Re: [hatari-devel] WinUAE CPU core cycle-exact option impact for 68000

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 15/01/2020 à 22:49, Eero Tamminen a écrit :
> Hi,
>
> I'd like to clarify in the Hatari manual what
> the impact of cycle-exact option is for 68000.
>
> I see that Hatari's cycle-exact option enables
> both CPU and memory cycle-exact options from
> the WinUAE CPU core.
>
> WinUAE CPU core uses different functions for
> instruction and exception handling when cycle-
> exact is enabled, but what's the actual impact
> of those for the speed of the emulated code?

Hi

that's sthg I'm planning to measure one day. The impact on exception 
should not be noticable (they don't happen that often compared to 
"normal" instructions).
Note that I have a devel tree not committed yet with even more CE 
behaviour, including very accurate bus error emulation (that Toni/WinUAE 
improved extensively in the latest weeks/months).

This might have an impact too, maybe not that much in the end, but I'm 
planning to measure it too.


>      - Eero
>
> (For 68030+, impact of cache dwarfs anything else,
> and programs are less cycle-accuracy dependent,
> so there those details aren't needed so much I
> think.)

Cache and mmu + CE are really adding a lot of overhead in the code for 
>= 68020 and this can be seen with a slower emulation. Enabling CE with 
just 68000 is not that CPU hungry.

Nicolas