Hi Glenn!
>Manuel, it looks like Gunfight is taking up too much
calculation time
>during VBLANK or OVERSCAN because the screen is jerking
up one or two
>scanlines during the opening music or when processing
controller moves or
>gunshots during gameplay.
Using too many cycles definitely can't be the source
causing any jerking in Gunfight. Even in a worst case
scenario there's 10+ pure idle scannlines during VBLANK
and another 20+ idle scannlines during the Overscan,
where I'm just waiting for the timer to finish. I think
I'm very close to generating 262 frames too.
>This may not be visible in PAL or emulators, but it is
on NTSC on the real
>thing.
Out of the Z26 log I find this odd looking sequences
around VSYNC:
Here it seems I'm doing 262 scannlines:
( 5 261 57 103) ( 10 123 8 8 22) nvbdIzc 01 ff 04
fd f4a7: ad 84 02 lda INTIM
( 5 261 61 115) ( 10 123 8 8 22) nvbdIZc 00 ff 04
fd f4aa: d0 fb bne f4a7
( 5 261 63 121) ( 10 123 8 8 22) nvbdIZc 00 ff 04
fd f4ac: 60 rts
( 5 261 69 139) ( 10 123 8 8 22) nvbdIZc 00 ff 04
ff f251: 4c 7d f2 jmp f27d
( 5 261 72 148) ( 10 123 8 8 22) nvbdIZc 00 ff 04
ff f27d: 84 02 sty WSYNC
( 5 262 0 -68) ( 10 123 8 8 22) nvbdIZc 00 ff 04
ff f27f: a0 02 ldy #02
( 5 262 2 -62) ( 10 123 8 8 22) nvbdIzc 00 ff 02
ff f281: 84 00 sty VSYNC
( 6 1 5 -53) ( 10 123 8 8 22) nvbdIzc 00 ff 02
ff f283: 84 02 sty WSYNC
Here it seems I'm doing 263 scannlines:
( 1 261 60 112) ( 11 123 0 0 22) nvbdIzc 01 ff 14
fd f4a7: ad 84 02 lda INTIM
( 1 261 64 124) ( 11 123 0 0 22) nvbdIZc 00 ff 14
fd f4aa: d0 fb bne f4a7
( 1 261 66 130) ( 11 123 0 0 22) nvbdIZc 00 ff 14
fd f4ac: 60 rts
( 1 261 72 148) ( 11 123 0 0 22) nvbdIZc 00 ff 14
ff f251: 4c 7d f2 jmp f27d
( 1 261 75 157) ( 11 123 0 0 22) nvbdIZc 00 ff 14
ff f27d: 84 02 sty WSYNC
( 1 262 76 160) ( 11 123 0 0 22) nvbdIZc 00 ff 14
ff f27f: a0 02 ldy #02
( 1 263 2 -62) ( 11 123 0 0 22) nvbdIzc 00 ff 02
ff f281: 84 00 sty VSYNC
( 2 1 5 -53) ( 11 123 0 0 22) nvbdIzc 00 ff 02
ff f283: 84 02 sty WSYNC
It seems that it's possible that I'm already stepping
onto a new scannline, between moment the counter expires
and hitting VSYNC.
Since, as Eckhard suggested lately, I'm doing a STA
WSYNC right before the VSYNC, but this might force me
onto a wrong scannline.
Now, what should I do?
-Remove the STA WSYNC again?
-Try a smaller timer value?
-Do the LDY #$02 before the STA WSYNC?
-Any other idea to grant a stable picture?
And why is Z26 not jerking?
Greetings,
Manuel
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