Re: [hatari-devel] Spec512 screens with higher CPU frequencies

[Thomas Huth <th.huth@xxxxxxxxx>]

On 02/03/2019 17.15, Nicolas Pomarède wrote:
> Le 02/03/2019 à 11:29, Nicolas Pomarède a écrit :
>> Le 02/03/2019 à 08:17, Thomas Huth a écrit :
>>>
>>>   Hi all,
>>>
>>> The author of the game "Alpha Waves" reported an issue on github when
>>> running the game in 2-player mode with 32 MHz:
>>>
>>>   https://github.com/hatari/hatari/pull/2/commits/c7711fbae26295ddd288
>>>
>>> The suggested fix apparently fixes the graphical glitch in the game,
>>> but currently I wonder: Does it make sense at all that we run the
>>> spec512 with CPU frequencies > 8 MHz? The Spec512 code has definitely
>>> only been written with 8 MHz in mind, so I think we should rather not
>>> use these screen convert functions if the user selected a CPU frequency
>>> of 16 MHz of 32 MHz. Other opinions / ideas?
>>
>> Hi
>>
>> I need to look at this patch, because some times ago I fixed some
>> color timing to be able to run at other freq like 16 or 32 MHz and
>> keep the color aligned when doing plasma like effects.
>>
>> I don't think this should be limited to 8 MHz only, as someone could
>> write a demo for a 16 MHz megaste for example and on real HW you would
>> be able to align colors, which would not work anymore if we limit the
>> spec512 code to 8 MHz.
> 
> I tried this game in 2 players mode t 32 MHz, but I don't see any
> glitches with colors. Do you know which part allow to see the problem ?

Initially, both players start in the same room, and thus both parts of
the screen use the same palette. You've got to move one of the players
to a different room to see the problem: When you move one of the two
players into another room that uses a different palette, each part of
the screen should get a different palette. However, in 32 MHz, the
second part of the screen always has the same (or most of the same)
colors as the first part.

I think the problem might rather be the "CycleEnd >>= nCpuFreqShift" in
Spec512_EndScanLine() ... that looks like it is causing the update to
stop too soon. When I comment it out, the split screen in AlphaWaves
also looks fine again...

 Thomas