> What do you mean exactly with uninterrupted?
As I'm not sure what exactly causes the problem, I mean:
Don't do anything at all during the VSYNC. Just halt the
processor and let the three lines pass. Something like:
ldx #$00
lda #$02
sta VBLANK
sta WSYNC
sta VSYNC
sta WSYNC
sta WSYNC
sta WSYNC
stx VSYNC
Gas Hog is setting up a timer and keeps polling it constandly.
Indy 500 also does that, and I had problems with this game
too. I think we had quite a lot discussion about this topic
for Erik's RPG demo. And the only think he did during the VSYNC
time was to set up the timer for the VBLANK period. And his
demo caused problems for me until he moved these instuctions
out of the VSYNC time.
But I think I had problems with other games too, that don't
set up a timer. So it might have something to do with accessing
the RIOT RAM, or with keeping the TIA too busy, I don't know for
sure. Also not having VBLANK active during the VSYNC causes the
problem.
For Chris: I can try to rip the VSYNC code for one of the problematical
games out for you, if you still need it, but I guess, if you just add
a LDA #$26 / STA TIM64T between all the WSYNCs in the above example,
it might also show a difference in the signal.
> I'm doing some stuff (SWCHB, RESxy, HMMxy, NUSIZx, VDELPx) during VSYNC
> in Thrust and Jammed too and nobody reported any sync problems yet.
Well, it's a rather uncommon problem, and not too many people
own copies of your game yet. I think it might have something to
do with older TVs, where the VHOLD knob was tuned a little off.
I have a new TV now, so I can't easyly test things, but I was able
to solve the problem on my old TV for most of the games by tuning
the VHOLD knob a bit. This might be the reason, why I didn't have
a problem with your games.
My TV was a PAL model though, so I don't know, if it is the same
problem for the NTSC users. I had only problems with certain
NTSC games BTW. Their PAL counterparts synchronized nicely, even
though they used the same code for that.
Ciao, Eckhard Stolberg
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