PSX development

A 2-post collection

Fix for the Psy-Q Saturn SDK

If you ever want to write code for the Sega Saturn using the Psy-Q SDK (available here), you may encounter a small problem with the toolset when using #include directives.

Example:

#include "abc.h"

int main()
{
    int b = a + 43;
    return 0;
}
main.c
C:\Psyq\bin>ccsh -ITHING/ -S main.c
build.bat
int a = 98;
abc.h

This will crash with the following error: main.c:1: abc.h: No such file or directory, which is quite strange given that we explicitely told the compiler to look in that THING folder.

What we have:

  • CCSH.EXE : main compiler executable (C Compiler Super-H)
  • CPPSH.EXE preprocessor (C PreProcessor Super-H)

CCSH calls CPPSH with the source file first to get a raw code file to compile, and then actually compiles it. Here, we can see by running CPPSH alone that it still triggers the error, which means the problem effectively comes from CPPSH. After a thorough analysis in Ida, it seems that even though the code that handles parsing the command-line parameters related to include directories, those paths aren't actually added to the program's internal directory array and thus never actually used. I could have decompiled it and fixed it myself, but I found a faster and simpler way: use the PSX one.

Though CCSH and CCPSX are very different in nature (one compiles for Super-H and one for MIPS), their preprocessors are actually almost identical – when we think about it, it makes sense: the C language doesn't depend on the underlying architecture (most of the time), so why would its preprocessor do?

So here's the fix: rename CCSH to something else and copy CCPSX to CCSH. Solves all problems and finally allows compiling C code for the Sega Saturn on Windows (the only other working SDK on the Internet is for DOS, which requires using DOSBox and 8.3 filenames, which makes big projects complicated to organize).

That's nice and all but can we compile actual code? Seems that the answer is no. Here is a basic file:

#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>

int main()
{
	printf("%d\n", 42);

	return 0;
}

Compiling this will give the following error:

In file included from bin/main.c:2:
D:\SATURN\INCLUDE\stdlib.h:7: conflicting types for 'size_t'
D:\SATURN\INCLUDE\stddef.h:166: previous declaration of 'size_t'

Weird, eh?

It seems that the STDLIB.H file in the SDK is somehow wrong, in that it has the following at the top:

#ifndef	__SIZE_TYPE__DEF
#define	__SIZE_TYPE__DEF	unsigned int
typedef	__SIZE_TYPE__DEF	size_t;
#endif
STDLIB.H

Whereas its friend STDDEF.H looks like this:

#ifndef __SIZE_TYPE__
#define __SIZE_TYPE__ long unsigned int
#endif
#if !(defined (__GNUG__) && defined (size_t))
typedef __SIZE_TYPE__ size_t;
#endif /* !(defined (__GNUG__) && defined (size_t)) */
STDDEF.H

Two incompatible declarations, the compiler dies. The simple fix is to remove the DEF at the end of the names in STDLIB.H, to get something like this:

#ifndef	__SIZE_TYPE__
#define	__SIZE_TYPE__	unsigned int
typedef	__SIZE_TYPE__	size_t;
#endif
STDLIB.H

Paella, or how to emulate PSX games in Windows CE userland

Lately, I've been decompiling Tomb Raider 5 with some friends and while researching potential sources of debug informations that could help the process, I stumbled upon the Pocket PC version of Tomb Raider 1. It was ported by Ideaworks3D, a London-based game development company specialized in porting.

It's supposed to run on low-performance handheld devices running Windows Mobile/CE 5.0 and thus one would imagine that they have simply taken the Windows code and tweaked it a little bit to make it run on CE. Well as I discovered, it's more complicated than that. First, there is no Windows version of TR1, it was only released for DOS and was never ported to either Win16 or Win32. Second, they actually didn't take the PC version as a base, but the PSX version.

It may seem weird, why take the PSX version if your product is going to run on Windows CE. As it appears, Ideaworks3D seems to have developed an in-house userland syscall JIT translator for PSX, and uses it when porting games to CE. In other words, they compile the PSX codebase to ARM code and link that binary against a DLL file called iepaella.dll which contains implementations of PSX syscalls that call the WinCE API. Apparently, they have also made a version of that DLL which runs on standard Win32 that they used to make an ActiveX port of their Pocket PC port of the PSX version. It allowed playing TR1 in Internet Explorer. Not sure why anyone would ever do that, though.

I find this quite interesting because the main game executable seems to have a code near-identical to the original PSX version, which means that "IEPaella" is effectively a full-featured userland PSX emulator for WinCE and Win32 that is capable of mapping the PSX system routines to DirectX API calls. I haven't been able to find any other similar product on the internet. The only software that could be considered similar is Usercorn, a userland emulator based on Unicorn which implements most of the Linux, BSD and Darwin syscalls and even some DOS interrupts. It's very basic though, nowhere near what Paella does.

Currently, the codebase of the decompilation project is divided in 3 main folders:

  • GAME contains the shared game code
  • SPEC_PSX contains the PSX platform code
  • SPEC_PC contains the PC platform code

Debugging on PSX is much harder than on PC, because the binary is run in an emulator and you can't just run the code step-by-step to see where it crashes. Using Paella would allow doing such a thing because the binary is effectively being run on the computer and works like any other C++ program. We're currently search for ways to implement Paella support in TOMB5, but it may take time because not all PSX syscalls are implemented. It will eventually work, though.