lr0:0]{_far * int} = _p [lr0:0]{_far * int} + 0x2 {short}

  mov a,#0x02

  add a,_p

  mov _p,a

  clr a

  addc a,(_p + 1)

  mov (_p + 1),a

; iTemp10 [lr13:14]{int}[r2 r3] = @[iTemp7 
[lr9:13]{_far * int}[DPTR]]

  movx a,@dptr

  mov r2,a

  inc dptr

  movx a,@dptr

  mov r3,a

; *(iTemp6 [lr5:16]{_near * int}[r0]) := iTemp10 
[lr13:14]{int}[r2 r3]

  mov @r0,ar2

  inc r0

  mov @r0,ar3

; iTemp6 [lr5:16]{_near * int}[r0] = 

; iTemp6 [lr5:16]{_near * int}[r0] + 

; 0x2 {short}

  inc r0

; goto _whilecontinue_0($1)

  sjmp 00101$

; _whilebreak_0($3) :

00103$:

; iTemp2 [lr18:40]{short}[r2] := 0x0 {short}

  mov r2,#0x00

; iTemp11 [lr19:40]{short}[r3] := 0x0 {short}

  mov r3,#0x00

; iTemp21 [lr21:38]{short}[r4] := 0x0 {short}

  mov r4,#0x00

; iTemp23 [lr22:38]{int}[r5 r6] := 0xa {int}

  mov r5,#0x0A

  mov r6,#0x00

; iTemp17 [lr23:38]{int}[r7 r0] := 0x1e {int}

  mov r7,#0x1E

  mov r0,#0x00

; _forcond_0($4) :

00104$:

; iTemp13 [lr25:26]{char}[CC] = iTemp21 
[lr21:38]{short}[r4] < 0xa {short}

; if iTemp13 [lr25:26]{char}[CC] == 0 goto _forbreak_0($7)

  clr c

  mov a,r4

  xrl a,#0x80

  subb a,#0x8a

  jnc 00107$

00115$:

; iTemp2 [lr18:40]{short}[r2] = iTemp2 
[lr18:40]{short}[r2] + 

; iTemp21 [lr21:38]{short}[r4]

  mov a,r4

  add a,r2

  mov r2,a

; iTemp15 [lr29:30]{short}[r1] = iTemp21 
[lr21:38]{short}[r4] * 0x3 {short}

  mov b,#0x03

  mov a,r4

  mul ab

  mov r1,a

; iTemp11 [lr19:40]{short}[r3] = iTemp11 
[lr19:40]{short}[r3] + 

; iTemp15 [lr29:30]{short}[r1]

  add a,r3

  mov r3,a

; iTemp17 [lr23:38]{int}[r7 r0]= iTemp17 
[lr23:38]{int}[r7 r0]- 0x3 {short}

  mov a,r7

  add a,#0xfd

  mov r7,a

  mov a,r0

  addc a,#0xff

  mov r0,a

; _gint [lr0:0]{int} = _gint [lr0:0]{int} + iTemp17 
[lr23:38]{int}[r7 r0]

  mov a,r7

  add a,_gint

  mov _gint,a

  mov a,r0

  addc a,(_gint + 1)

  mov (_gint + 1),a

; iTemp21 [lr21:38]{short}[r4] = iTemp21 
[lr21:38]{short}[r4] + 0x1 {short}

  inc r4

; iTemp23 [lr22:38]{int}[r5 r6]= iTemp23 
[lr22:38]{int}[r5 r6]- 0x1 {short}

  dec r5

  cjne r5,#0xff,00104$

  dec r6

; goto _forcond_0($4)

  sjmp 00104$

; _forbreak_0($7) :

00107$:

; ret iTemp24 [lr40:41]{short}

  mov a,r3

  add a,r2

  mov dpl,a

; _return($8) :

00108$:

  ret


9.2 A few words about basic block successors, 
  predecessors and dominators

Successors are basic blocks that might execute after 
this basic block.
Predecessors are basic blocks that 
might execute before reaching this basic block.

Dominators are basic blocks that WILL execute before 
reaching this basic block.


[basic block 1]

if (something)

    [basic block 2]

else

    [basic block 3]

[basic block 4]


a) succList of [BB2] = [BB4], of [BB3] = [BB4], of 
[BB1] = [BB2,BB3]

b) predList of [BB2] = [BB1], of [BB3] = [BB1], of 
[BB4] = [BB2,BB3]

c) domVect of [BB4] = BB1 ... here we are not sure if 
BB2 or BB3 was executed but we are SURE that BB1 was executed.

Acknowledgments

[http://sdcc.sourceforge.net/#Who]

Thanks to all the other volunteer developers who have 
helped with coding, testing, web-page creation, 
distribution sets, etc. You know who you are :-)

Thanks 
to Sourceforge [http://www.sf.net] which has hosted the project since 1999 
and donates significant download bandwidth.

Also thanks 
to all SDCC Distributed Compile Farm members for 
donating CPU cycles and bandwidth for snapshot builds.


This document was initially written by Sandeep Dutta

All product names mentioned herein may be trademarks of 
their respective companies. 

 Alphabetical index

To avoid confusion, the installation and building 
options for SDCC itself (chapter 2) are not part of the index.


