> How do I avoid the problem you are talking about? Make sure there are an
> even number of scanlines? I think I remember you talking about not doing
> anything with the TIA during VSYNC too.
Yes, doing an even number of scanlines in every frame will avoid
the colour loss problem. You can simulate it in z26 with the -o
command line option. The newest version of Stella also simulates
it for PAL games, but you would have to create an entry in the
Stella.pro file to make your program play in PAL mode.
Unfortunately the emulators only count full scanlines, while on
real VCSs the problem might occur on different spots of unfinished
scanlines as well. So, if you have to use the emulator, you should
have the jump to the start of a new frame happen right after a
sta WSYNC at the end of the frame.
The thing with the uninterrrupted VSYNC is something I'm not
sure about. But the problems that arise from this would
normally affect badly tuned NTSC TVs rather than cause colour
loss on PAL TVs.
If you hear someone on RGVC or AtariAge complain that his game
rolls on his NTSC TV while he is sure that it is a NTSC game
and not a PAL game, and then look at the game in question, you
will notice that they are doing something during the VSYNC
period. Mostly this seems to affect games that set up a TIM8T
timer for the VSYNC period instead of doing 3 WSYNCs. But
I'm not sure if that really is the problem, or if other things
done during VSYNC might also cause problems. Therefore I'd
suggest using a VSYNC sequece like:
lda #$02
ldx #$00
sta WSYNC
sta VSYNC
sta WSYNC
sta WSYNC
sta WSYNC
stx VSYNC
if possible, since I've never heard of problems with a game
that does it this way.
Ciao, Eckhard Stolberg
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