<!doctype linuxdoc system>

<article>
<title>PC-Engine (TurboGrafx 16) System-specific information for cc65
<author><url url="mailto:groepaz@gmx.net" name="Groepaz">,<newline>
<url url="mailto:greg.king5@verizon.net" name="Greg King">

<abstract>
An overview over the PCE runtime system as it is implemented for the
cc65 C compiler.
</abstract>

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<toc>

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<sect>Overview<p>

This file contains an overview of the PCE runtime system as it comes
with the cc65 C compiler. It describes the memory layout, PCE-specific header
files, available drivers, and any pitfalls specific to that platform.

Please note that PCE-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" might be available on
more than one platform. Please see the function reference for more
information.



<sect>Binary format<p>

The binary output file generated by the linker, for the PCE target, is an
image, with no header, that has 8K bytes in the wrong place.  That file must be
post-processed; the 8K at the end must be moved to the front of the image.

On POSIX systems, the <tt/dd/ command and the shell give a convenient way to do
it.  Here is an example of their use:
<tscreen><verb>
dd if=conio.bin bs=8K skip=3 > conio.pce
dd if=conio.bin bs=8K count=3 >> conio.pce
</verb></tscreen>
The first command grabs the last 8K of a 32K file, and writes it as the first
part of a new file.  The second command reads all but the last part of the old
file, and appends it to the new file.
<tscreen><verb>
+--------+--------+--------+--------+
| Bank 1 | Bank 2 | Bank 3 | Bank 0 |  &lt;-- "conio.bin"
+--------+--------+--------+--------+

+--------+--------+--------+--------+
| Bank 0 | Bank 1 | Bank 2 | Bank 3 |  &lt;-- "conio.pce"
+--------+--------+--------+--------+
</verb></tscreen>
<em/Note/:  That <tt/.pce/ file shows the format of the ROM cartridge that is
plugged into a PC-Engine.  But, that <tt/.bin/ file shows what programs
actually see when they execute the code in that cartridge.



<sect>Memory layout<p>

cc65-generated programs with the default setup run with the memory map that was
used by many PC-Engine games:
<itemize>
<item>The first 8K bytes is the I/O area.
<item>The second 8K bytes is RAM, which holds
<itemize>
<item>the redirected zero-page and the redirected hardware stack page,
<item>and 7680 bytes of general memory (&dollar;2200 - &dollar;3FFF).
</itemize>
<item>The last 8K bytes in the usual 64K-byte range is the ROM that holds the
program.
</itemize>

Special locations:

<descrip>
  <tag/Text screen and Font/
  The text screen is located at Video RAM (VRAM) address &dollar;0000;
  the Font is located at VRAM address &dollar;2000.

  <tag/Stack/
  The C run-time stack is located in system RAM at &dollar;3FFF;
  and, grows downwards.

  <tag/Data and BSS/
  The Data (initialized variables) and BSS (uninitialized variables) sections are
  placed one after the other into system RAM at &dollar;2200.

  <tag/Heap/
  The C heap is located after the end of the BSS section;
  and, extends up to the C run-time stack.

  <tag/Code/
  In an 8K ROM cartridge, code and read-only data are located between
  &dollar;E000 and &dollar;FFF5 in the System bank.

  In a 16K cartridge, code and read-only data are located between &dollar;C000
  and &dollar;FFF5.

  In a 32K cartridge, code and read-only data are located between &dollar;8000
  and &dollar;FFF5.
</descrip>



<sect>Platform-specific header files<p>

Programs containing PCE-specific code may use the <tt/pce.h/ header file.


<sect1>PCE-specific functions<p>

<itemize>
<item>get_tv (since all PCE systems are NTSC, this always returns TV_NTSC)</item>
<item>waitvsync</item>
</itemize>


<sect1>Hardware access<p>

The following constants, defined in the <tt/pce.inc/ include file, do
allow access to hardware that is located in the address space.

<descrip>

  <tag><tt/PSG/</tag>
  The <tt/PSG/ defines allow access to the PSG (Programmable Sound Generator).

  <tag><tt/VCE/</tag>
  The <tt/VCE/ defines allow access to the VCE chip (Video Color Encoder).

  <tag><tt/VDC/</tag>
  The <tt/VDC/ defines allow access to the VDC chip (Video Display Controller).<newline>
  32K of 16-bit words of Video RAM can be accessed only through this chip.

</descrip>



<sect>Loadable drivers<p>

All drivers must be statically linked because no file I/O is available.
The names in the parentheses denote the symbols to be used for static linking of the drivers.


<sect1>Graphics drivers<p>

No TGI graphics drivers are currently available for the PCE.


<sect1>Extended memory drivers<p>

No extended memory drivers are currently available for the PCE.


<sect1>Joystick drivers<p>

<descrip>

  <tag><tt/pce-stdjoy.joy (pce_stdjoy)/</tag>
  A joystick driver for the standard two-button joypad is available.

  Note that the Japanese 6-button pad currently is not supported.

</descrip>


<sect1>Mouse drivers<p>

No mouse drivers are currently available for the PCE.


<sect1>RS232 device drivers<p>

No serial drivers are currently available for the PCE.



<sect>Limitations<p>


<sect1>Disk I/O<p>

The existing library for the PCE doesn't implement C file
I/O. There are no hacks for the <tt/read()/ and <tt/write()/ routines.

To be more concrete, that limitation means that you cannot use any of the
following functions (and a few others):

<itemize>
<item>printf
<item>fclose
<item>fopen
<item>fread
<item>fprintf
<item>fputc
<item>fscanf
<item>fwrite
<item>...
</itemize>



<sect>Other hints<p>

Some useful resources on PCE coding:

<itemize>
<item><url url="http://blog.blockos.org/?tag=pc-engine">
<item><url url="http://pcedev.blockos.org/viewforum.php?f=5">
<item><url url="http://www.romhacking.net/?page=documents&amp;platform=4">
<item><url url="http://archaicpixels.com/Main_Page">

<item><url url="http://www.magicengine.com/mkit/doc.html">

<item><url url="https://github.com/uli/huc">
<item><url url="http://www.zeograd.com/parse.php?src=hucf">
</itemize>



<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 marked plainly 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>
