Help debug weird bug with sprite attribute update

By geijoenr

Master (170)

geijoenr's picture

05-07-2020, 18:08

Hi,
I am trying to debug a problem when updating sprite attributes. It looks like some vdp corruption
but I cannot figure it out.

I looks like this:

And it flickers on every raster cycle, coming back to normal sometimes.

and it happens randomly, in msx, msx2 and turboR, both in openmsx and real hardware
so indeed seems that I am doing something wrong.

The patterns are not changing, I am only writing to the attribute table.
For some of the sprites on the screen works fine, but for some others it does that...

Any clue of why this happens? I am really puzzled by this bug.

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By Sandy Brand

Master (186)

Sandy Brand's picture

05-07-2020, 19:17

Are you using double buffering? Otherwise, writing into the visible sprite attributes table while it is being scan-converted onto the screen might cause all sorts of glitches?

By geijoenr

Master (170)

geijoenr's picture

05-07-2020, 20:07

yeah, I think that is probably the problem.
I am going to try just writing to ram the attributes and copying to vram on vblank only.

By geijoenr

Master (170)

geijoenr's picture

05-07-2020, 20:40

indeed the flickering and the weird behavior is now gone, and a second issue with the way I am handling the attributes is now obvious.