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293 lines
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Plaintext
293 lines
9.0 KiB
Plaintext
<!doctype linuxdoc system>
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<article>
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<title>Oric Atmos-specific information for cc65
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<author>
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<url url="mailto:uz@cc65.org" name="Ullrich von Bassewitz">,<newline>
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<url url="mailto:polluks@sdf.lonestar.org" name="Stefan A. Haubenthal">,<newline>
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<url url="mailto:greg.king5@verizon.net" name="Greg King">
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<abstract>
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An overview over the Atmos runtime system as it is implemented for the cc65 C
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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 Atmos runtime system as it comes with the
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cc65 C compiler. It describes the memory layout, Atmos-specific header files,
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available drivers, and any pitfalls specific to that platform.
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Please note that Atmos-specific functions are just mentioned here, they are
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described in detail in the separate <url 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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<sect>Binary format<p>
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The standard binary output format generated by the linker for the Atmos target
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is a machine language program with a one-line BASIC stub that jumps to the
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machine-language part through <tt/CALL/. It has one sacrificial byte attached
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to the end (a bug in the Oric ROM means that BASIC can put a variable on top
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of the last byte that was loaded). It has a 24-byte tape header. A file can
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be CLOADed as a BASIC program, and started by typing <tt/RUN/. The standard
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load address is $501.
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<sect>Memory layout<p>
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In the standard setup, cc65-generated programs use the memory from
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$0501 to $9800; so, nearly 37K of memory (including the stack) is
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available. ROM calls are possible without further precautions.
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If your program needs more memory, and it won't use TGI graphics, then you can
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use the ld65 command-line option, <tt/-D __GRAB__=1/, when building the
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program, to include the graphics screen RAM. Then, nearly 44K of memory
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($0501 to $B400) is available.
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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 $97FF (or $B3FF), and grows
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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 Atmos-specific code may use the <tt/atmos.h/ header file.
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<sect1>Atmos-specific functions<p>
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The functions listed below are special for the Atmos. See the <url
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url="funcref.html" name="function reference"> for declaration and usage.
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<itemize>
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<item>atmos_load
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<item>atmos_save
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<item>atmos_explode
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<item>atmos_ping
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<item>atmos_shoot
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<item>atmos_tick
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<item>atmos_tock
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<item>atmos_zap
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</itemize>
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<sect1>Hardware access<p>
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The following pseudo variables declared in the <tt/atmos.h/ header file do allow
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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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<descrip>
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<tag><tt/VIA/</tag>
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Access to the VIA (Versatile Interface Adapter) chip is available via the
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<tt/VIA/ variable. The structure behind this variable is explained in <tt/_6522.h/.
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</descrip><p>
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<sect>Loadable drivers<p>
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<em>Note:</em> Since the Atmos doesn't have working disk I/O
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(see <ref id="limitations" name="section "Limitations"">), the
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available drivers cannot be loaded at runtime (so the term "loadable drivers"
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is somewhat misleading). Instead, the drivers have to be 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 Atmos 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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The names in the parentheses denote the symbols to be used for static linking of the drivers.
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<sect1>Graphics drivers<p>
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The default drivers, <tt/tgi_stddrv (tgi_static_stddrv)/,
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point to <tt/atmos-240-200-2.tgi (atmos_240_200_2_tgi)/.
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<descrip>
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<tag><tt/atmos-228-200-3.tgi (atmos_228_200_3_tgi)/</tag>
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This driver was written by Greg King and Stefan Haubenthal.
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It features a resolution of 228×200 with a palette of two colors that
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can be chosen from the Atmos's eight colors. The driver supports a third
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palette-"color" that actually "flips" the pixel (it becomes the other color)
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that is on the screen under the graphics cursor.
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<tag><tt/atmos-240-200-2.tgi (atmos_240_200_2_tgi)/</tag>
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This driver was written by Stefan Haubenthal and Greg King.
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It features a resolution of 240×200 with black and white colors.
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It is the default graphics driver for the Atmos.
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</descrip><p>
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<sect1>Extended memory drivers<p>
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No extended memory drivers are currently available for the Atmos.
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<sect1>Joystick drivers<p>
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<descrip>
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<tag><tt/atmos-pase.joy (atmos_pase_joy)/</tag>
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Supports two standard joysticks connected to a P.A.S.E. / Altai interface of the Atmos.
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<tag><tt/atmos-ijk.joy (atmos_ijk_joy)/</tag>
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Supports two standard joysticks connected to an IJK interface of the Atmos.
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</descrip><p>
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<sect1>Mouse drivers<p>
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No mouse drivers are currently available for the Atmos.
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<sect1>RS232 device drivers<p>
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<descrip>
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<tag><tt/atmos-acia.ser (atmos_acia_ser)/</tag>
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Driver for the Telestrat integrated serial controller and the Atmos with a
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serial add-on.
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Note that, because of the peculiarities of the 6551 chip, together with the
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use of the NMI, transmits are not interrupt driven; and, the transceiver
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blocks if the receiver asserts flow control because of a full buffer.
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</descrip><p>
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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 Atmos doesn't implement C file I/O. There are
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hacks for the <tt/read()/ and <tt/write()/ routines in place, which will make
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functions work that read from <tt/stdin/ and write to <tt/stdout/ and
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<tt/stderr/ (such as <tt/printf()/). However, those functions have some
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shortcomings which won't be fixed, because they're going to be replaced
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anyway.
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To be more concrete, that 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>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>...
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</itemize>
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<sect>Other hints<p>
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<sect1>Function keys<p>
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They are defined to be FUNCT + a number key.
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<sect1>Capitals lock<p>
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The keyboard's "CAPS Lock" mode is turned off while the program is running.
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The previous mode (usually, CAPS Lock turned on [because Oric BASIC keywords
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must be UPPER-case]) is restored when the program stops.
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<sect1>Passing arguments to the program<p>
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Command-line arguments can be passed to <tt/main()/. Since that is not
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supported directly by BASIC, the following syntax was chosen:
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<tscreen><verb>
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RUN:REM arg1 " ARG2 IS QUOTED" ARG3 "" ARG5
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</verb></tscreen>
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<enum>
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<item>You must turn <tt/CAPS/ lock off (tap CTRL-T) when you want to type
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lower-case arguments (but, <tt/RUN/ and <tt/REM/ must be UPPER-case).
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<item>Arguments are separated by spaces.
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<item>Arguments may be quoted.
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<item>Leading and trailing spaces around an argument are ignored. Spaces within
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a quoted argument are allowed.
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<item>The first argument passed to <tt/main()/ is the program name.
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<item>A maximum number of 10 arguments (including the program name) are
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supported.
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</enum>
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<sect1>Automatic starting<p>
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Usually, a cc65-built program just will sit quietly in memory, after it is
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CLOADed. It waits for you to start it (by typing BASIC's <tt/RUN/ command).
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But, if you want to create a program that will start running immediately after
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it is loaded, then you can use the linker command-line option
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<tt/-D __AUTORUN__=$C7/.
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<sect1>Interrupts<p>
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The runtime for the Atmos uses routines marked as <tt/.INTERRUPTOR/ for
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interrupt handlers. Such routines must be written as simple machine language
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subroutines and will be called automatically by the interrupt handler code
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when they are linked into a program. See the discussion of the <tt/.CONDES/
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feature in the <url url="ca65.html" name="assembler manual">.
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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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