# PC-Engine (TurboGrafx 16) System-specific information for cc65

## Groepaz/Hitmen,
Greg King

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

## 1. Overview

## 2. Binary format

## 3. Memory layout

## 4. Platform-specific header files

- 4.1 PCE-specific functions
- 4.2 Hardware access

## 5. Loadable drivers

- 5.1 Graphics drivers
- 5.2 Extended memory drivers
- 5.3 Joystick drivers
- 5.4 Mouse drivers
- 5.5 RS232 device drivers

## 6. Limitations

- 6.1 Disk I/O

## 7. Other hints

## 8. License

## 1. Overview

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 function reference. Even functions marked as "platform dependent" might be available on more than one platform. Please see the function reference for more information.

## 2. Binary format

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 `dd` command and the shell give a convenient way to do it. Here is an example of their use:

> `

>     dd if=conio.bin bs=8K skip=3 > conio.pce
>     dd if=conio.bin bs=8K count=3 >> conio.pce

> `

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.

> `

>     +--------+--------+--------+--------+
>     | Bank 1 | Bank 2 | Bank 3 | Bank 0 |  <-- "conio.bin"
>     +--------+--------+--------+--------+

>     +--------+--------+--------+--------+
>     | Bank 0 | Bank 1 | Bank 2 | Bank 3 |  <-- "conio.pce"
>     +--------+--------+--------+--------+

> `

Note: That `.pce` file shows the format of the ROM cartridge that is plugged into a PC-Engine. But, that `.bin` file shows what programs actually see when they execute the code in that cartridge.

## 3. Memory layout

cc65-generated programs with the default setup run with the memory map that was used by many PC-Engine games:

- The first 8K bytes is the I/O area.
- The second 8K bytes is RAM, which holds
  - the redirected zero-page and the redirected hardware stack page,
  - and 7680 bytes of general memory ($2200 - $3FFF).
- The last 8K bytes in the usual 64K-byte range is the ROM that holds the program.

Special locations:

Text screen and Font

  The text screen is located at Video RAM (VRAM) address $0000; the Font is located at VRAM address $2000.

Stack

  The C run-time stack is located in system RAM at $3FFF; and, grows downwards.

Data and BSS

  The Data (initialized variables) and BSS (uninitialized variables) sections are placed one after the other into system RAM at $2200.

Heap

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

Code

  In an 8K ROM cartridge, code and read-only data are located between $E000 and $FFF5 in the System bank.

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

  In a 32K cartridge, code and read-only data are located between $8000 and $FFF5.

## 4. Platform-specific header files

Programs containing PCE-specific code may use the `pce.h` header file.

## 4.1 PCE-specific functions

- get_tv (since all PCE systems are NTSC, this always returns TV_NTSC)
- waitvsync

## 4.2 Hardware access

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

`PSG`

  The `PSG` defines allow access to the PSG (Programmable Sound Generator).

`VCE`

  The `VCE` defines allow access to the VCE chip (Video Color Encoder).

`VDC`

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

## 5. Loadable drivers

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.

## 5.1 Graphics drivers

No TGI graphics drivers are currently available for the PCE.

## 5.2 Extended memory drivers

No extended memory drivers are currently available for the PCE.

## 5.3 Joystick drivers

`pce-stdjoy.joy (pce_stdjoy)`

  A joystick driver for the standard two-button joypad is available.

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

## 5.4 Mouse drivers

No mouse drivers are currently available for the PCE.

## 5.5 RS232 device drivers

No serial drivers are currently available for the PCE.

## 6. Limitations

## 6.1 Disk I/O

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

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

- printf
- fclose
- fopen
- fread
- fprintf
- fputc
- fscanf
- fwrite
- ...

## 7. Other hints

- Mednafen is a good emulator to use for the PC-Engine.

Some useful resources on PCE coding:

- http://blog.blockos.org/?tag=pc-engine
- http://pcedev.blockos.org/viewforum.php?f=5
- http://www.romhacking.net/?page=documents&platform=4
- http://archaicpixels.com/Main_Page
- http://www.magicengine.com/mkit/doc.html
- https://github.com/uli/huc
- http://www.zeograd.com/parse.php?src=hucf

## 8. License

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:

1. 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.
2. Altered source versions must be marked plainly as such; and, must not be misrepresented as being the original software.
3. This notice may not be removed or altered from any source distribution.