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 <linuxdoc>
 <title>SDCC Compiler User Guide
 </title>
 <author>Sandeep Dutta (sandeep.dutta@usa.net)
 </author>
 <sect>Introduction
 <p>SDCC is a Free ware , retargettable, optimizing ANSI-C compiler. The current
 version targets Intel 8051 based MCUs, it can be retargetted for other 8 bit
 MCUs or PICs. The entire source code for the compiler is distributed under
 GPL. SDCC used ASXXXX &amp; ASLINK a Free ware, retargettable assembler &amp;
 linker. SDCC has extensive MCU (8051) specific language extensions, which lets
 it utilize the underlying hardware effectively. The front-end (parser) will
 be enhanced to handle language extensions for other MCUs as and when they are
 targetted. 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 &amp; propagation, copy propagation, dead code elimination
 and jumptables 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 short (8 bits, 1 byte), char (8 bits,
 1 byte), int (16 bits, 2 bytes ), long (32 bit, 4 bytes) &amp; float (4 byte
 IEEE). 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 to report the relative complexity of a function,
 these functions can then be further optimized , or hand coded in assembly if
 need be. SDCC also comes with a companion source level debugger SDCDB, the
 debugger currently uses S51 a freeware simulator for 8051, it can be easily
 modified to use other simulators. The latest version can be downloaded from
 <bf>http://www.geocities.com/ResearchTriangle/Forum/1353</bf>
 </p>
 <p>All packages used in this compiler system are opensource (freeware); source
 code for all the sub-packages ( asxxxx assembler/linker , pre-processor and
 gc a conservative garbage collector) are distributed with the package. Documentation
 was created using a freeware word processor (LyX). 
 </p>
 <p>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!
 
 </p>
 <sect>Installation <label id="Installation" >
 <p>What you need before you start installation of SDCC ? A C Compiler, not
 just any C Compiler, gcc to be exact, you can get adventurous and try another
 compiler , I HAVEN'T tried it. GCC is free , and is available for almost all
 major platforms, if you are using linux you probably already have it, if you
 are using Windows 95/NT go to www.cygnus.com and download CYGWIN32 you will
 need the full development version of their tool (full.exe), follow their instructions
 for installation (this is also free and is very easy to install), Windows 95/NT
 users be aware that the compiler runs substantially slower on the Windows platform,
 I am not sure why.
 </p>
 <p>After you have installed gcc you are ready to build the compiler (sorry
 no binary distributions yet). SDCC is native to Linux but can be ported to
 any platform on which GCC is available . Extract the source file package (.zip
 or .tar.gz) into some directory , which we shall refer to as SDCCDIR from now
 on.
 </p>
 <sect1>Components of SDCC<label id="Components" >
 <sect2>gc ( a conservative garbage collector)
 <p>SDCC relies on this component to do all the memory management, this excellent
 package is copyrighted by Jans J Boehm(boehm@sgi.com) and Alan J Demers but
 can be used with minimum restrictions. The GC source will be extracted into
 the directory SDCCDIR/gc. 
 </p>
 <sect2>cpp ( C-Preprocessor)
 <p>The preprocessor is extracted into the directory SDCCDIR/cpp, it is a modified
 version of the GNU preprocessor.
 </p>
 <sect2>asxxxx &amp; aslink ( The assembler and Linkage Editor)
 <p>This is retargettable assembler &amp; linkage editor, it was developed
 by Alan Baldwin, John Hartman created the version for 8051, and I (Sandeep)
 have some enhancements and bug fixes for it to work properly with the SDCC.
 This component is extracted into the directory SDCCDIR/asxxxx.
 </p>
 <sect2>SDCC - The compiler.
 <p>This is the actual compiler, it uses gc and invokes the assembler and linkage
 editor. All files with the prefix SDCC are part of the compiler and is extracted
 into the the directory SDCCDIR.
 </p>
 <sect2>S51 - Simulator
 <p>Version 2.1.8 onwards contains s51 a freeware , opensource simulator developed
 by Daniel Drotos &lt;drdani@mazsola.iit.uni-miskolc.hu&gt;. The executable
 is built as part of build process, for more information visit Daniel's website
 at &lt;http://mazsola.iit.uni-miskolc.hu/&tilde;drdani/embedded/s51/&gt;.
 </p>
 <sect2>SDCDB - Source level Debugger.
 <p>SDCDB is the companion source level debugger . The current version of the
 debugger uses Daniel's Simulator S51, but can be easily changed to use other
 simulators.
 </p>
 <sect1>Installation for Version &lt;= 2.1.7
 <p>After the package is extracted (Windows 95/NT users start CYGWIN shell),
 change to the directory where you extracted the package and give the command.
 </p>
 <p>
 <verb>./sdccbuild.sh
 </verb></p>
 <p>This is a bash shell script, it will compile all the above mentioned components
 and install the executables into the directory SDCCDIR/bin make sure you add
 this directory to your PATH environment variable. This script will also compile
 all the support routines ( library routines ) using SDCC. The support routines
 are all developed in C and need to be compiled.
 </p>
 <sect1>Installation for Version &gt;= 2.1.8a
 <p>The distribution method from Version 2.1.8a has been changed to be conforment
 with the "autoconf" utility. The source is now distributed as <bf>sdcc-&lt;version
 number&gt;.tar.gz format</bf> , instead of the older .zip format. The steps for
 installation are as follows.
 </p>
 <sect2>Unpack the sources.
 <p>This is usually done by the following command "<bf>gunzip -c sdcc-&lt;version
 number&gt;.tar.gz | tar -xv -</bf>"
 </p>
 <sect2>Change to the main source directory (usually sdcc or sdcc-&lt;version number&gt;)
 <sect2>Issue command to configure your system
 <p>The configure command has several options the most commonly used option
 is --prefix=&lt;directory name&gt;, where &lt;directory name&gt; is the final
 location for the sdcc executables and libraries, (default location is /usr/local).
 The installation process will create the following directory structure under
 the &lt;directory name&gt; specified.
 </p>
 <p>
 <verb>bin/ - binary exectables (add to PATH environment variable) 
share/ 
      sdcc51inc/
 - include header files 
      sdcc51lib/ - 
             small/ - Object &amp;
 Library files for small model library 
             large/ - Object &amp; library
 files for large model library
 </verb></p>
 <p>The command 
 </p>
 <p><bf>'./configure --prefix=/usr/local" </bf>
 </p>
 <p>will create configure the compiler to be installed in directory /usr/local/bin.
 </p>
 <sect2>make
 <p>After configuration step issue the command 
 </p>
 <p><bf>"make"</bf>
 </p>
 <p>This will compile the compiler
 </p>
 <sect2>"make install"
 <p>Will install the compiler and libraries in the appropriate directories.
 </p>
 <sect2>Special Notes for Windows Users. Provided by Michael Jamet&lsqb; mjamet@computer.org&rsqb;
 
 <p> 
 </p>
 <p>  How to install SDCC from source on a Windows 95 or Windows NT 4 system
 
 </p>
 <p> 
 </p>
 <p>  This document describes how to install SDCC on a Win 95 or Win NT 4 system.
 
 </p>
 <p>  These instructions probably work for Win 98 as well, but have not been
 
 </p>
 <p>  tested on that platform. 
 </p>
 <p> 
 </p>
 <p>  There are lots of little differences between UNIX and the Win32 Cygnus
 
 </p>
 <p>  environment which make porting more difficult than it should be.  If
 
 </p>
 <p>  you want the details, please contact me.  Otherwise just follow these
 
 </p>
 <p>  instructions. 
 </p>
 <p> 
 </p>
 <p>  1. Install the Cygnus Software 
 </p>
 <p>  Go to http://sourceware.cygnus.com/cygwin.  Cygnus provides a UNIX like
 
 </p>
 <p>  environment for Win 32 systems.  Download &dquot;full.exe&dquot; and
 install.  You 
 </p>
 <p>  MUST install it on your C drive.  &dquot;full.exe&dquot; contains a shell
 AND many 
 </p>
 <p>  common UNIX utilities. 
 </p>
 <p> 
 </p>
 <p>  2. Download and Extract the Latest SDCC 
 </p>
 <p>  The latest version can be found at 
 </p>
 <p>   www.geocities.com/ResearchTriange/Forum/1353. 
 </p>
 <p>  It can be uncompressed with winzip. 
 </p>
 <p> 
 </p>
 <p>  3.  Start a Cygnus Shell 
 </p>
 <p>  There should be an entry in the Start Menu for Cygnus.  Invoke the shell.
 
 </p>
 <p>  This gives you a UNIX like environment.  FROM THIS POINT ON, DIRECTORIES
 
 </p>
 <p>  MUST BE SPECIFIED WITH FORWARD SLASHES (/) NOT THE DOS STYLE BACK 
 </p>
 <p>  SLASHES (&bsol;) BECAUSE THIS IS WHAT UNIX EXPECTS.  - 
 </p>
 <p>   ex. &dquot;&bsol;winnt&dquot; would be &dquot;/winnt&dquot; under the
 shell. 
 </p>
 <p> 
 </p>
 <p>  4. Change Directory to Where SDCC was extracted (referred to as INSTALLDIR)
 
 </p>
 <p> 
 </p>
 <p>  ex. cd /sdcc218Da.  If you extracted to a drive OTHER THAN C, the drive
 
 </p>
 <p>  must be specified as part of the path. For example, if you extracted
 to 
 </p>
 <p>  your &dquot;g drive&dquot;, type the following: &dquot;cd //g/mydir&dquot;. 
 You must use &dquot;//&dquot; 
 </p>
 <p>  to specify the drive. 
 </p>
 <p> 
 </p>
 <p>  5. Make Dirs Which are Automatically Made During the UNIX Installation
 
 </p>
 <p>  From the INSTALLDIR, 
 </p>
 <p> 
 </p>
 <p>   mkdir -p bin   (not a typo, just &dquot;bin&dquot;) 
 </p>
 <p>   mkdir -p /bin 
 </p>
 <p>   mkdir -p /usr/local/bin 
 </p>
 <p>   mkdir -p /usr/local/share 
 </p>
 <p>   mkdir -p /usr/local/share/sdcc51lib 
 </p>
 <p>   mkdir -p /usr/local/share/sdcc51inc 
 </p>
 <p>   mkdir -p /tmp 
 </p>
 <p> 
 </p>
 <p>  (When a path from the root directory is specified WITHOUT a drive, the
 
 </p>
 <p>  drive defaults to c.  For example /michael/newuser =&gt; c:&bsol;michael&bsol;newuser)
 
 </p>
 <p> 
 </p>
 <p>  6.  Add Programs to /bin Expected by the Installation Process 
 </p>
 <p>   - Look at your path: echo &dollar;PATH 
 </p>
 <p>     One of the fields is the diretory with the CYGNUS programs. 
 </p>
 <p>    ex. /CYGNUS/CYGWIN&tilde;1/H-I586/BIN 
 </p>
 <p> 
 </p>
 <p>   - cd to the directory found above.  You may have to fiddle with the
 
 </p>
 <p>     case (upper or lower) here because the PATH is SHOWN as all upper
 
 </p>
 <p>     case, but is actually mixed.  To help you along, you may type 
 </p>
 <p>     a letter or 2 followed by the escape key.  The shell will fill 
 </p>
 <p>     out the remaining letters IF THEY describe a unique directory. 
 </p>
 <p>     If you have problems here, cd one directory and type &dquot;ls&dquot;. 
 &dquot;ls&dquot; 
 </p>
 <p>     is the equivalent of &dquot;dir/w&dquot;. 
 </p>
 <p> 
 </p>
 <p>   - Copy the following: 
 </p>
 <p>    cp sh.exe /bin 
 </p>
 <p>    cp pwd.exe /bin 
 </p>
 <p>    cp echo.exe /bin 
 </p>
 <p> 
 </p>
 <p>  7. Go back to the INSTALLDIR 
 </p>
 <p>   cd INSTALLDIR 
 </p>
 <p>  ex. cd //d/sdcc218Da 
 </p>
 <p> 
 </p>
 <p>  8. Run the configure Program 
 </p>
 <p>   ./configure 
 </p>
 <p>  The &dquot;./&dquot; is important because your current directory is NOT
 in your path. 
 </p>
 <p>  Under DOS, your current directory was implicitly always the first entry
 
 </p>
 <p>  in your path. 
 </p>
 <p> 
 </p>
 <p>  9. Run make 
 </p>
 <p>   make 
 </p>
 <p> 
 </p>
 <p>  This process takes quite some time under Win 32. 
 </p>
 <p> 
 </p>
 <p>  10. Install the Newly Built Software 
 </p>
 <p>   make install 
 </p>
 <p> 
 </p>
 <p>  This will partially install the software into the /usr/local directories
 
 </p>
 <p>  created in step 5.  What it actually doing is copying the .c, .h and
 
 </p>
 <p>  library files to directories under /usr/local/share. 
 </p>
 <p> 
 </p>
 <p>  It will NOT be able to install the actual programs (binaries) because
 
 </p>
 <p>  it does not know programs on Win32 systems have &dquot;.exe&dquot; extensions.
 
 </p>
 <p>  For example, it tries to install sdcc instead of sdcc.exe. 
 </p>
 <p> 
 </p>
 <p>  After the automated part is finished, you must manually copy the binaries:
 
 </p>
 <p>   cd bin  (This is the bin directory in your INSTALLDIR) 
 </p>
 <p>   cp * /usr/local/bin 
 </p>
 <p> 
 </p>
 <p>  11. Make sure /usr/local/bin is in Your PATH 
 </p>
 <p>  You may add c:&bsol;usr&bsol;local&bsol;bin to your path however your
 Win32 system allows.  For 
 </p>
 <p>  example you may add it to the PATH statement in autoexec.bat. 
 </p>
 <p> 
 </p>
 <p>  Good luck.  If you have any questions send them to me or post them 
 </p>
 <p>  to the list. 
 </p>
 <sect>Compiling.<label id="Compiling" >
 <sect1>Single Source file projects.<label id="One Source File" >
 <p>For single source file projects the process is very simple. Compile your
 programs with the following command
 </p>
 <p>
 <verb>sdcc sourcefile.c
 </verb></p>
 <p>The above command will compile ,assemble and link your source file. Output
 files are as follows.
 </p>
 <p>
 <itemize>
  <item>sourcefile.asm - Assembler source file created by the compiler
  <item>sourcefile.lst - Assembler listing file created by the Assembler
  <item>sourcefile.rst - Assembler listing file updated with linkedit information
 , created by linkage editor
  <item>sourcefile.sym - symbol listing for the sourcefile, created by the assembler.
  <item>sourcefile.rel - Object file created by the assembler, input to Linkage
 editor.
  <item>sourcefile.map - The memory map for the load module, created by the Linker.
  <item>sourcefile.&lt;ihx | s19&gt; - The load module : ihx - Intel hex format
 (default ), s19 - Motorola S19 format when compiler option --out-fmt-s19 is
 used.
 </itemize></p>
 <sect1>Projects with multiple source files.
 <p>SDCC can compile only ONE file at a time. Let us for example assume that
 you have a project containing the following files.
 </p>
 <p>
 <verb>foo1.c ( contains some functions )foo2.c (contains some more functions)foomain.c (contains more functions and the function main)
 </verb></p>
 <p>The first two files will need to be compiled separately with the commands
 </p>
 <p>
 <verb>sdcc -c foo1.csdcc -c foo2.c
 </verb></p>
 <p>Then compile the source file containing main and link the other files together
 with the following command.
 </p>
 <p>
 <verb>sdcc foomain.c foo1.rel foo2.rel
 </verb></p>
 <p>Alternatively foomain.c can be separately compiled as well
 </p>
 <p>
 <verb>sdcc -c foomain.c sdcc foomain.rel foo1.rel foo2.rel
 </verb></p>
 <p>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.
 </p>
 <sect1>Projects with additional libraries.
 <p>Some reusable routines may be compiled into a library, see the documentation
 for the assembler and linkage editor in the directory SDCCDIR/asxxxx/asxhtm.htm
 this describes how to create a .lib library file, the libraries created in
 this manner may be included using the command line, make sure you include the
 -L &lt;library-path&gt; option to tell the linker where to look for these files.
 Here is an example, assuming you have the source file 'foomain.c' and a library
 'foolib.lib' in the directory 'mylib'.
 </p>
 <p>
 <verb>sdcc foomain.c foolib.lib -L mylib
 </verb></p>
 <p>Note here that 'mylib' must be an absolute path name.
 </p>
 <p>The view of the way the linkage editor processes the library files, it
 is recommended that you put each source routine in a separate file and combine
 them using the .lib file. For an example see the standard library file 'libsdcc.lib'
 in the directory SDCCDIR/sdcc51lib.
 </p>
 <sect>Command Line options<label id="Command Line Options" >
 <p>
 <itemize>
  <item><bf>--model-large<label id="--model-large" ></bf> Generate code for Large model programs see section Memory
 Models for more details. If this option is used all source files in the project
 should be compiled with this option. In addition the standard library routines
 are compiled with small model , they will need to be recompiled.
  <item><bf>--model-small</bf> <label id="--model-small" >Generate code for Small Model programs see section Memory
 Models for more details. This is the default model.
  <item><bf>--model-flat24</bf> <ref id="--model-flat24" name="--model-flat24" >Generate code for Small Model programs see section Memory
 Models for more details. This is the default model.
  <item><bf>--stack-auto</bf> <label id="--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 Parameters and Local Variables for more details. If this option is
 used all source files in the project should be compiled with this option. 
  <item><bf>--xstack</bf><label id="--xstack" > Uses a pseudo stack in the first 256 bytes in the external ram
 for allocating variables and passing parameters. See section on external stack
 for more details.
  <item><bf>--nogcse</bf><label id="--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. A warning message will be generated when this happens
 and the compiler will indicate the number of extra bytes it allocated. It recommended
 that this option NOT be used , &num;pragma NOGCSE can be used to turn off global
 subexpression elimination for a given function only.
  <item><bf>--noinvariant</bf><label id="--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 section Loop Invariants.It recommended that this
 option NOT be used , &num;pragma NOINVARIANT can be used to turn off invariant
 optimizations for a given function only.
  <item><bf>--noinduction</bf><label id="--noinduction" > Will not do loop induction optimizations, see section Strength
 reduction for more details.It recommended that this option NOT be used , &num;pragma
 NOINDUCTION can be used to turn off induction optimizations for given function
 only.
  <item><bf>--nojtbound </bf><label id="--nojtbound" > Will not generate boundary condition check when switch statements
 are implemented using jump-tables. See section Switch Statements for more details.It
 recommended that this option NOT be used , &num;pragma NOJTBOUND can be used
 to turn off boundary checking for jump tables for a given function only.
  <item><bf>--noloopreverse</bf> <label id="--noloopreverse" >Will not do loop reversal optimization
  <item><bf>--noregparms</bf><label id="--noregparms" > By default the first parameter is passed using global registers
 (DPL,DPH,B,ACC). This option will disable parameter passing using registers.
 NOTE: if your program uses the 16/32 bit support routines (for multiplication/division)
 these library routines will need to be recompiled with the --noregparms option
 as well.
  <item><bf>--callee-saves function1&lsqb;,function2&rsqb;&lsqb;,function3&rsqb;....</bf>
 <label id="--callee-saves" >The compiler by default uses a caller saves convention for register saving
 across function calls, however this can cause unneccessary register pushing
 &amp; 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,
 extra code will be generated at the entry &amp; exit for these functions to
 save &amp; restore the registers used by these functions, this can SUBSTANTIALLY
 reduce code &amp; improve run time performance of the generated code. In future
 the compiler (with interprocedural 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 _muluint..., 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 Directive<ref id="Pragmaa" name="" > CALLEE-SAVES.<ref id="pragma callee-saves" name="" > .
  <item><bf>--debug </bf><label id="--debug" >When this option is used the compiler will generate debug information
 , that can be used with the SDCDB. The debug information is collected in a
 file with .cdb extension. For more information see documentation for SDCDB.
  <item><bf>--regextend </bf><label id="--regextend" > This option will cause the compiler to define pseudo registers
 , if this option is used, all source files in the project should be compiled
 with this option. See section Register Extension for more details.
  <item><bf>--compile-only</bf>(-c) <label id="--compile-only" > will compile and assemble the source only, will not
 call the linkage editor.
  <item><bf>--xram-loc </bf><label id="--xram-loc" >&lt;Value&gt; The start location of the external ram, default
 value is 0. The value entered can be in Hexadecimal or Decimal format .eg.
 --xram-loc 0x8000 or --xram-loc 32768.
  <item><bf>--code-loc </bf><label id="--code-loc" >&lt;Value&gt; 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
 .eg. --code-loc 0x8000 or --code-loc 32768.
  <item><bf>--stack-loc</bf><label id="--stack-loc" >&lt;Value&gt; The initial value of the stack pointer. The default
 value of the stack pointer is 0x07 if only register bank 0 is used, if other
 register banks are used then the stack pointer is initialized to the location
 above the highest register bank used. eg. if register banks 1 &amp; 2 are used
 the stack pointer will default to location 0x18. The value entered can be in
 Hexadecimal or Decimal format .eg. --stack-loc 0x20 or --stack-loc 32. If all
 four register banks are used the stack will be placed after the data segment
 (equivalent to --stack-after-data)
  <item><bf>--stack-after-data</bf><label id="--stack-after-data" >This option will cause the stack to be located in the
 internal ram after the data segment.
  <item><bf>--data-loc</bf> <label id="--data-loc" >&lt;Value&gt; The start location of the internal ram data segment,
 the default value is 0x30.The value entered can be in Hexadecimal or Decimal
 format .eg. --data-loc 0x20 or --data-loc 32.
  <item><bf>--idata-loc</bf><label id="--idata-loc" >&lt;Value&gt; The start location of the indirectly addressable
 internal ram, default value is 0x80. The value entered can be in Hexadecimal
 or Decimal format .eg. --idata-loc 0x88 or --idata-loc 136.
  <item><bf>--peep-file<label id="--peep-file" > </bf>&lt;filename&gt; This option can be used to use additional
 rules to be used by the peep hole optimizer. See section Peep Hole optimizations
 for details on how to write these rules.
  <item><bf>--lib-path (-L) </bf><label id="--lib-path" >&lt;absolute path to additional libraries&gt; This option
 is passed to the linkage editor, 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.
  <item><bf>-I &lt;path&gt;<label id="-I" ></bf> The additional location where the pre processor will look
 for &lt;..h&gt; or "..h" files.
  <item><bf>-D&lt;macro&lsqb;=value&rsqb;&gt;</bf> <label id="-D" >Command line definition of macros. Passed
 to the pre processor.
  <item><bf>-E</bf><label id="-E" > Run only the C preprocessor. Preprocess all the C source files specified
 and output the results to standard output.
  <item><bf>-M<label id="-M" ></bf> 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 `&num;include'd in it. This rule
 may be a single line or may be continued with `&bsol;'-newline if it is long.
 The list of rules is printed on standard output instead of the preprocessed
 C program. `-M' implies `-E'.
  <item><bf>-C</bf> <label id="-C" >Tell the preprocessor not to discard comments. Used with the `-E' option.
  <item><bf>-MM </bf><label id="-MM" >Like `-M' but the output mentions only the user header files included
 with `&num;include file&dquot;'. System header files included with `&num;include
 &lt;file&gt;' are omitted.
  <item><bf>-Aquestion(answer)</bf><label id="-Aquestion(answer)" > Assert the answer answer for question, in case it is
 tested with a preprocessor conditional such as `&num;if &num;question(answer)'.
 `-A-' disables the standard asser- tions that normally describe the target
 machine.
  <item><bf>-Aquestion</bf><label id="-Aquestion" > (answer) Assert the answer answer for question, in case it is
 tested with a preprocessor conditional such as `&num;if &num;question(answer)'.
 `-A-' disables the standard assertions that normally describe the target machine.
  <item><bf>-Umacro</bf><label id="-Umacro" > Undefine macro macro. `-U' options are evaluated after all `-D'
 options, but before any `-include' and `-imac- ros' options.
  <item><bf>-dM</bf><label id="-dM" > Tell the preprocessor to output only a list of the mac- ro definitions
 that are in effect at the end of prepro- cessing. Used with the `-E' option.
  <item><bf>-dD</bf> <label id="-dD" >Tell the preprocessor to pass all macro definitions into the output,
 in their proper sequence in the rest of the output.
  <item><bf>-dN </bf><label id="-dN" >Like `-dD' except that the macro arguments and contents are omitted.
 Only `&num;define name' is included in the output.
  <item><bf>-S </bf><label id="-S" >Stop after the stage of compilation proper; do not as- semble. The output
 is an assembler code file for the input file specified.
  <item><bf>-Wa asmOption&lsqb;,asmOption&rsqb;</bf>... Pass the asmOption to the assembler
  <item><bf>-Wl linkOption&lsqb;,linkOption&rsqb;</bf> .. Pass the linkOption to the linker.
  <item><bf>--int-long-reent</bf> <label id="--int-long-rent" > 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.
  <item><bf>--cyclomatic </bf><label id="--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.
  <item><bf>--float-reent </bf><label id="--float-reent" > Floating point library is compiled as reentrant.See section
 Installation for more details.
  <item><bf>--out-fmt-ihx<label id="--out-fmt-ihx" > </bf>The linker output (final object code) is in Intel Hex format.
 (This is the default option).
  <item><bf>--out-fmt-s19 </bf><label id="--out-fmt-s19" >The linker output (final object code) is in Motorola S19
 format.
  <item><bf>--nooverlay</bf> <label id="--nooverlay" > The compiler will not overlay parameters and local variables
 of any function, see section Parameters and local variables for more details.
  <item><bf>--main-return</bf><label id="--main-return" > This option can be used when the code generated is called
 by a monitor program. The compiler will generate a 'ret' upon return from the
 'main' function. The default option is to lock up i.e. generate a 'ljmp .'
 .
  <item><bf>--no-peep</bf> <label id="--no-peep" > Disable peep-hole optimization.
  <item><bf>--peep-asm</bf> <label id="--peep-asm" > Pass the inline assembler code through the peep hole optimizer.
 Can cause unexpected changes to inline assembler code , please go through the
 peephole optimizer rules defnied in file 'SDCCpeeph.def' before using this
 option.
  <item><bf>--iram-size</bf><label id="--iram-size" > &lt;Value&gt; Causes the linker to check if the interal ram
 usage is within limits of the given value.
 </itemize></p>
 <p>The following options are provided for the purpose of retargetting and
 debugging the compiler . These provided a means to dump the intermediate code
 (iCode) generated by the compiler in human readable form at various stages
 of the compilation process. 
 </p>
 <p>
 <itemize>
  <item><bf>--dumpraw </bf><label id="--dumpraw" >. This option will cause the compiler to dump the intermediate
 code into a file of named &lt;source filename&gt;.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.
  <item><bf>--dumpgcse</bf>.<label id="--dumpgcse" > Will create a dump if iCode, after global subexpression elimination,
 into a file named &lt;source filename&gt;.dumpgcse.
  <item><bf>--dumpdeadcode </bf><label id="--dumpdeadcode" >.Will create a dump if iCode, after deadcode elimination,
 into a file named &lt;source filename&gt;.dumpdeadcode.
  <item><bf>--dumploop.</bf> <label id="--dumploop" >Will create a dump if iCode, after loop optimizations, into
 a file named &lt;source filename&gt;.dumploop.
  <item><bf>--dumprange.</bf> <label id="--dump-range" >Will create a dump if iCode, after live range analysis, into
 a file named &lt;source filename&gt;.dumprange.
  <item><bf>--dumpregassign. </bf><label id="--dumpregassign" >Will create a dump if iCode, after register assignment
 , into a file named &lt;source filename&gt;.dumprassgn.
  <item><bf>--dumpall. </bf><label id="--dumpall" >Will cause all the above mentioned dumps to be created.
 </itemize></p>
 <p>Note that the files created for the dump are appended to each time. So
 the files should be deleted manually , before each dump is created. 
 </p>
 <p>When reporting bugs, it will be very helpful if you could include these
 dumps along with the portion of the code that is causing the problem.
 </p>
 <sect>Language Extensions<label id="Language Extension" >
 <sect1>Storage Classes.<label id="Storage Classes" >
 <p>In addition to the ANSI storage classes SDCC allows the following 8051
 specific storage classes.
 </p>
 <sect2>xdata.<label id="xdata" >
 <p>Variables declared with this storage class will be placed in the extern
 RAM. This is the <bf>default</bf> storage class for Large Memory model .
 </p>
 <p>eg. xdata unsigned char xduc;
 </p>
 <sect2>data<label id="data" >
 <p>This is the <bf>default</bf> storage class for Small Memory model. Variables declared
 with this storage class will be allocated in the internal RAM.
 </p>
 <p>eg. data int iramdata;
 </p>
 <sect2>idata<label id="idata" >
 <p>Variables declared with this storage class will be allocated into the indirectly
 addressable portion of the internal ram of a 8051 .
 </p>
 <p>eg.idata int idi;
 </p>
 <sect2>bit<label id="bit" >
 <p>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.
 </p>
 <p>eg.bit iFlag;
 </p>
 <sect2>sfr / sbit<label id="sfr / sbit" >
 <p>Like the bit keyword, sfr / sbit signifies both a data-type and storage
 class, they are used to describe the special function registers and special
 bit variables of a 8051. 
 </p>
 <p>eg. 
 </p>
 <p>sfr at 0x80 P0; /* special function register P0 at location 0x80 */
 </p>
 <p>sbit at 0xd7 CY; /* CY (Carry Flag) */
 </p>
 <sect>Optimizations<label id="Optimizations" >
 <p>SDCC performs a a host of standard optimizations in addition to some MCU
 specific optimizations. 
 </p>
 <sect1>Sub-expression elimination<label id="Sub-expression Elimination" >
 <p>The compiler does local and global common subexpression elimination.
 </p>
 <p><tt>eg. </tt>
 </p>
 <p>
 <verb>i = x + y + 1; 
j = x + y;
 </verb></p>
 <p>will be translated to
 </p>
 <p>
 <verb>iTemp = x + y 
i = iTemp + 1 
j = iTemp
 </verb></p>
 <p>Some subexpressions are not as obvious as the above example.
 </p>
 <p>eg.
 </p>
 <p>
 <verb>a-&gt;b&lsqb;i&rsqb;.c = 10; 
a-&gt;b&lsqb;i&rsqb;.d = 11;
 </verb></p>
 <p>In this case the address arithmetic a-&gt;b&lsqb;i&rsqb; will be computed
 only once; the equivalent code in C would be.
 </p>
 <p>
 <verb>iTemp = a-&gt;b&lsqb;i&rsqb;; 
iTemp.c = 10; 
iTemp.d = 11;
 </verb></p>
 <p>The compiler will try to keep these temporary variables in registers.
 </p>
 <sect1>Dead-Code elimination.<label id="Dead-code elimination" >
 <p>eg.
 </p>
 <p>
 <verb>int global; 
void f () &lcub; 
  int i; 
  i = 1;    /* dead store */ 
  global
 = 1; /* dead store */ 
  global = 2; 
  return; 
  global = 3; /* unreachable
 */ 
&rcub;
 </verb></p>
 <p>will be changed to
 </p>
 <p>
 <verb>int global; void f () 
&lcub;     
 global = 2;     
 return; 
&rcub;
 </verb></p>
 <sect1>Copy-Propagation:<label id="Copy-Propagation" >
 <p>eg.
 </p>
 <p>
 <verb>int f() &lcub; 
   int i, j; 
   i = 10; 
   j = i; 
   return j; 
&rcub;
 </verb></p>
 <p>will be changed to 
 </p>
 <p>
 <verb>int f() &lcub; 
    int i,j; 
    i = 10; 
    j = 10; 
    return 10;
 
&rcub;
 </verb></p>
 <p>Note: the dead stores created by this copy propagation will be eliminated
 by dead-code elimination .
 </p>
 <sect1>Loop optimizations<label id="Loop Optimizations" >
 <p>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 (&num;pragma NOINDUCTION).
 </p>
 <sect2>Loop Invariant:<label id="Loop Invariant" >
 <p>eg
 </p>
 <p>
 <verb>for (i = 0 ; i &lt; 100 ; i ++) 
     f += k + l;
 </verb></p>
 <p>changed to
 </p>
 <p>
 <verb>itemp = k + l; 
for ( i = 0; i &lt; 100; i++ ) f += itemp;
 </verb></p>
 <p>As mentioned previously some loop invariants are not as apparent, all static
 address computations are also moved out of the loop.
 </p>
 <sect2>Strength reduction :<label id="Strength Reduction" >
 <p>This optimization substitutes an expression by a cheaper expression.
 </p>
 <p>eg.
 </p>
 <p>
 <verb>for (i=0;i &lt; 100; i++) ar&lsqb;i*5&rsqb; = i*3;
 </verb></p>
 <p>changed to
 </p>
 <p>
 <verb>itemp1 = 0; 
itemp2 = 0; 
for (i=0;i&lt; 100;i++) &lcub; 
     ar&lsqb;itemp1&rsqb;
 = itemp2; 
     itemp1 += 5; 
     itemp2 += 3; 
&rcub;
 </verb></p>
 <p>The more expensive multiplication is changed to a less expensive addition.
 </p>
 <sect2>Loop reversing:<label id="Loop reversing" >
 <p>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 compiers
 use data-dependency analysis to make this determination, SDCC uses a more simple
 minded analysis).
 </p>
 <p>
 <itemize>
  <item>The 'for' loop is of the form 
"for ( &lt;symbol&gt; = &lt;expression&gt;
 ; &lt;sym&gt; &lsqb;&lt; | &lt;=&rsqb; &lt;expression&gt; ; &lsqb;&lt;sym&gt;++
 | &lt;sym&gt; += 1&rsqb;)
       &lt;for body&gt;"
  <item>The &lt;for body&gt; does not contain "continue" or 'break".
  <item>All goto's are contained within the loop.
  <item>No function calls within the loop.
  <item>The loop control variable &lt;sym&gt; is not assigned any value within
 the loop
  <item>The loop control variable does NOT participate in any arithmetic operation
 within the loop.
  <item>There are NO switch statements in the loop.
 </itemize></p>
 <p>Note djnz instruction can be used for 8-bit values ONLY, therefore it is
 advantageous to declare loop control symbols as either 'char' or 'short', ofcourse
 this may not be possible on all situations.
 </p>
 <sect1>Algebraic simplifications:<label id="Algebraic Simplifications" >
 <p>SDCC does numerous algebraic simplifications, the following is a small
 sub-set of these optimizations.
 </p>
 <p>
 <verb>eg 
i = j + 0 ; /* changed to */ i = j; 
i /= 2; /* changed to */ i &gt;&gt;=
 1; 
i = j - j ; /* changed to */ i = 0; 
i = j / 1 ; /* changed to */ i = j;
 </verb></p>
 <p>Note the subexpressions given above are generally introduced by macro expansions
 or as a result of copy/constant propagation.
 </p>
 <sect1>'switch' statements.<label id="Switch Statement" >
 <p>SDCC changes switch statements to jump tables when the following conditions
 are true. 
 </p>
 <p>
 <itemize>
  <item>The case labels are in numerical sequence , the labels need not be in order,
 and the starting number need not be one or zero.
 </itemize></p>
 <p>eg 
 </p>
 <p>
 <verb>switch(i) &lcub;                         switch (i) &lcub; 
case 4:...
                          case 1: ... 
case 5:...                          case
 2: ... 
case 3:...                          case 3: ... 
case 6:...        
                  case 4: ... 
&rcub;                                   &rcub;
 </verb></p>
 <p>Both the above switch statements will be implemented using a jump-table.
 </p>
 <p>
 <itemize>
  <item>The number of case labels is at least three, since it takes two conditional
 statements to handle the boundary conditions.
  <item>The number of case labels is less than 84, since each label takes 3 bytes
 and a jump-table can be utmost 256 bytes long. 
 </itemize></p>
 <p>Switch statements which have gaps in the numeric sequence or those that
 have more that 84 case labels can be split into more than one switch statement
 for efficient code generation.
 </p>
 <p>eg
 </p>
 <p>
 <verb>switch (i) &lcub; 
case 1: ... 
case 2: ... 
case 3: ... 
case 4: ... 
case
 9: ... 
case 10: ... 
case 11: ... 
case 12: ... 
&rcub;
 </verb></p>
 <p>If the above switch statement is broken down into two switch statements
 </p>
 <p>
 <verb>switch (i) &lcub; 
case 1: ... 
case 2: ... 
case 3: ... 
case 4: ... 
&rcub;switch (i) &lcub; 
case 9: ... 
case 10: ... 
case 11: ... 
case 12:...
 
&rcub;
 </verb></p>
 <p>then both the switch statements will be implemented using jump-tables whereas
 the unmodified switch statement will not be .
 </p>
 <sect1>bit-shifting operations.<label id="bit shifting" >
 <p>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.
 </p>
 <p>eg.
 </p>
 <p>
 <verb>unsigned short i;... 
i&gt;&gt;= 4; 
..
 </verb></p>
 <p>generates the following code.
 </p>
 <p>
 <verb>mov a,_i 
swap a 
anl a,&num;0x0f 
mov _i,a
 </verb></p>
 <p>In general SDCC will never setup a loop if the shift count is known. Another
 example
 </p>
 <p>
 <verb>unsigned int i; 
... 
i &gt;&gt;= 9; 
...
 </verb></p>
 <p>will generate
 </p>
 <p>
 <verb>mov a,(_i + 1) 
mov (_i + 1),&num;0x00 
clr c 
rrc a 
mov _i,a
 </verb></p>
 <p>Note that SDCC stores numbers in little-endian format (i.e. lowest order
 first)
 </p>
 <sect2>Bit-rotation:<label id="bit rotation" >
 <p>A special case of the bit-shift operation is bit rotation, SDCC recognizes
 the following expression to be a left bit-rotation.
 </p>
 <p>
 <verb>unsigned char i; 
... 
i = ( ( i &lt;&lt; 1) | ( i &gt;&gt; 7)); 
...
 </verb></p>
 <p>will generate the following code.
 </p>
 <p>
 <verb>mov a,_i 
rl a 
mov _i,a
 </verb></p>
 <p>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
 &gt;&gt; 7) | (i &lt;&lt; 1)); /* left-bit rotation */
 </p>
 <sect1>Highest Order Bit.<label id="Highest Order Bit" >
 <p>It is frequently required to obtain the highest order bit of an integral
 type (int,long,short or char types). SDCC recognizes the following expression
 to yield the highest order bit and generates optimized code for it.
 </p>
 <p>
 <verb>eg 
unsigned int gint; 
foo () &lcub; 
unsigned char hob; 
   ... 
   hob
 = (gint &gt;&gt; 15) &amp; 1; 
   .. 
&rcub;
 </verb></p>
 <p>Will generate the following code.
 </p>
 <p>
 <verb>                             61 ;  hob.c 7 
   000A E5*01               
 62         mov  a,(_gint + 1) 
   000C 33                   63         rlc 
 a 
   000D E4                   64         clr  a 
   000E 13                  
 65         rrc  a 
   000F F5*02                66         mov  _foo_hob_1_1,a
 </verb></p>
 <p>Variations of this case however will NOT be recognized . It is a standard
 C expression , so I heartily recommend this 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.
 </p>
 <p>
 <verb>eg.xyz = gint + ((gint &gt;&gt; 15) &amp; 1);
 </verb></p>
 <p>will still be recognized.
 </p>
 <sect1>Peep-hole optimizer.<label id="Peep-Hole" >
 <p>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
 &lt;filename&gt; option. The rule language is best illustrated with examples.
 </p>
 <p>
 <verb>replace &lcub; 
mov &percnt;1,a 
mov a,&percnt;1 &rcub; by &lcub; mov &percnt;1,a
 &rcub;
 </verb></p>
 <p>The above rule will the following assembly sequence
 </p>
 <p>
 <verb>mov r1,a 
mov a,r1
 </verb></p>
 <p>to
 </p>
 <p>
 <verb>mov r1,a
 </verb></p>
 <p>Note: All occurrences of a '&percnt;n' ( pattern variable ) must denote
 the same string. With the above rule, the assembly sequence
 </p>
 <p>
 <verb>mov r1,a 
mov a,r2
 </verb></p>
 <p>will remain unmodified. Other special case optimizations may be added by
 the user (via --peep-file option), eg. some variants of the 8051 MCU allow
 only 'AJMP' and 'ACALL' , the following two rules will change all 'LJMP' &amp;
 'LCALL' to 'AJMP' &amp; 'ACALL'.
 </p>
 <p>
 <verb>replace &lcub; lcall &percnt;1 &rcub; by &lcub; acall &percnt;1 &rcub;
 
replace &lcub; ljmp &percnt;1 &rcub; by &lcub; ajmp &percnt;1 &rcub;
 </verb></p>
 <p>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.
 </p>
 <p>The syntax for a rule is as follows ,
 </p>
 <p>
 <verb>rule := replace &lsqb; restart &rsqb; '&lcub;' &lt;assembly sequence&gt;
 '&bsol;n' 
                            '&rcub;' by '&lcub;' '&bsol;n' 
   
                             &lt;assembly sequence&gt; '&bsol;n' 
         
                   '&rcub;' &lsqb;if &lt;functionName&gt; &rsqb; '&bsol;n' 
&lt;assembly
 sequence&gt; := assembly instruction (each instruction including labels must
 be on a separate line).   
 </verb></p>
 <p>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. A good example of this the following rule.
 </p>
 <p>
 <verb>replace restart &lcub; 
pop &percnt;1 
push &percnt;1 &rcub; by &lcub;
 
; nop 
&rcub;
 </verb></p>
 <p>Note that the replace pattern cannot be a blank, but can be a comment line.
 Without the 'restart' option only the inner most 'pop' 'push' pair would be
 eliminated. i.e.
 </p>
 <p>
 <verb>pop ar1 
pop ar2 
push ar2 
push ar1
 </verb></p>
 <p>would result in
 </p>
 <p>
 <verb>pop ar1 
; nop 
push ar1
 </verb></p>
 <p>with the 'restart' option the rule will be applied again to the resulting
 code and the all the 'pop' 'push' pairs will be eliminated to yield
 </p>
 <p>
 <verb>; nop 
; nop
 </verb></p>
 <p>A conditional function can be attached to a rule. Attaching rules are somewhat
 more involved, let me illustrate this with an example.
 </p>
 <p>
 <verb>replace &lcub; 
     ljmp &percnt;5 
&percnt;2:&rcub; by &lcub; 
     sjmp
 &percnt;5 
&percnt;2:&rcub; if labelInRange
 </verb></p>
 <p>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 '&percnt;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.
 I know this whole thing is a little kludgey , may be some day we will have
 some better means. If you are looking at this file, you will also see the default
 rules that are compiled into the compiler, you can your own rules in the default
 set there if you get tired of specifying the --peep-file option.
 </p>
 <sect>Pointers<label id="Pointers" >
 <p>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 also allows a _generic class of pointers which can be used to point
 to any of the memory spaces. 
 </p>
 <p>Pointer declaration examples.
 </p>
 <p>
 <verb>/* pointer physically in xternal 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;

/* the folowing is a generic pointer physically located
 in xdata space */
char * xdata p;
 </verb></p>
 <p>Well you get the idea. For compatibility with the previous version of the
 compiler, the following syntax for pointer declaration is also supported. Note
 the above examples will be portable to other commercially available compilers.
 </p>
 <p>
 <verb>unsigned char _xdata *ucxdp; /* pointer to data in external ram */ 
unsigned
 char _data  *ucdp ; /* pointer to data in internal ram */ 
unsigned char _code
  *uccp ; /* pointer to data in R/O code space */
unsigned char _idata *uccp;
  /* pointer to upper 128 bytes of ram */
 </verb></p>
 <p>All unqualified pointers are treated as 3 - byte '_generic' pointers. These
 type of pointers can also to be explicitly declared.
 </p>
 <p>
 <verb>unsigned char _generic *ucgp;
 </verb></p>
 <p>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. Pointers declared using a mixture of OLD/NEW style could
 have unpredictable results.
 </p>
 <sect>Parameters &amp; Local Variables<label id="Auto Variables" >
 <p>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
 Large model). They can be placed on the stack either by using the --stack-auto
 compiler option or by using the 'reentrant' keyword in the function declaration.
 </p>
 <p><tt>eg</tt>
 </p>
 <p>
 <verb>unsigned short foo( short i) reentrant &lcub; 
... 
&rcub;
 </verb></p>
 <p>Note that when the parameters &amp; local variables are declared in the
 internal/external ram the functions are non-reentrant. Since stack space on
 8051 is limited the 'reentrant' keyword or the --stack-auto option should be
 used sparingly. Note the reentrant keyword just means that the parameters &amp;
 local variables will be allocated to the stack, it DOES NOT mean that the function
 is register bank independent.
 </p>
 <p>When compiled with the default option (i.e. non-reentrant ), local variables
 can be assigned storage classes and absolute addresses. 
 </p>
 <p><tt>eg</tt>
 </p>
 <p>
 <verb>unsigned short foo() &lcub; 
   xdata unsigned short i; 
   bit bvar; 
 
  data at 0x31 unsiged short j; 
... 
&rcub;
 </verb></p>
 <p>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 the
 --stack-auto or when a function is declared as 'reentrant' local variables
 cannot be assigned storage classes or absolute addresses.
 </p>
 <p>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.
 </p>
 <sect1>Overlaying<label id="Overlaying" >
 <p>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 overplayed.
 </p>
 <p>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 &num;pragma NOOVERLAY if they are not reentrant
 Along the same lines the compiler does not do any processing with the inline
 assembler code so the compiler might incorrectly assign local variables and
 parameters of a function into the overlay segment if the only function call
 from a function is from inline assembler code, it is safe to use the &num;pragma
 NOOVERLAY for functions which call other functions using inline assembler code.
 </p>
 <p>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.
 </p>
 <p>eg.
 </p>
 <p>
 <verb>&num;pragma SAVE 
&num;pragma NOOVERLAY 
void set_error( unsigned short
 errcd) 
&lcub; 
    P3 = errcd; 
&rcub; 
&num;pragma RESTORE 
void some_isr
 () interrupt 2 using 1 
&lcub; 
    ... 
    set_error(10); 
    ... 
&rcub;
 </verb></p>
 <p>In the above example the parameter errcd for the function set_error would
 be assigned to the overlayable segment (if the &num;pragma NOOVERLAY was not
 present) , this could cause unpredictable runtime behavior. The pragma NOOVERLAY
 ensures that the parameters and local variables for the function are NOT overlayed.
 </p>
 <sect>critical Functions.<label id="Critical" >
 <p>A special keyword may be associated with a function declaring it as 'critical'.
 SDCC will generate code to disable all interrupts upon entry to a critical
 function and enable them back before returning . Note that nesting critical
 functions may cause unpredictable results.
 </p>
 <p>eg
 </p>
 <p>
 <verb>int foo () critical 
&lcub; 
... 
... 
&rcub;
 </verb></p>
 <p>The critical attribute maybe used with other attributes like reentrant.
 </p>
 <sect>Absolute addressing.<label id="Absolute Addressing" >
 <p>Data items can be assigned an absolute address with the at &lt;address&gt;
 keyword, in addition to a storage class.
 </p>
 <p>
 <verb>eg. xdata at 0x8000 unsigned char PORTA_8255 ;
 </verb></p>
 <p>In the above example the PORTA_8255 will be allocated to the location 0x8000
 of the external ram. 
 </p>
 <p>Note that is this feature is provided to give the programmer access to
 memory mapped devices attached to the controller. The compiler does not actually
 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
 (&lt;filename&gt;.rst) and (&lt;filename&gt;.map) are a good places to look
 for such overlaps.
 </p>
 <p>Absolute address can be specified for variables in all storage classes.
 </p>
 <p>
 <verb>eg.bit at 0x02 bvar;
 </verb></p>
 <p>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.
 </p>
 <sect>Interrupt Service Routines<label id="Interrupt Service Rouines" >
 <p>SDCC allows interrupt service routines to be coded in C, with some extended
 keywords.
 </p>
 <p>
 <verb>void timer_isr (void) interrupt 2 using 1 
&lcub; 
.. 
&rcub;
 </verb></p>
 <p>The number following the 'interrupt' keyword is the interrupt number this
 routine will service. The compiler will insert a call to this routine in the
 interrupt vector table for the interrupt number specified. The 'using' keyword
 is used to tell the compiler to use the specified register bank (8051 specific)
 when generating code for this function. Note that when some function is called
 from an interrupt service routine it should be preceded by a &num;pragma NOOVERLAY
 (if it is not reentrant) . A special note here, int (16 bit) and long (32 bit)
 integer division, multiplication &amp; modulus operations are implemented using
 external support routines developed in ANSI-C, 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 recompiled using the --stack-auto option
 and the source file will need to be compiled using the --int-long-rent compiler
 option.
 </p>
 <p>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 in
 the file that contains the function 'main'.
 </p>
 <p>Interrupt Numbers and the corresponding address &amp; descriptions for
 the Standard 8051 are listed below. SDCC will automatically adjust the interrupt
 vector table to the maximum interrupt number specified.
 </p>
 <p>
 <verb>Interrupt &num;         Description           Vector Address 
   0                External
 0            0x0003 
   1                Timer 0               0x000B 
   2
                External 1            0x0013 
   3                Timer 1               0x001B
 
   4                Serial                0x0023
 </verb></p>
 <p>If the interrupt service routine is defined without 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.
 </p>
 <p>If the interrupt service routine is defined to be using a specific register
 bank then only "a","b" &amp; "dptr" are save 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.
 </p>
 <p>Calling other functions from an interrupt service routine is not recommended
 avoid it if possible.
 </p>
 <sect>Startup Code<label id="Startup" >
 <p>The compiler inserts a jump to the C routine <bf>_sdcc__external__startup()
 </bf>at the start of the CODE area. This routine can be found in the file <bf>SDCCDIR/sdcc51lib/_startup.c</bf>
 , by default this routine returns 0, if this routine returns a non-zero value
 , the static &amp; global variable initialization will be skipped and the function
 main will be invoked, other wise static &amp; global variables will be initialized
 before the function main is invoked.
 </p>
 <sect>Inline assembler code.<label id="Inline" >
 <p>SDCC allows the use of in-line assembler with a few restriction as regards
 labels. All labels defined within inline assembler code HAS TO BE of the form
 nnnnn&dollar; where nnnn is a number less than 100 (which implies a limit of
 utmost 100 inline assembler labels per function). It is strongly recommended
 that each assembly instruction (including labels) be placed in a separate line
 ( as the example shows). When the <bf>--peep-asm</bf> command line option is used, the
 inline assembler code will be passed through the peephole optimizer, this might
 cause some unexpected changes in the inline assembler code, please go throught
 the peephole optimizer rules defined in file 'SDCCpeeph.def' carefully before
 using this option.
 </p>
 <p>
 <verb>eg_asm 
         mov b,&num;10 
00001&dollar;: 
         djnz b,00001&dollar;
 
_endasm ;
 </verb></p>
 <p>The inline assembler code can contain any valid code understood by the
 assembler (this includes any assembler directives and comment lines ) . The
 compiler does not do any validation of the code within the _asm ... _endasm;
 keyword pair. 
 </p>
 <p>Inline assembler code cannot reference any C-Labels however it can reference
 labels defined by the inline assembler.
 </p>
 <p>
 <verb>egfoo() &lcub; 
... /* some c code */ 
_asm 
     ; some assembler code 
 
   ljmp &dollar;0003 
_endasm ; 
... /* some more c code */ 
clabel:   /* inline
 assembler cannot reference this label */ 
_asm 
   &dollar;0003: ;label (can
 be reference by inline assembler only) 
_endasm ; 
... 
&rcub;
 </verb></p>
 <p>In other words inline assembly code can access labels defined in inline
 assembly. The same goes the other way, ie. labels defines in inline assembly
 CANNOT be accessed by C statements.
 </p>
 <sect>int (16 bit) and long (32 bit ) support.<label id="int and long" >
 <p>For signed &amp; 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. The following files contain the described routine, all of them
 can be found in the directory SDCCDIR/sdcc51lib
 </p>
 <p>
 <itemize>
  <item>_mulsint.c - signed 16 bit multiplication (calls _muluint)
  <item>_muluint.c - unsigned 16 bit multiplication
  <item>_divsint.c - signed 16 bit division (calls _divuint)
  <item>_divuint.c - unsigned 16 bit division.
  <item>_modsint.c - signed 16 bit modulus (call _moduint)
  <item>_moduint.c - unsigned 16 bit modulus.
  <item>_mulslong.c - signed 32 bit multiplication (calls _mululong)
  <item>_mululong.c - unsigned32 bit multiplication.
  <item>_divslong.c - signed 32 division (calls _divulong)
  <item>_divulong.c - unsigned 32 division.
  <item>_modslong.c - signed 32 bit modulus (calls _modulong).
  <item>_modulong.c - unsigned 32 bit modulus.
 </itemize></p>
 <p>All these routines are compiled as non-reentrant and small model. Since
 they are compiled as non-reentrant, interrupt service routines should not do
 any of the above operations, if this unavoidable then the above routines will
 need to ne compiled with the --stack-auto option, after which the source program
 will have to be compiled with --int-long-rent option.
 </p>
 <sect>Floating point support<label id="Float" >
 <p>SDCC supports IEEE (single precision 4bytes) floating point numbers.The
 floating point support routines are derived from gcc's floatlib.c and consists
 of the following routines. 
 </p>
 <p>
 <itemize>
  <item>_fsadd.c - add floating point numbers.
  <item>_fssub.c - subtract floating point numbers
  <item>_fsdiv.c - divide floating point numbers
  <item>_fsmul.c - multiply floating point numbers
  <item>_fs2uchar.c - convert floating point to unsigned char
  <item>_fs2char.c - convert floating point to signed char.
  <item>_fs2uint.c - convert floating point to unsigned int.
  <item>_fs2int.c - convert floating point to signed int.
  <item>_fs2ulong.c - convert floating point to unsigned long.
  <item>_fs2long.c - convert floating point to signed long.
  <item>_uchar2fs.c - convert unsigned char to floating point
  <item>_char2fs.c - convert char to floating point number
  <item>_uint2fs.c - convert unsigned int to floating point
  <item>_int2fs.c - convert int to floating point numbers
  <item>_ulong2fs.c - convert unsigned long to floating point number
  <item>_long2fs.c - convert long to floating point number.
 </itemize></p>
 <p>Note if all these routines are used simultaneously the data space might
 overflow. For serious floating point usage it is strongly recommended that
 the Large model be used (in which case the floating point routines mentioned
 above will need to recompiled with the --model-Large option)
 </p>
 <sect>Memory Models<label id="Memory Models" >
 <p>SDCC allows two memory models, modules compiled with different memory models
 should be combined together, the results would be unpredictable. The support
 routines supplied with the compiler are compiled in small-model by default,
 and will need to be recompiled using the large model if the large model is
 used. In general the use of the large model is discouraged.
 </p>
 <p>When the 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.
 </p>
 <p>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 strongly recommdended that the small model be used unless
 absolutely required.
 </p>
 <sect>Flat 24 bit addressing model.<label id="--model-flat24" >
 <p>This option 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.
 </p>
 <p>Note that the compiler does not generate any code to place the processor
 into this mode (it defaults to 8051 compatible mode). Boot loader or similar
 code must ensure that the processor is in 24 bit contiguous addressing mode
 before calling the SDCC startup code.
 </p>
 <p>Like the --model-large option, variables will by default be placed into
 the XDATA segment. However, a current limitation is that the compiler will
 spill variables into the DATA segment when it runs out of registers. This means
 that compiling complex code can rapidly fill up the DATA segment. This limitation
 is being worked on, and should be addressed in the next release of sdcc.
 </p>
 <p>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.
 </p>
 <p>--stack-10bit:
 </p>
 <p>This option generates code for the 10 bit stack mode of the Dallas DS80C390
 part. In this mode, the stack is located in the lower 1K of the internal RAM,
 which is mapped to 0x400000.
 </p>
 <p>With this option, sdcc will generate the proper addressing for stack variables.
 </p>
 <p>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 can 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.
 </p>
 <p>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.
 </p>
 <p>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).
 </p>
 <sect>Defines created by the compiler.<label id="Defines." >
 <p>The compiler creates the following &num;defines .
 </p>
 <p>
 <itemize>
  <item>SDCC - this Symbol is always defined.
  <item>SDCC_STACK_AUTO - this symbol is defined when --stack-auto option is used.
  <item>SDCC_MODEL_SMALL - when small model is used.
  <item>SDCC_MODEL_LARGE - when --model-large is used.
  <item>SDCC_USE_XSTACK - when --xstack option is used.
 </itemize></p>
 <sect>Pragmas<label id="Pragmaa" >
 <p>SDCC supports the following &num;pragma directives. This directives are
 applicable only at a function level.
 </p>
 <p>
 <itemize>
  <item><bf>SAVE</bf><label id="pragma save" > - this will save all the current options .
  <item><bf>RESTORE </bf><label id="pragma restore" >- will restore the saved options from the last save. Note that
 SAVES &amp; RESTOREs cannot be nested. SDCC uses the same buffer to save the
 options each time a SAVE is called.
  <item><bf>NOGCSE</bf><label id="pragma nogcse" > - will stop global subexpression elimination.
  <item><bf>NOINDUCTION</bf> <label id="pragma noinduction" >- will stop loop induction optimizations .
  <item><bf>NOJTBOUND</bf> <label id="pragma nojtbound" >- will not generate code for boundary value checking , when switch
 statements are turned into jump-tables.
  <item><bf>NOOVERLAY </bf><label id="pragma nooverlay" >- the compiler will not overlay the parameters and local variables
 of a function.
  <item><bf>NOLOOPREVERSE</bf> <label id="pragma noloopreverse" >- Will not do loop reversal optimization
  <item><bf>EXCLUDE NONE | &lcub;acc&lsqb;,b&lsqb;,dpl&lsqb;,dph&rsqb;&rsqb;&rsqb;</bf><label id="pragma exclude" >
 - The exclude pragma disables generation of pair of push/pop instruction in
 ISR function (using interrupt keyword). 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 "&num;pragma
 EXCLUDE none"
  <item><bf>CALLEE-SAVES function1&lsqb;,function2&lsqb;,function3...&rsqb;&rsqb;</bf><label id="pragma callee-saves" > -
 The compiler by default uses a caller saves convention for register saving
 across function calls, however this can cause unneccessary register pushing
 &amp; 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,
 extra code will be generated at the entry &amp; exit for these functions to
 save &amp; restore the registers used by these functions, this can SUBSTANTIALLY
 reduce code &amp; improve run time performance of the generated code. In future
 the compiler (with interprocedural analysis) will be able to determine the
 appropriate scheme to use for each function call. If --callee-saves<ref id="--callee-saves" name="" > command
 line option is used, the function names specified in &num;pragma CALLEE-SAVES
 is appended to the list of functions specified inthe command line.
 </itemize></p>
 <p>The pragma's are intended to be used to turn-off certain optimizations
 which might cause the compiler to generate extra stack / 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 &amp; optimizations for a given function; pragmas should
 be placed before and/or after a function, placing pragma's inside a function
 body could have unpredictable results.
 </p>
 <p>
 <verb>eg&num;pragma SAVE   /* save the current settings */ 
&num;pragma NOGCSE
 /* turnoff global subexpression elimination */ 
&num;pragma NOINDUCTION /*
 turn off induction optimizations */ 
int foo () 
&lcub; 
    ... 
    /* large
 code */ 
    ... 
&rcub; 
&num;pragma RESTORE /* turn the optimizations back
 on */
 </verb></p>
 <p>The compiler will generate a warning message when extra space is allocated.
 It is strongly recommended that the SAVE and RESTORE pragma's be used when
 changing options for a function.
 </p>
 <sect>Library routines.<label id="Library" >
 <p>The following library routines are provided for your convenience.
 </p>
 <p><bf>stdio.h </bf>- Contains the following functions printf &amp; sprintf these routines
 are developed by Martijn van Balen &lt;balen@natlab.research.philips.com&gt;.
 
 </p>
 <p>
 <verb>&percnt;&lsqb;flags&rsqb;&lsqb;width&rsqb;&lsqb;b|B|l|L&rsqb;type           flags: -        left justify output in specified field width
 
                 +        prefix output with +/- sign if output is signed
 type 
                 space    prefix output with a blank if it's a signed
 positive value 
          width:          specifies minimum number of characters
 outputted for numbers 
                          or strings. 
                         
 - For numbers, spaces are added on the left when needed. 
                           
 If width starts with a zero character, zeroes and used 
                           
 instead of spaces. 
                          - For strings, spaces are are
 added on the left or right (when 
                            flag '-' is used)
 when needed. 
                          
          b/B:            byte argument
 (used by d, u, o, x, X) 
          l/L:            long argument (used by d,
 u, o, x, X)
          type:  d        decimal number 
                 u       
 unsigned decimal number 
                 o        unsigned octal number 
                
 x        unsigned hexadecimal number (0-9, a-f) 
                 X       
 unsigned hexadecimal number (0-9, A-F) 
                 c        character
 
                 s        string (generic pointer) 
                 p       
 generic pointer (I:data/idata, C:code, X:xdata, P:paged) 
                
 f        float (still to be implemented)
 </verb></p>
 <p>Also contains a very simple version of printf (<bf>printf_small</bf>). This simplified
 version of printf supports only the following formats.
 </p>
 <p>
 <verb>format     output type     argument-type <bf>
</bf>&percnt;d         decimal      
 int 
&percnt;ld        decimal       long 
&percnt;hd        decimal       short/char
 
&percnt;x        hexadecimal    int 
&percnt;lx       hexadecimal    long
 
&percnt;hx       hexadecimal    short/char 
&percnt;o         octal         int
 
&percnt;lo        octal         long 
&percnt;ho        octal         short/char
 
&percnt;c        character      char/short 
&percnt;s        character     _generic
 pointer
 <p><tt>The routine is </tt><tt><bf>very stack intesive </bf>, --stack-after-data parameter should
 be used when using this routine, the routine also takes about 1K of code space
 .It also expects an external function named putchar(char ) to be present (this
 can be changed). When using the &percnt;s format the string / pointer should
 be cast to a generic pointer. eg.</tt>
 </p>
  <verb>printf_small("my str &percnt;s, my int &percnt;d&bsol;n",(char _generic *)mystr,myint);
  </verb>
 </verb>
 <p>
 <itemize>
  <item><bf>stdarg.h </bf>- contains definition for the following macros to be used for
 variable parameter list, note that a function can have a variable parameter
 list if and only if it is 'reentrant'
 <p>va_list, va_start, va_arg, va_end.
 </p>
  <item><bf>setjmp.h </bf>- contains defintion for ANSI<bf> setjmp </bf>&amp; <bf>longjmp</bf> routines. Note
 in this case setjmp &amp; longjmp can be used between functions executing within
 the same register bank, if long jmp is executed from a function that is using
 a different register bank from the function issuing the setjmp function, the
 results may be unpredictable. The jump buffer requires 3 bytes of data (the
 stack pointer &amp; a 16 byte return address), and can be placed in any address
 space.
  <item><bf>stdlib.h</bf> - contains the following functions.
 <p>atoi, atol.
 </p>
  <item><bf>string.h </bf>- contains the following functions.
 <p>strcpy, strncpy, strcat, strncat, strcmp, strncmp, strchr, strrchr, strspn,
 strcspn, strpbrk, strstr, strlen, strtok, memcpy, memcmp, memset.
 </p>
  <item><bf>ctype.h</bf> - contains the following routines.
 <p>iscntrl, isdigit, isgraph, islower, isupper, isprint, ispunct, isspace,
 isxdigit, isalnum, isalpha.
 </p>
  <item><bf>malloc.h</bf> - The malloc routines are developed by Dmitry S. Obukhov (dso@usa.net).
 These routines will allocate memory from the external ram. Here is a description
 on how to use them (as described by the author).
  <verb>//Example: 
     //     &num;define DYNAMIC_MEMORY_SIZE 0x2000 
     //    
 ..... 
     //     unsigned char xdata dynamic_memory_pool&lsqb;DYNAMIC_MEMORY_SIZE&rsqb;;
 
     //     unsigned char xdata * current_buffer; 
     //     ..... 
    
 //     void main(void) 
     //     &lcub; 
     //         ... 
     //        
 init_dynamic_memory(dynamic_memory_pool,DYNAMIC_MEMORY_SIZE); 
     //        
 //Now it's possible to use malloc. 
     //         ... 
     //         current_buffer
 = malloc(0x100); 
     //
  </verb>
  <item><bf>serial.h</bf> - Serial IO routines are also developed by Dmitry S. Obukhov (dso@usa.net).
 These routines are interrupt driven with a 256 byte circular buffer, they also
 expect external ram to be present. Please see documentation in file SDCCDIR/sdcc51lib/serial.c
 . Note the header file "serial.h" MUST be included in the file containing the
 'main' function.
  <item><bf>ser.h </bf>- Alternate serial routine provided by Wolfgang Esslinger &lt;wolfgang@WiredMinds.com&gt;
 these routines are more compact and faster. Please see documentation in file
 SDCCDIR/sdcc51lib/ser.c
  <item><bf>ser_ir.h </bf>- Another alternate set of serial routines provided by Josef Wolf
 &lt;jw@raven.inka.de&gt; , these routines do not use the external ram.
  <item><bf>reg51.h</bf> - contains register definitions for a standard 8051
  <item><bf>reg552.h </bf>- contains register definitions for 80C552.
  <item><bf>float.h</bf> - contains min, max and other floating point related stuff.
 </itemize></p>
 <p>All library routines are compiled as --model-small , they are all non-reentrant,
 if you plan to use the large model or want to make these routines reentrant,
 then they will have to be recompiled with the appropriate compiler option.
 </p>
 <p>Have not had time to do the more involved routines like printf, will get
 to them shortly.
 </p>
 <sect>Interfacing with assembly routines.<label id="Interface_asm" >
 <sect1>Global registers used for parameter passing.
 <p>By default the compiler uses the global registers "DPL,DPH,B,ACC" to pass
 the first parameter to a routine, the second parameter onwards is either allocated
 on the stack (for reentrant routines or --stack-auto is used) or in the internal
 / external ram (depending on the memory model). 
 </p>
 <sect2>Assembler routine non-reentrant
 <p>In the following example the function<bf> cfunc</bf> calls an assembler routine
 <bf>asm_func</bf>, which takes two parameters.
 </p>
 <p>extern int asm_func( unsigned short, unsigned short);
 </p>
 <p>
 <verb> 
int c_func (unsigned short i, unsigned short j) 
&lcub; 
        return
 asm_func(i,j); 
&rcub; 
int main() 
&lcub; 
   return c_func(10,9); 
&rcub;
 </verb></p>
 <p>The corresponding assembler function is:-
 </p>
 <p>
 <verb>        .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     dpl,&num;0x00 
        ret
 </verb></p>
 <p>Note here that the return values are placed in 'dpl' - One byte return
 value, 'dpl' LSB &amp; 'dph' MSB for two byte values. 'dpl', 'dph' and 'b'
 for three byte values (generic pointers) and 'dpl','dph','b' &amp; 'acc' for
 four byte values.
 </p>
 <p>The parameter naming convention is <bf>_&lt;function_name&gt;_PARM_&lt;n&gt;,</bf>
 where n is the parameter number starting from 1, and counting from the left.
 The first parameter is passed in "dpl" for One bye parameter, "dptr" if two bytes,
 "b,dptr" for three bytes and "acc,b,dptr" for four bytes, the <tt></tt><tt><bf>varaible name for
 the second parameter will be _&lt;function_name&gt;_PARM_2.</bf></tt>
 </p>
 <p>Assemble the assembler routine with the following command.
 </p>
 <p>
 <verb>asx8051 -losg asmfunc.asm
 </verb></p>
 <p>Then compile and link the assembler routine to the C source file with the
 following command,
 </p>
 <p>
 <verb>sdcc cfunc.c asmfunc.rel
 </verb></p>
 <sect2>Assembler routine is reentrant
 <p>In this case the second parameter onwards will be passed on the stack ,
 the parameters are pushed from right to left i.e. after the call the left most
 parameter will be on the top of the stack. Here is an example.
 </p>
 <p>extern int asm_func( unsigned short, unsigned short);
 </p>
 <p>
 <verb> int c_func (unsigned short i, unsigned short j) reentrant 
&lcub; 
       
 return asm_func(i,j); 
&rcub; 
int main() 
&lcub; 
   return c_func(10,9);
 
&rcub;
 </verb></p>
 <p>The corresponding assembler routine is.
 </p>
 <p>
 <verb>        .globl _asm_func 
_asm_func: 
        push  _bp 
        mov  _bp,sp
 
        mov  r2,dpl
        mov  a,_bp 
        clr  c 
        add  a,&num;0xfd
 
        mov  r0,a 
        add  a,&num;0xfc
        mov  r1,a 
        mov 
 a,@r0 
        add  a,r2
        mov  dpl,a 
        mov  dph,&num;0x00 
       
 mov  sp,_bp 
        pop  _bp 
        ret
 </verb></p>
 <p>The compiling and linking procedure remains the same, however note the
 extra entry &amp; 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.
 </p>
 <sect1>With --noregparms option.
 <p>When the source is compiled with --noregparms option , space is allocated
 for each of the parameters passed to a routine.
 </p>
 <sect2>Assembler routine non-reentrant.
 <p>In the following example the function<bf> cfunc</bf> calls an assembler routine
 <bf>asm_func</bf>, which takes two parameters.
 </p>
 <p>
 <verb>extern int asm_func( unsigned short, unsigned short); 
int c_func (unsigned short i, unsigned short j) 
&lcub; 
        return
 asm_func(i,j); 
&rcub; 
int main() 
&lcub; 
   return c_func(10,9); 
&rcub;
 </verb></p>
 <p>The corresponding assembler function is:-
 </p>
 <p>
 <verb>        .globl _asm_func_PARM_1 
        .globl _asm_func_PARM_2 
       
 .globl _asm_func 
        .area OSEG 
_asm_func_PARM_1:       .ds     1 
_asm_func_PARM_2:      
 .ds      1 
        .area CSEG 
_asm_func: 
        mov     a,_asm_func_PARM_1
 
        add     a,_asm_func_PARM_2 
        mov     dpl,a 
        mov    
 dpl,&num;0x00 
        ret
 </verb></p>
 <p>Note here that the return values are placed in 'dpl' - One byte return
 value, 'dpl' LSB &amp; 'dph' MSB for two byte values. 'dpl', 'dph' and 'b'
 for three byte values (generic pointers) and 'dpl','dph','b' &amp; 'acc' for
 four byte values.
 </p>
 <p>The parameter naming convention is <bf>_&lt;function_name&gt;_PARM_&lt;n&gt;,</bf>
 where n is the parameter number starting from 1, and counting from the left.
 i.e. the <tt></tt><tt><bf>left-most parameter name will be _&lt;function_name&gt;_PARM_1.
</bf></tt>
 </p>
 <p>Assemble the assembler routine with the following command.
 </p>
 <p>
 <verb>asx8051 -losg asmfunc.asm
 </verb></p>
 <p>Then compile and link the assembler routine to the C source file with the
 following command,
 </p>
 <p>
 <verb>sdcc cfunc.c asmfunc.rel
 </verb></p>
 <sect2>Assembler routine is reentrant.
 <p>In this case the parameters will be passed on the stack , the parameters
 are pushed from right to left i.e. after the call the left most parameter will
 be on the top of the stack. Here is an example.
 </p>
 <p>extern int asm_func( unsigned short, unsigned short);
 </p>
 <p>
 <verb> int c_func (unsigned short i, unsigned short j) reentrant 
&lcub; 
       
 return asm_func(i,j); 
&rcub; 
int main() 
&lcub; 
   return c_func(10,9);
 
&rcub;
 </verb></p>
 <p>The corresponding assembler routine is.
 </p>
 <p>
 <verb>        .globl _asm_func 
_asm_func: 
        push  _bp 
        mov  _bp,sp
 
        mov  a,_bp 
        clr  c 
        add  a,&num;0xfd 
        mov 
 r0,a 
        mov  a,_bp 
        clr  c 
        add  a,&num;0xfc 
       
 mov  r1,a 
        mov  a,@r0 
        add  a,@r1 
        mov  dpl,a 
       
 mov  dph,&num;0x00 
        mov  sp,_bp 
        pop  _bp 
        ret
 </verb></p>
 <p>The compiling and linking procedure remains the same, however note the
 extra entry &amp; 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.
 </p>
 <sect>External Stack.<label id="xstack" >
 <p>The external stack is located at the start of the external ram segment
 , and is 256 bytes in size. 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).
 </p>
 <p>The compiler outputs the higher order address byte of the external ram
 segment into PORT P2, therefore when using the External Stack option, this
 port MAY NOT be used by the application program.
 </p>
 <sect>ANSI-Compliance.<label id="ANSI_Compliance" >
 <p>Deviations from the compliancy.
 </p>
 <p>
 <enum>
  <item>functions are not always reentrant.
  <item>structures 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.
  <verb>eg
  </verb>
 </enum>
 <p>
 <verb>struct s &lcub; ... &rcub;; 
struct s s1, s2; 
foo() 
&lcub; 
... 
s1 =
 s2 ; /* is invalid in SDCC although allowed in ANSI */ 
... 
&rcub;struct s foo1 (struct s parms) /* is invalid in SDCC although allowed in
 ANSI */ 
&lcub; 
struct s rets; 
... 
return rets;/* is invalid in SDCC although
 allowed in ANSI */ 
&rcub;
 </verb>
 <p>
 <enum>
  <item>'long long' (64 bit integers) not supported.
  <item>'double' precision floating point not supported.
  <item>integral promotions are suppressed. What does this mean ? The compiler
 will not implicitly promote an integer expression to a higher order integer,
 exception is an assignment or parameter passing. 
  <item>No support for setjmp and longjmp (for now).
  <item>Old K&amp;R style function declarations are NOT allowed.
 </enum>
 <p>
 <verb>foo( i,j) /* this old style of function declarations */ 
int i,j; /* are
 valid in ANSI .. not valid in SDCC */ 
&lcub; 
... 
&rcub;
 </verb>
 <p>
 <enum>
  <item>functions declared as pointers must be dereferenced during the call.
  <verb>int (*foo)();
  </verb>
 </enum>
 <p>
 <verb>   ... 
   /* has to be called like this */ 
   (*foo)();/* ansi standard
 allows calls to be made like 'foo()' */
 </verb></p>
 <sect>Cyclomatic Complexity<label id="Cyclomatic" >
 <p>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.
 </p>
 <p>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.
 </p>
 <p>
 <verb>complexity = (number of edges in control flow graph) - 
             (number
 of nodes in control flow graph) + 2;
 </verb></p>
 <p>Having said that the industry standard is 10, you should be aware that
 in some cases it 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.
 </p>
 <sect>TIPS<label id="Tips" >
 <p>Here are a few guide-lines that will help the compiler generate more efficient
 code, some of the tips are specific to this compiler others are generally good
 programming practice.
 </p>
 <p>
 <itemize>
  <item>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 a 'short' or
 'char' instead of an 'int'.
  <item>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.
  <item>NEVER jump into a LOOP.
  <item>Declare the variables to be local whenever possible, especially loop control
 variables (induction).
  <item>Since the compiler does not do implicit integral promotion, the programmer
 should do an explicit cast when integral promotion is required.
  <item>Reducing the size of division , multiplication &amp; modulus operations
 can reduce code size substantially. Take the following code for example.
  <verb>foobar( unsigned int p1, unsigned char ch)
&lcub;
    unsigned char ch1
 = p1 &percnt; ch ;
    ....    
&rcub;
  </verb>
 <p>For the modulus operation the variable ch will be promoted to unsigned
 int first then the modulus operation will be performed (this will lead to a
 call to a support routine). If the code is changed to 
 </p>
  <verb>foobar( unsigned int p1, unsigned char ch)
&lcub;
    unsigned char ch1
 = (unsigned char)p1 &percnt; ch ;
    ....    
&rcub;
  </verb>
 <p>It would substantially reduce the code generated (future versions of the
 compiler will be smart enough to detect such optimization oppurtunities).
 </p>
 </itemize></p>
 <p><bf>Notes from an USER ( Trefor@magera.freeserve.co.uk )</bf>
 </p>
 <p>The 8051 family of micro controller have a minimum of 128 bytes of internal
 memory which is structured as follows
 </p>
 <p>- Bytes 00-1F - 32 bytes to hold up to 4 banks of the registers R7 to R7
 
 </p>
 <p>- Bytes 20-2F - 16 bytes to hold 128 bit variables and 
 </p>
 <p>- Bytes 30-7F - 60 bytes for general purpose use.
 </p>
 <p>Normally the SDCC compiler will only utilise the first bank of registers,
 but it is possible to specify that other banks of registers should be used
 in interrupt routines. By default, the compiler will place the stack after
 the last bank of used registers, i.e. if the first 2 banks of registers are
 used, it will position the base of the internal stack at address 16 (0X10).
 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 60 bytes for general
 purpose use.
 </p>
 <p>By default, the compiler uses the 60 general purpose bytes to hold &dquot;near
 data&dquot;. The compiler/optimiser may also declare some Local Variables in
 this area to hold local data. 
 </p>
 <p>If any of the 128 bit variables are used, or near data is being used then
 care needs to be taken to ensure that the stack does not grow so much that
 it starts to over write either your bit variables or &dquot;near data&dquot;.
 There is no runtime checking to prevent this from happening.
 </p>
 <p>The amount of stack being used is affected by the use of the &dquot;internal
 stack&dquot; to save registers before a subroutine call is made, - --stack-auto
 will declare parameters and local variables on the stack - the number of nested
 subroutines.
 </p>
 <p>If you detect that the stack is over writing you data, then the following
 can be done. --xstack will cause an external stack to be used for saving registers
 and (if --stack-auto is being used) storing parameters and local variables.
 However this will produce more and code which will be slower to execute. 
 </p>
 <p>--stack-loc will allow you specify the start of the stack, i.e. you could
 start it after any data in the general purpose area. However this may waste
 the memory not used by the register banks and if the size of the &dquot;near
 data&dquot; increases, it may creep into the bottom of the stack.
 </p>
 <p>--stack-after-data, similar to the --stack-loc, but it automatically places
 the stack after the end of the &dquot;near data&dquot;. Again this could waste
 any spare register space.
 </p>
 <p>--data-loc allows you to specify the start address of the near data. This
 could be used to move the &dquot;near data&dquot; further away from the stack
 giving it more room to grow. This will only work if no bit variables are being
 used and the stack can grow to use the bit variable space.
 </p>
 <p>Conclusion.
 </p>
 <p>If you find that the stack is over writing your bit variables or &dquot;near
 data&dquot; then the approach which best utilised the internal memory is to
 position the &dquot;near data&dquot; after the last bank of used registers
 or, if you use bit variables, after the last bit variable by using the --data-loc,
 e.g. if two register banks are being used and no data variables, --data-loc
 16, and - use the --stack-after-data option.
 </p>
 <p>If bit variables are being used, another method would be to try and squeeze
 the data area in the unused register banks if it will fit, and start the stack
 after the last bit variable.
 </p>
 <sect>Retargetting for other MCUs.<label id="Retargetting" >
 <p>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.
 </p>
 <p>
 <enum>
  <item>Parsing the source and building the annotated parse tree. This phase is
 largely MCU independent (except for the language extensions). Syntax &amp;
 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.
  <item>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.
  <item>This phase does the bulk of the standard optimizations and is also MCU
 independent. This phase can be broken down into several sub-phases.
  <itemize>
   <item>Break down intermediate code (iCode) into basic blocks.
   <item>Do control flow &amp; data flow analysis on the basic blocks.
   <item>Do local common subexpression elimination, then global subexpression elimination
   <item>dead code elimination
   <item>loop optimizations
   <item>if loop optimizations caused any changes then do 'global subexpression
 elimination' and 'dead code elimination' again.
  </itemize>
  <item>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.
  <item>Phase five is register allocation. There are two parts to this process
 .
  <enum>
   <item>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.
   <item>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.
  </enum>
  <item>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.
  <item>As mentioned in the optimization section the peep-hole optimizer is rule
 based system, which can reprogrammed for other MCUs.
 </enum></p>
 <sect>Reporting Bugs<label id="Bugs" >
 <p>Shoot of an email to 'sandeep.dutta@usa.net', as a matter of principle
 I always reply to all email's sent to me. Bugs will be fixed ASAP. When reporting
 a bug , it is useful to include a small snippet of code that is causing the
 problem, if possible compile your program with the --dumpall option and send
 the dump files along with the bug report.
 </p>
 <sect>SDCDB - Source level debugger.
 <p>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
 of the compiler see Installation <ref id="Installation" name="" > 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.
 </p>
 <sect1>Compiling for debugging.
 <p>The --debug option must be specified for all files for which debug information
 is to be generated. The complier generates a .cdb file for each of these files.
 The linker updates the .cdb file with the address information. This .cdb is
 used by the debugger .
 </p>
 <sect1>How the debugger works.
 <p>When the --debug option is specified the compiler generates extra symbol
 information some of which are put into the the assembler source and some are
 put into the .cdb file, the linker updates the .cdb file with the address information
 for the symbols. The debugger reads the symbolic information generated by the
 compiler &amp; 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 .
 </p>
 <sect1>Starting the debugger.
 <p>The debugger can be started using the following command line. (Assume the
 file you are debugging has
 </p>
 <p>the file name foo).
 </p>
 <p>
 <verb>&gt;sdcdb foo
 </verb></p>
 <p>The debugger will look for the following files.
 </p>
 <p>
 <enum>
  <item>foo.c - the source file.
  <item>foo.cdb - the debugger symbol information file.
  <item>foo.ihx - the intel hex format object file.
 </enum></p>
 <sect1>Command line options.
 <p>
 <itemize>
  <item>--directory=&lt;source file directory&gt; this option can used to specify
 the directory search list. The debugger will look into the directory list specified
 for source , cdb &amp; 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. 
  <item>-cd &lt;directory&gt; - change to the &lt;directory&gt;.
  <item>-fullname - used by GUI front ends.
  <item>-cpu &lt;cpu-type&gt; - this argument is passed to the simulator please
 see the simulator docs for details.
  <item>-X &lt;Clock frequency &gt; this options is passed to the simulator please
 see simulator docs for details.
  <item>-s &lt;serial port file&gt; passed to simulator see simulator docs for
 details.
  <item>-S &lt;serial in,out&gt; passed to simulator see simulator docs for details.
 </itemize></p>
 <sect1>Debugger Commands.
 <p>As mention earlier the command interface for the debugger has been deliberately
 kept as close the GNU debugger gdb , as possible, this will help int integration
 with existing graphical user interfaces (like ddd, xxgdb or xemacs) existing
 for the GNU debugger.
 </p>
 <sect2>break &lsqb;line | file:line | function | file:function&rsqb;
 <p>Set breakpoint at specified line or function.
 </p>
 <p>
 <verb>sdcdb&gt;break 100 
sdcdb&gt;break foo.c:100
sdcdb&gt;break funcfoo
sdcdb&gt;break
 foo.c:funcfoo
 </verb></p>
 <sect2>clear &lsqb;line | file:line | function | file:function &rsqb;
 <p>Clear breakpoint at specified line or function.
 </p>
 <p>
 <verb>sdcdb&gt;clear 100
sdcdb&gt;clear foo.c:100
sdcdb&gt;clear funcfoo
sdcdb&gt;clear
 foo.c:funcfoo
 </verb></p>
 <sect2>continue
 <p>Continue program being debugged, after breakpoint.
 </p>
 <sect2>finish
 <p>Execute till the end of the current function.
 </p>
 <sect2>delete &lsqb;n&rsqb;
 <p>Delete breakpoint number 'n'. If used without any option clear ALL user
 defined break points.
 </p>
 <sect2>info &lsqb;break | stack | frame | registers &rsqb;
 <p>
 <itemize>
  <item>info break - list all breakpoints
  <item>info stack - show the function call stack.
  <item>info frame - show information about the current execution frame.
  <item>info registers - show content of all registers.
 </itemize></p>
 <sect2>step
 <p>Step program until it reaches a different source line.
 </p>
 <sect2>next
 <p>Step program, proceeding through subroutine calls.
 </p>
 <sect2>run
 <p>Start debugged program.
 </p>
 <sect2>ptype variable 
 <p>Print type information of the variable.
 </p>
 <sect2>print variable
 <p>print value of variable.
 </p>
 <sect2>file filename
 <p>load the given file name. Note this is an alternate method of loading file
 for debugging.
 </p>
 <sect2>frame
 <p>print information about current frame.
 </p>
 <sect2>set srcmode
 <p>Toggle between C source &amp; assembly source.
 </p>
 <sect2>! simulator command
 <p>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.
 </p>
 <sect2>quit.
 <p>&dquot;Watch me now. Iam going Down. My name is Bobby Brown&dquot;
 </p>
 <sect1>Interfacing with XEmacs.
 <p>Two files are (in emacs lisp) are provided for the interfacing with XEmacs,
 sdcdb.el and sdcdbsrc.el. These two files can be found in the &dollar;(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) &lsqb; .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 &lsqb;&dollar;(prefix)/bin&rsqb;, 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. 
 </p>
 <p>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.
 </p>
 <p>
 <itemize>
  <item>sdcdbsrc-cpu-type '51
  <item>sdcdbsrc-frequency '11059200
  <item>sdcdbsrc-serial nil
 </itemize></p>
 <p>The following is a list of key mapping for the debugger interface.
 </p>
 <p>
 <verb> 
;; 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 
;; 

 </verb></p>
 <sect>Conclusion<label id="Conclusion" >
 <p>SDCC is a large project , the compiler alone (without the Assembler Package
 , Preprocessor &amp; garbage collector) is about 40,000 lines of code (blank
 stripped). As with any project of this size there are bound to be bugs, I am
 more than willing to work to fix these bugs , of course all the source code
 is included with the package. 
 </p>
 <p>Where does it go from here ? I am planning to target the Atmel AVR 8-bit
 MCUs which seems to have a lot of users. I am also planning to include an alias
 analysis system with this compiler (it does not currently have one).
 </p>
 <sect>Acknowledgments<label id="Acknowledgements" >
 <p>Alan Baldwin (baldwin@shop-pdp.kent.edu) - Initial version of ASXXXX &amp;
 ASLINK. 
 </p>
 <p>John Hartman (jhartman@compuserve.com) - Porting ASXXX &amp; ASLINK for
 8051
 </p>
 <p>Dmitry S. Obukhov (dso@usa.net) - malloc &amp; serial i/o routines. 
 </p>
 <p>Daniel Drotos &lt;drdani@mazsola.iit.uni-miskolc.hu&gt; - for his Freeware
 simulator
 </p>
 <p>Jans J Boehm(boehm@sgi.com) and Alan J Demers - Conservative garbage collector
 for C &amp; C++.
 </p>
 <p>Malini Dutta(malini_dutta@hotmail.com) - my wife for her patience and support.
 </p>
 <p>Unknown - for the GNU C - preprocessor.
 </p>
 <sect>Appendix A: The Z80 and gbz80 port
 <p>2.2.0 can target both the Zilog Z80 and the Nintendo Gameboy's Z80-like
 gbz80. The port is incomplete - long support is incomplete (mul, div and mod
 are unimplimented), and both float and bitfield support is missing, but apart
 from that the code generated is correct.
 </p>
 <p>As always, the code is the authoritave 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 is used as a temporary register, and BC
 and DE are available for holding varibles. IY is currently unusued. Return
 values are stored in HL. One bad side effect of using IX as the base pointer
 is that a functions stack frame is limited to 127 bytes - this will be fixed
 in a later version.bc
 </p>
 <p>9
 </p>
 <p>
 </p>


 </linuxdoc>