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<!doctype linuxdoc system>
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<article>
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<title>Oric Atmos specific information for cc65
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<author>Ullrich von Bassewitz <htmlurl url="mailto:uz@cc65.org" name="uz@cc65.org"><newline>
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Stefan A. Haubenthal <htmlurl url="mailto:polluks@sdf.lonestar.org" name="polluks@sdf.lonestar.org"><newline>
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<url url="mailto:greg.king5@verizon.net" name="Greg King">
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<date>2013-01-08
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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 <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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<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 17 byte tape header including a cc65 tag.
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The standard load and autostart address is $500.
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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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$500 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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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 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 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 <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>atmos_load
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<item>atmos_save
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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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<descrip>
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<tag><tt/atmos-228-200-3.tgi (atmos_228_200_3)/</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)/</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)/</tag>
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Supports two standard joysticks connected to the P.A.S.E. 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)/</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
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I/O. There is one hack for the <tt/write()/ routine in
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place, which will make functions work that write to <tt/stdout/
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(like <tt/printf()/). However, this function has some shortcomings which
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won't be fixed, because it's going to be replaced anyway.
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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>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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These are defined to be FUNCT + number key.
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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 this is not
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supported by BASIC, the following syntax was chosen:
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<tscreen><verb>
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CALL#500: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>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 <htmlurl url="ca65.html" name="assembler manual">.
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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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