Re: [hatari-devel] DSP check freeze in Tautology II startup

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 02/07/2015 20:50, Nicolas Pomarède a écrit :
> Le 02/07/2015 20:28, Eero Tamminen a écrit :
> > Hi,
> >
> > On torstai 02 heinäkuu 2015, Nicolas Pomarède wrote:
> > > Le 02/07/2015 00:49, Eero Tamminen a écrit :
> > > > Tautology II still has DSP check freeze:
> >
> > The binary is from this package:
> >     http://rg.atari.org/files/game/t2.zip
>
> Hi
>
> my bad, I tested tautology 1, not 2 :(
>
> I confirm it freezes in CE mode but not in prefetch mode, I will see if
> I can find the difference between both, it could be some timing issue
> due to difference in cycles counting.

small update on tautology II : although games works when cache is off, I 
found that the bug is not directly related to the instruction cache 
(which is good news), but to some undocumented prefetching in 68020/30 
branch instructions that will fill 1 or 2 long words too much at the 
moment in the instruction cache (which is not good news).

This would not cause a problem in normal case, except the music player 
is using self modified code *without clearing* the instruction cache 
(this is bad ...), and in that specific case, this will trigger the rest 
of the problems in Tautology II.

I discussed this with Tony, some changes were made to fix part of this, 
but more tests are still needed to ensure this doesn't break other 
prefetching part.

Hopefully, this can be fixed when I'm back from holidays.

Nicolas