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283 lines
8.7 KiB
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283 lines
8.7 KiB
Plaintext
<!doctype linuxdoc system>
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<article>
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<title>Commodore 610 specific information for cc65
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<author>Ullrich von Bassewitz, <htmlurl url="mailto:uz@cc65.org" name="uz@cc65.org">
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<date>2003-12-16
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<abstract>
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An overview over the Commodore 610 runtime system as it is implemented for the
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cc65 C compiler.
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</abstract>
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<!-- Table of contents -->
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<toc>
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<!-- Begin the document -->
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<sect>Overview<p>
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This file contains an overview of the CBM 610 runtime system as it comes with
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the cc65 C compiler. It describes the memory layout, CBM 610 specific header
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files, available drivers, and any pitfalls specific to that platform.
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Please note that CBM 610 specific functions are just mentioned here, they are
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described in detail in the separate <htmlurl url="funcref.html" name="function
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reference">. Even functions marked as "platform dependent" may be available on
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more than one platform. Please see the function reference for more
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information.
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In addition to the Commodore 610 (named B40 in the U.S.), several other
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machines are supported by this cc65 target, since they have identical
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hardware: The Commodore 620 and 630 (more memory, additional coprocessor
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card), and the Commodore 710, 720 and 730 (same hardware in another case with
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a builtin monitor).
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<sect>Binary format<p>
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The standard binary output format generated by the linker for the CBM610
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target is a machine language program with a short BASIC stub. This means that
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a program can be loaded as BASIC program and started with RUN. It is of course
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possible to change this behaviour by using a modified startup file and linker
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config.
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<sect>Memory layout<p>
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cc65 generated programs for the Commodore 610 run in bank 1, the memory bank
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reserved for BASIC programs. Since there are no ROMs in this memory bank, the
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program has almost full 64K for its own. A disadvantage is that kernal
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subroutines cannot be called (at least not in a fast and effective manner), so
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the runtime has replace kernal functionality.
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The default memory configuration for the CBM 610 allocates all memory between
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$0002 and $FFF0 in bank 1 for the compiled program. Some space
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in low memory is lost, because a separate hardware stack is set up in page 1,
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and the kernal replacement functions need some more memory locations. A few
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more bytes are lost in high memory, because the runtime sets up a CBM
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compatible jump table at $FF81. The main startup code is located at
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$0400, so about 63K of the complete bank are actually usable for
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applications.
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<bf>Note:</bf> The zero page from $02 to $5F is free to use for
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applications!
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Special locations:
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<descrip>
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<tag/Stack/
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The C runtime stack is located at $FF81 and growing downwards.
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<tag/Heap/
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The C heap is located at the end of the program and grows towards the C
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runtime stack.
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</descrip><p>
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<sect>Platform specific header files<p>
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Programs containing CBM 610 specific code may use the <tt/cbm610.h/ or
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<tt/cbm.h/ header files. Using the later may be an option when writing code
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for more than one CBM platform, since it includes <tt/cbm610.h/ and declares
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several functions common to all CBM platforms.
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Please note that because of <ref id="limitations" name="current limitations">
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of the runtime library for the platform, several standard C and CBM functions
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are not available.
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<sect1>CBM 610 specific functions<p>
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The functions listed below are special for the CBM 610. See the <htmlurl
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url="funcref.html" name="function reference"> for declaration and usage.
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<itemize>
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<item>peekbsys
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<item>peewsys
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<item>pokebsys
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<item>pokewsys
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</itemize>
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<sect1>CBM specific functions<p>
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Some functions are available for all (or at least most) of the Commodore
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machines. See the <htmlurl url="funcref.html" name="function reference"> for
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declaration and usage.
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<sect1>Hardware access<p>
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The following pseudo variables declared in the <tt/cbm610.h/ header file do
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allow access to hardware located in the address space. Some variables are
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structures, accessing the struct fields will access the chip registers.
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<bf>Note:</bf> All I/O chips are located in the system bank (bank 15) and can
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therefore not be accessed like on other platforms. Please use one of the
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<tt/peekbsys/, <tt/peewsys/, <tt/pokebsys/ and <tt/pokewsys/ functions to
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access the I/O chips. Direct reads and writes to the structures named below
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will <em>not</em> work!
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<descrip>
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<tag><tt/CRTC/</tag>
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The <tt/CRTC/ structure allows access to the CRTC (the video controller).
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See the <tt/_6545.h/ header file located in the include directory for the
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declaration of the structure.
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<tag><tt/SID/</tag> The <tt/SID/ structure allows access to the SID (the
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sound interface device). See the <tt/_sid.h/ header file located in the
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include directory for the declaration of the structure.
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<tag><tt/ACIA/</tag>
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Access to the ACIA (the RS232 chip) is available via the <tt/ACIA/ variable.
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See the <tt/_6551.h/ header file located in the include directory for the
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declaration of the structure.
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<tag><tt/CIA/</tag>
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Access to the CIA chip is available via the <tt/CIA/ variable. See the
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<tt/_6526.h/ header file located in the include directory for the
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declaration of the structure.
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<tag><tt/TPI1, TPI2/</tag>
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The two 6525 triport chips may be accessed by using this variable. See the
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<tt/_6525.h/ header file located in the include directory for the
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declaration of the structure.
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</descrip><p>
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<sect>Loadable drivers<p>
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<bf>Note:</bf> Since the CBM 610 doesn't have working disk I/O (see <ref
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id="limitations" name="section "Limitations"">), the available
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drivers cannot be loaded at runtime (so the term "loadable drivers" is
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somewhat misleading). Instead, the drivers have to be converted using the
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<htmlurl url="co65.html" name="co65 utility"> and statically linked. While
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this may seem overhead, it has two advantages:
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<enum>
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<item>The interface is identical to the one used for other platforms
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and to the one for the CBM 610 once it has disk I/O.
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<item>Once disk I/O is available, existing code can be changed to load drivers
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at runtime with almost no effort.
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</enum>
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<sect1>Graphics drivers<p>
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No graphics drivers are currently available for the Commodore 610 (and since
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the machine has no graphics capabilities, chances for a graphics driver aren't
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really good:-).
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<sect1>Extended memory drivers<p>
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<descrip>
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<tag><tt/cbm610-ram.emd/</tag>
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A driver for the RAM in bank 2. Supports up to 255 pages with 256 bytes
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each. Untested!
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</descrip><p>
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<sect1>Joystick drivers<p>
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The Commodore 610 is a business machine and doesn't have joystick ports. There
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are no drivers for the non existing ports available.
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<sect1>Mouse drivers<p>
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Currently no drivers available (in fact, the API for loadable mouse drivers
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does not exist).
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<sect1>RS232 device drivers<p>
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Currently no RS232 drivers exist for the Commodore 610.
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<sect>Limitations<label id="limitations"><p>
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<sect1>Disk I/O<p>
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The existing library for the CBM 610 doesn't implement C file I/O. Please note
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that this includes <tt/printf/! You may use the conio functions for screen I/O.
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To be more concrete, this limitation means that you cannot use any of the
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following functions (and a few others):
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<itemize>
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<item>fclose
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<item>fgets
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<item>fopen
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<item>fread
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<item>fprintf
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<item>fputc
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<item>fscanf
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<item>fwrite
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<item>gets
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<item>printf
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<item>...
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</itemize>
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<sect1>Kernal and hardware access<p>
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Since the program runs in bank 1, and the kernal and all I/O chips are located
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in bank 15, calling ROM routines or accessing hardware needs special code.
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<sect>Other hints<p>
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<sect1>Passing arguments to the program<p>
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Command line argument passing is currently not supported for the Commodore
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610.
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<sect>Bugs/Feedback<p>
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If you have problems using the library, if you find any bugs, or if you're
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doing something interesting with it, I would be glad to hear from you. Feel
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free to contact me by email (<htmlurl url="mailto:uz@cc65.org"
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name="uz@cc65.org">).
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<sect>License<p>
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This software is provided 'as-is', without any expressed or implied
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warranty. In no event will the authors be held liable for any damages
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arising from the use of this software.
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Permission is granted to anyone to use this software for any purpose,
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including commercial applications, and to alter it and redistribute it
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freely, subject to the following restrictions:
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<enum>
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<item> The origin of this software must not be misrepresented; you must not
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claim that you wrote the original software. If you use this software
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in a product, an acknowledgment in the product documentation would be
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appreciated but is not required.
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<item> Altered source versions must be plainly marked as such, and must not
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be misrepresented as being the original software.
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<item> This notice may not be removed or altered from any source
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distribution.
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</enum>
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</article>
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