Re: [hatari-devel] STe DMA sound

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On 15/04/2018 at 01:54, Nicolas Pomarède wrote:
I will try to look at this when I have a little more free time, but this
is clearly an example when trying to debug/improve by using the game
instead of a separate test program makes things harder to understand.
Indeed, simple unit tests are generally the best to debug things. And moreover, to avoid regressions, as already discussed elsewhere. Here (7 KHz artifact), we are facing an issue which seems to be very specific to Lethal Xcess music, where DMA operations affect YM voice C. The artifact appears and disappears as the music plays. This might be the result of an improbable combination of YM operations, DMA operations, interrupts, or whatever we can't imagine. By writing a test program without knowing the real conditions of the problem, we might be lucky and reproduce it immediately. Or not, spending a lot of time guessing what could happen.

On the other hand, with the game we have a real-world testcase. It is easy to reproduce, while a big pain to load the game each time, specially with 2 floppies. IMHO the first thing to do would be to fix the "load memory state" function to start immediately where the problem is. I tried it many times, I may have been out of luck but it never worked for me.

Finally, the whole problem just looks like a residual tune on YM voice C, while it should have been muted. With proper traces in YM emulation, I guess we could understand why that tune plays...

Vincent Rivière

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