[hatari-devel] rev 3689 : splitting cpu cycles above 20

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Hello laurent

I saw your patch to split cycles when cpu cycles > 20 and call dsp on 
every chunk of 20 cycles.

Did you do this for a particular demo/game where this improves the 
emulation ? Or is this just a test ? Because I don't think doing this 
will change anything to cpu/dsp emulation.

The point is that once you know curr_cycles, it's too late to call the 
dsp in chunks of 20 cycles, because the 68030 instruction has already 
been emulated, the possible read/write were already done, so splitting 
the resulting number of cycles in chunk of 20 cycles will not help the dsp.

From the point of view of the dsp, all read/write/memory accesses made 
by the 68030 were made at cycles 0. If you split in chunk of 20 after, 
it won't change anything, the cpu has already altered its registers or 
the RAM or the data exchanged with the dsp.

What you really need is not call dsp_run more often *after* the cpu 
emulation, it's to call dsp_run every 4 or 8 cycles *while* emulating 
*every* cpu instructions (the same things that winuae does in the most 
precise 68000 cycle exact mode).

But doing that is really complicated, because you need to know the inner 
working of each 68030 instruction, and that's unfortunately not 
described in any official doc.

Nicolas