[ARCADE] SuperModel WIP

July 13, 2011

Frequently, the best way to solve a frustrating problem is to step away from it for a long while. Then, you'll be able to look at it with a fresh pair of eyes. For a couple weeks, I was getting very frustrated with my inability to get the Model 3's sound board to produce audio, even when feeding it MIDI commands directly. Then, the other day, while searching for the code that instructs the sound processor to play a loaded sample, I stumbled across a bug in my old 68K emulator that I had never caught before. It turns out that logical shifts behave differently on the 68K and X86 architectures when the shift count exceeds the register width. On the 68K, the result will be 0, but on X86, it is undefined and can leave the register unmodified! This was causing an important code path in Scud Race's sound driver to fail.

Fast forward a few days, Nik and I have not only got the Model 3 sound board generating audio for many games, we've figured out how the PowerPC and 68K communicate. We've even got a build with sound output up and running, although it's still a bit jittery now and then due to the overhead introduced by the sound board emulation. We're also now using Karl Stenerud's excellent Musashi 68K emulator, which although slower than Turbo68K, works in both 64- and 32-bit builds. There are still some bugs and performance issues to work out, and the MPEG board is not yet emulated, but stay tuned! Slowly but surely, we're on it.