From: "Dennis Debro" > No need to comment this out as I've found the
problem. It's VBLANK again.
> For the title screen you're starting VBLANK at cycle 13. I moved this to
> right after the WSYNC so it starts at cycle 0 and the screen syncs
perfectly
> now.
>
> I guess there is still information to be gathered on this register.
Based on the TV signal, VSYNC has to be asserted before the horizontal sync
pulse ends. This causes the horizontal sync pulse to be turned into a
serration pulse. Worst case, the STA VSYNC has to end on cycle 10 after the
STA WSYNC. (Based on the NTSC spec, some calculations and assumptions.)
Note: there may be TIA limitations which would require the VSYNC to be
asserted (and released) earlier, i.e. immediately after STA WSYNC.
I'd have to do some digging, but there were some strange problems reported
with Skeleton/Skeleton+ where VSYNC may have been an issue. I wonder if
this is something which could very slightly between TIA versions.
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