PC-Engine (TurboGrafx) System specific information for cc65

Groepaz/Hitmen,
Greg King

2018-02-12
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

5. Loadable drivers

6. Limitations

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" may 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 I/O area and a CHR bank enabled, which gives a usable memory range of $8000 - $FFF3. All boot ROM entry points may be called directly without additional code.

Special locations:

Text screen and Font

The text screen is located at VRAM $0000, the Font is located at VRAM $2000.

Stack

The C runtime stack is located in system RAM at $3FFF and growing 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, grows towards the C runtime 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

4.2 Hardware access

The following pseudo variables declared in the pce.inc include file do allow access to hardware located in the address space.

PSG

The PSG defines allow access to the PSG chip (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).

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 buttons joypad is available.

Note that the japanese 6-button pad is currently 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, this limitation means that you cannot use any of the following functions (and a few others):

7. Other hints

some useful resources on PCE coding:

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 plainly marked 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.