Re: [hatari-devel] Issues with cache hits/misses?

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 30/05/2015 21:35, Eero Tamminen a écrit :
> Things don't work correctly with GEMDOS HD emulation:
> - Name of the first file in a directory is shown for all files
> - About every program I tried to run in TOS v4 gives error #35,
>    probably for same reason
>
> I can run programs from disk images though.
>
> What GEMDOS HD emulation should do in presence of data cache, when
> it modifies emulated memory (e.g. DTA) according to the requested
> OS call?

Hi

it seems my tests were too quick :) This is fixed, data cache should be 
flushed when HD emulation (or any other part) directly writes to memory.


> > But note that this will be *very, very slow*. Managing the cache takes a
> > lot of cpu
>
> I profiled Hatari and compared how much DSP emulation cost changes
> in relation to m68k emulation cost.  Based on that I calculated that
> the 030 cache handling added 10-20% overhead (closer to 10%).
>
> More interestingly, EmuTOS and TOS v3 seems to work at OK speed.
>
> It's only TOS v4 that is really slow.  Either TOS v4 breaks with
> data cache, or Hatari emulation (VBL timing?) doesn't work with
> TOS v4.

I don't know yet, but we can clearly see that even during the early 
memory tests at boot in falcon mode, the screen refresh is very slow (we 
see red and yellow Atari logo, because all 4 planes are not copied fast 
enough to get the 'black' color in one go).
So, this looks more like a 10 times slowdown than just a 10-20% overhead.

> While emulation doesn't work with it as well as without, it's
> better to disable data cache by default and have it enabled only
> with some option saying "experimental" or "experts only"
> (nothing in GUI).

I will have a look at this, I want to make more tests before with the 
data cache.


Nicolas