Add initial creativision.sgml, contributed by Stefan Haubenthal.

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+<!doctype linuxdoc system>
+
+<article>
+
+<title>VTech Creativision (aka Funvision) specific information for cc65
+<author><url url="mailto:polluks+cc65@sdf.lonestar.org" name="Stefan A. Haubenthal">
+<date>2016-04-14
+
+<abstract>
+An overview over the Creativision runtime system as it is implemented for the
+cc65 C compiler.
+</abstract>
+
+<!-- Table of contents -->
+<toc>
+
+<!-- Begin the document -->
+
+<sect>Overview<p>
+
+This file contains an overview of the Creativision runtime system as it comes
+with the cc65 C compiler. It describes the memory layout, Creativision specific header
+files, available drivers, and any pitfalls specific to that platform.
+
+Please note that Creativision specific functions are just mentioned here, they are
+described in detail in the separate <url url="funcref.html" name="function
+reference">. Even functions marked as "platform dependent" may be available on
+more than one platform. Please see the function reference for more information.
+
+
+<sect>Binary format<p>
+
+The standard binary output format generated by the linker for the Creativision target
+is a 4 kbyte machine language program. It is of course possible to change
+this behaviour by using one of the different linker configs.
+
+<sect>Memory layout<p>
+
+cc65 generated programs with the default setup run with the I/O area enabled,
+which gives a usable memory range of &dollar;B000 - &dollar;BEFF.
+More ROM may need additional bankswitching code.
+
+Special locations:
+
+<descrip>
+  <tag/Text screen/
+  The text screen is located at VRAM &dollar;1000.
+
+  <tag/Stack/
+  The C runtime stack is located at &dollar;3FF and growing downwards.
+
+  <tag/Heap/
+  The C heap is located at the end of the program and grows towards the C
+  runtime stack.
+
+</descrip><p>
+
+
+
+<sect>Platform specific header files<p>
+
+Programs containing Creativision specific code may use the <tt/creativision.h/ header file.
+
+
+<sect1>Creativision specific functions<p>
+
+<itemize>
+<item>bios_playsound
+<item>joystate
+<item>psg_delay
+<item>psg_outb
+<item>psg_silence
+</itemize>
+
+
+
+<!--<sect1>Hardware access<p>
+
+The following pseudo variables declared in the <tt/creativision.inc/ include file do
+allow access to hardware located in the address space.
+
+<descrip>
+
+  <tag><tt/VDP/</tag>
+  The <tt/VDP/ defines allow access to the video chip.
+
+</descrip><p>
+
+<descrip>
+
+  <tag><tt/PIA/</tag>
+  The <tt/PIA/ defines allow access to the I/O chip.
+
+</descrip><p>-->
+
+
+
+<sect>Loadable drivers<p>
+
+<sect1>Graphics drivers<p>
+
+No graphics drivers are currently available for the Creativision.
+
+
+<sect1>Extended memory drivers<p>
+
+No extended memory drivers are currently available for the Creativision.
+
+
+<sect1>Joystick drivers<p>
+
+No joystick drivers are currently available for the Creativision but <tt/joystate()/.
+
+
+<sect1>Mouse drivers<p>
+
+No mouse drivers are currently available for the Creativision.
+
+
+<sect1>RS232 device drivers<p>
+
+No communication port drivers are currently available for the Creativision.
+
+
+
+<sect>Limitations<p>
+
+<sect1>Disk I/O<p>
+
+The existing library for the Creativision doesn't implement C file
+I/O. There are even no hacks for the <tt/read()/ and <tt/write()/ routines.
+
+To be more concrete, this limitation means that you cannot use any of the
+following functions (and a few others):
+
+<itemize>
+<item>fclose
+<item>fopen
+<item>fread
+<item>fprintf
+<item>fputc
+<item>fscanf
+<item>fwrite
+<item>...
+</itemize>
+
+
+
+<sect>Other hints<p>
+
+
+
+<sect>License<p>
+
+This software is provided 'as-is', without any expressed or implied
+warranty. In no event will the authors be held liable for any damages
+arising from the use of this software.
+
+Permission is granted to anyone to use this software for any purpose,
+including commercial applications, and to alter it and redistribute it
+freely, subject to the following restrictions:
+
+<enum>
+<item> The origin of this software must not be misrepresented; you must not
+       claim that you wrote the original software. If you use this software
+       in a product, an acknowledgment in the product documentation would be
+       appreciated but is not required.
+<item> Altered source versions must be plainly marked as such, and must not
+       be misrepresented as being the original software.
+<item> This notice may not be removed or altered from any source
+       distribution.
+</enum>
+
+</article>