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

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

On 07/01/2012 19:59, Laurent Sallafranque wrote:
>  > [...] to have the "micro code" of the 68030 to split each instruction
> in very small chunks (of 2 or 4 cycles) and call DSP_run every 4 cycles
> [...]
>
> Yes, that would be the best, but I'm not that sure we need to go that
> small (I think 20 should be a good approximation, as DSP needs enought
> time to generate 1 sample for the crossbar (60 cycles). A split in 60
> cycles may probably be enough.

The "problem" is that we don't get the choice :
 - either you see as a whole but you can't run dsp and cpu in "real" 
parallel mode

 - or you consider the micro code of each 68030 instruction. In that 
case, you can't choose an approximation, you must call dsp_run every 
time the number of cycles is enough to run the dsp. Running it every 20 
might work on the average, but there will always be some case where it's 
not enough.

So, it's either no split of the cpu instruction or full correct split of 
each instruction, there's no in-between solution, it would only have the 
drawbacks of the 2 others solution (slow and not neccessarily precise 
enough)

Nicolas