Re: [hatari-devel] STe DMA sound

[Vincent Rivière <vincent.riviere@xxxxxxxxxxx>]

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