mirror of https://github.com/cc65/cc65.git
304 lines
8.8 KiB
Plaintext
304 lines
8.8 KiB
Plaintext
<!doctype linuxdoc system>
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<article>
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<title>Commodore VIC20 (aka VC20 aka VIC1001) 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">
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<abstract>
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An overview over the VIC20 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 VIC20 runtime system as it comes with the
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cc65 C compiler. It describes the memory layout, VIC20-specific header files,
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available drivers, and any pitfalls specific to that platform.
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Please note that VIC20-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 VIC20 target
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is a machine language program with a one line BASIC stub, which calls the
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machine language part via SYS. This means that a program can be loaded as
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BASIC program and started with RUN. It is of course possible to change this
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behaviour by using a modified startup file and linker config.
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<sect>Memory layout<p>
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cc65 generated programs with the default setup run with unexpanded memory
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(RAM at $A000 - $BFFF may be used for the heap),
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which gives a usable memory range of $1000 - $1DFF.
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All ROM entry points may be called directly without additional code.
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Special locations:
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<descrip>
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<tag/Text screen/
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The text screen is located at $1E00 (as in the standard setup).
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<tag/Stack/
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The C runtime stack is located at $1DFF 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 VIC20-specific code may use the <tt/vic20.h/ or <tt/cbm.h/
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header files. Using the later may be an option when writing code for more than
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one CBM platform, since it includes <tt/vic20.h/ and declares several functions
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common to all CBM platforms.
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<sect1>VIC20-specific functions<p>
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There are currently no special VIC20 functions.
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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 <url url="funcref.html" name="function reference"> for
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declaration and usage.
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<itemize>
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<item>cbm_close
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<item>cbm_closedir
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<item>cbm_k_setlfs
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<item>cbm_k_setnam
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<item>cbm_k_load
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<item>cbm_k_save
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<item>cbm_k_open
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<item>cbm_k_close
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<item>cbm_k_readst
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<item>cbm_k_chkin
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<item>cbm_k_ckout
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<item>cbm_k_basin
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<item>cbm_k_bsout
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<item>cbm_k_clrch
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<item>cbm_k_tksa
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<item>cbm_k_second
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<item>cbm_load
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<item>cbm_open
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<item>cbm_opendir
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<item>cbm_read
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<item>cbm_readdir
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<item>cbm_save
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<item>cbm_write
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<item>get_tv
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<item>waitvsync
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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/vic20.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/VIC/</tag>
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The <tt/VIC/ structure allows access to the VIC (the graphics
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controller). See the <tt/_vic.h/ header file located in the include
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directory for the declaration of the structure.
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<tag><tt/VIA1, VIA2/</tag>
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Access to the two VIA (versatile interface adapter) chips is available via
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the <tt/VIA1/ and <tt/VIA2/ variables. The structure behind these variables
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is explained in <tt/_6522.h/.
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<tag><tt/COLOR_RAM/</tag>
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A character array that mirrors the color RAM of the VIC20 at $9600.
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</descrip><p>
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<sect>Loadable drivers<p>
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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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<descrip>
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<tag><tt/vic20-hi.tgi (vic20_hi_tgi)/</tag>
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This driver features a resolution of 160×192 with two colors. The
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background can be chosen from a sixteen-color palette. The foreground can
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be chosen from an eight-color palette.
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The driver will use memory from addresses $1000 to $1FFF as a graphics
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buffer. Therefore, the VIC-20 must have, at least, 8K of expansion RAM.
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Programs that use this driver must be linked by the <tt/vic20-tgi.cfg/
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configuration file. It will link a special header into the program.
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That header will do the housekeeping that's needed by TGI.
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An example command line:
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<tscreen><verb>
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cl65 -D DYN_DRV=0 -t vic20 -C vic20-tgi.cfg samples/mandelbrot.c
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</verb></tscreen>
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When the program starts, it will move itself up in RAM, to make room for the
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buffer. When the program finishes, it will reset the BASIC interpreter.
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That means that graphics pictures won't be preserved between the executions
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of programs. Also, the graphics buffer shares RAM with the text screen. If
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a picture must be saved, then a program must put it somewhere else (such as
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a disk file) before returning to the text mode.
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</descrip>
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<sect1>Extended memory drivers<p>
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<descrip>
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<tag><tt/vic20-rama.emd (vic20_rama_emd)/</tag>
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A driver for any RAM at $A000-$BFFF. Supports 32 256 byte pages.
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Written and contributed by Marco van den Heuvel.
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<tag><tt/vic20-georam.emd (vic20_georam_emd)/</tag>
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A driver for the Berkeley Softworks GeoRam cartridge connected by means of
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the MasC=erade c64 cartridge adapter. The driver will determine the
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available RAM from the connected cartridge. It supports 64KB
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up to 2048KB of RAM.
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</descrip><p>
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<sect1>Joystick drivers<p>
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The default drivers, <tt/joy_stddrv (joy_static_stddrv)/, point to <tt/vic20-stdjoy.joy (vic20_stdjoy_joy)/.
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<descrip>
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<tag><tt/vic20-stdjoy.joy (vic20_stdjoy_joy)/</tag>
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Supports one standard joystick connected to the joysticks port of the VIC20.
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<tag><tt/vic20-ptvjoy.joy (vic20_ptvjoy_joy)/</tag>
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Driver for the Protovision 4-player adapter contributed by Groepaz. See
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<url url="https://www.protovision.games/hardw/4_player.php"
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name="the Protovision shop"> for prices and building instructions. Up to three
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joysticks are supported.
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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 VIC20.
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<sect1>RS232 device drivers<p>
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No VIC1011 drivers are currently available for the VIC20.
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<sect>Limitations<p>
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<sect1>Escape code<p>
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The CTRL key cannot be used to type most control characters,
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entering an Esc is not possible.
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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 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>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>Program return code<p>
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The program return code (low byte) is passed back to BASIC by use of the
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<tt/ST/ variable.
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<sect1>Using extended memory<p>
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BLK5 memory may be added to the heap by using the following code:
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<tscreen><verb>
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/* Check for the existence of RAM */
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if (PEEK(0xA000) == POKE(0xA000, PEEK(0xA000)+1)) {
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/* Add it to the heap */
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_heapadd ((void *) 0xA000, 0x2000);
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}
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</verb></tscreen>
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<sect1>Interrupts<p>
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The runtime for the VIC20 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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