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<!doctype linuxdoc system>
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<article>
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<title>Nintendo Entertainment System 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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Stefan A. Haubenthal, <htmlurl url="mailto:polluks@sdf.lonestar.org" name="polluks@sdf.lonestar.org">
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<date>2005-07-17
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<abstract>
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An overview over the NES 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 NES runtime system as it comes
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with the cc65 C compiler. It describes the memory layout, NES specific header
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files, available drivers, and any pitfalls specific to that platform.
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Please note that NES 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 NES target
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is a machine language program with an INES cartridge header. 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 with the default setup run with the I/O area and a
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CHR bank enabled, which gives a usable memory range of $8000 - $FFF3.
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All boot 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 VRAM $2000.
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<tag/Stack/
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The C runtime stack is located at $7FFF 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 NES specific code may use the <tt/nes.h/ header file.
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<sect1>NES specific functions<p>
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<itemize>
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<item>waitvblank
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<item>get_tv
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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/nes.inc/ include file do
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allow access to hardware located in the address space.
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<descrip>
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<tag><tt/PPU/</tag>
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The <tt/PPU/ defines allow access to the PPU chip.
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<tag><tt/APU/</tag>
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The <tt/APU/ defines allow access to the APU chip.
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</descrip><p>
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<sect>Loadable drivers<p>
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All drivers must be statically linked because no file I/O is available.
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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/nes-64-56-2.tgi (nes_64_56_2)/</tag>
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This driver features a resolution of 64×56 with 2 colors using the
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CHR bank.
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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 NES.
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<sect1>Joystick drivers<p>
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<descrip>
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<tag><tt/nes-stdjoy.joy (nes_stdjoy)/</tag>
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A joystick driver for the standard four buttons joypad is available.
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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 NES.
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<sect1>RS232 device drivers<p>
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No serial drivers are currently available for the NES.
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<sect>Limitations<p>
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<sect1>Disk I/O<p>
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The existing library for the NES doesn't implement C file
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I/O. There are no hacks for the <tt/read()/ and <tt/write()/ routines.
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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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<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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