Re: [hatari-devel] Blitter bug in STe mode

[Eero Tamminen <oak@xxxxxxxxxxxxxx>]

Hi,

On 6/8/20 11:35 AM, Nicolas Pomarède wrote:
> Le 08/06/2020 à 10:27, Vincent Rivière a écrit :
> > On the EmuTOS mailing list we noticed a Blitter bug. It happens with 
> > Hatari, but not with Steem SSE or real STe hardware. See screenshot.
>>
> > To reproduce:
> > - put Hatari in STe mode
> > - start EmuTOS
> > - in Options menu, verify that Blitter is checked
> > - Open a drive window, and maximize it
> > - Grab it from the window title, keep mouse button pressed, and move 
> > it slowly or quickly to the right/bottom.
> >
> > Then artifacts will quickly appear.
> >
> > I can reproduce it very easily. I will give more details if you 
> > experience trouble to reproduce it.

I couldn't reproduce it with fast-forward enabled.

Fast forward needs to be disabled i.e. it's
related to (small number of) pixel movements on
*successive* VBLs.

Roger commented on emutos-devel that he couldn't
reproduce it with MegaSTE in 16MHz, only at 8Mhz,
which indicates it being (CPU <-> Blitter?) timing
related.

Window doesn't need to be fullscreen and one
doesn't need to move it partly outside of screen.

However, one needs to:
* Keep mouse button pressed for few secs before
  moving mouse
* Move mouse first to right/down, then to left
  and back. Once it starts happening, similar
  additional movements show more artifacts

Artifacts can also show for the bottom right side
of the window, not just top left side.  They can
show outside of the original window area, on both
sides, in case that matters.  See attached
screenshot.

The most interesting thing is that I couldn't get
left side artifacts to appear below first 16KB of
of screen, or right side artifacts above last 16KB
of screen.

Vincent, does EmuTOS use 16KB screen buffers for
something?


> I can't see it using emutos 0.9.9.1. Does it require a more recent 
> emutos version ?

On quick testing, I couldn't reproduce it with
that or latest EmuTOS release (v0.9.12), only
with EmuTOS Git version.

Bug is hard to trigger and somewhat timing
dependent so I can't say for sure it doesn't
happen with v0.9.12, but there have been enough
changes in EmuTOS that I'm sure you need something
newer than v0.9.9.1.

You can just take the latest 512K snapshot from:
https://sourceforge.net/projects/emutos/files/snapshots/


> In your case, can you check if the bug appears with devel version of 
> hatari and/or with latest 2.2.1 version too ?

Yes it does.

I'm not yet fully convinced it's necessarily
Hatari specific though.


	- Eero

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