Sunday, September 18, 2016

Super Turrican - MSU Hack

Last year i got myself a sd2snes flash card and soon figured out that there is a feature called MSU. It's a soundchip which is capable of playing raw wave files from an sd card just by writing in a register which song number to play.

Now we have a wide variety of MSU patches available which make games like Mega Man X and Super Mario World use it to play their background music.
It's kinda something the Mega Drive got with the MegaCD but with sd cards instead.

Last year after meeting Chris Hülsbeck, i thought.... Super Turrican really is in need for a MSU hack but there wasn't any.
I've read about higane which is an emulator capable of simulating the MSU (or invented it in the first place???) and got the source code of it.
Using the integrated tracer and a few mods i've disassembled the functions of Super Turrican in charge for SPC control and replaced them with my own. Luckily there was enough space left on the ROM to place them.

Now whenever the game says "play song X" i analyze this call using a table and in case there is a wave file for that song on the sd card it is played. Otherwise the original process continues and the song is played using the SPC.

Some gameplay footage can be found on YouTube.

I really like to publish the whole package here.... stay tuned.

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