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SCU DSP documentation

jollyroger - May 15, 2017

		jollyroger	May 15, 2017
		Hello everyone, Given that it is common knowledge that the Sega official documentation for the SCU DSP contains several mistakes, could we gather here all we know about this so that we create and maintain an "errata"? I would find it useful, and I hope others would too... Cheers, Jolly

		vbt	May 15, 2017
		sure and you're welcome here !

		jollyroger	May 17, 2017
		Thank you vbt I am looking at the gurus here, please share your information, it would be really precious! I haven't had too much time with the DSP back in the day and I lost all my notes... Jolly

		jollyroger	May 18, 2017
		Come on guys, no love for this? Cyber? Antime?

		mrkotfw	May 19, 2017
		You're more than welcome to look in the MESS/MAME/Mednafen/Yabause source code and document them here. The fact that CWX, Guillaume, antime, and numerous others have done a lot of work to actually implement the processor, it would be great if you would get the ball rolling here. I would start with enumerating the instruction set and making corrections on the PDF itself.

		jollyroger	May 19, 2017
		mrkotfw said: Sounds good, it will just take me much longer to do that if they did it, as I have to compare each operation documented in the PDF with the implementation in the emulator to find discrepancies, whereas the authors certainly know which ones they had to make corrections to. If noone else takes this up, I will do it, over time... Jolly

		ExCyber	May 21, 2017
		You pinged me via PM, but since there's a thread I guess I'll just post my response here. I tried to dig up some documentation/tools back in the day, and always wanted to try a "DMA 'through' the SCU DSP" method (i.e. SCU DMA directly to the DSP data port, which I thought should work), but I never really did much directly with it. I'd suggest cross-referencing the history of the Yabause SCU code with the manual and see if you find any errors that way: https://github.com/Yabause/yabause/commits/master/... Another way to slice this information is to look at the blame data, which lets you correlate commits to lines of code; the main DSP code seems to start here, and has some comments suggestive of errors in old versions of some opcodes: https://github.com/Yabause/yabause/blame/master/ya...

		jollyroger	May 21, 2017
		Hey, I pinged you on PM just because I could not be sure you would be tracking this thread, thanks for your reply. That makes a lot of sense, I will try to read through the code changes and at the same time I will try to remember from when I was actually programming the Saturn back then, as I had noticed discrepancies in the documentation, but I forgot all about it...

		cafe-alpha	May 26, 2017
		I don't know if it what you're looking for, but a long ago @antime... did some documentation and reverse engineering work regarding SCU DSP. I couldn't find it directly on antime's homepage, but this is located in SaturnOrbit archive -> TOOLS -> scu-dump.txt and scu-dump_src.rar

		itsstillthinking	May 29, 2017
		jollyroger said: Off topic but welcome jolly

		jollyroger	May 29, 2017
		itsstillthinking said: Thanks