Re: [hatari-devel] no more sound in falcon ?

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 31/12/2015 14:14, Douglas Little a écrit :
> Hi Nicolas.
>
>     I found the cause for the sound problem, it's related to the change
>     I made to pass a more accurate cycle count to DSP_Run. Unfortunately
>     it can't work at the moment until 68030 cycles are more accurate in
>     Hatari (by taking into account bus access time, as it's already the
>     case for 68000 STF mode).
>
>     Basically it made the DSP runs for many more cycles than what the
>     CPU ran, causing some sync problem between DSP/CPU.
>
>     I will revert the change to still get some sound in the meantime.
>
>
>
> Good news that you found the cause! I do find it a little strange though
> - because I don't use the DSP for audio. In my case, if the DSP/CPU get
> out of sync the program will lock because they are used synchronously.
> This is exactly what happens in testing if I make a mistake with the
> synchronous pattern. There are no timecritical mistakes possible without
> 'program death'. There is no non-determinism in this respect.
>
> So why CPU/DSP timing would affect codec output is unclear. Of course it
> could be affecting things earlier in the sequence - in the TOS crossbar
> init code or TOS boot sequence. Then it could begin to make more sense
> maybe... still odd though as TOS code should always synchronize
> explicitly (unlike me) and not care about actual performance of any device.

I must admit I didn't deep too much in the demo to see what part is 
sensitive to this cycles difference ; especially the difference is not 
that often, it's mostly when some hardware registers are accessed and 
some wait states must be added. If I count the wait states (and give 
more cycles to run to the DSP), sound is not here anymore, which is 
quite odd as there isn't that much IO accesses per VBL.

Well, better improving the cycles per instruction, as looking at all the 
possible issues that the differences can create could be endless :)

Nicolas