Some reports of screen rolling on the Stella emulator had me stuck, for a
while.
It turns out that the following code was the problem...
ldy #4
lda #D1
Synch sta WSYNC
sta VSYNC ; start vertical synch
dey
bne Synch
sty VSYNC
This code was my 'optimised' beginning of vertical blank/screen stuff.
Here's the non-optimised (ie: working) version....
lda #D1 ; requires D1 already in A
sta WSYNC
sta VSYNC ; start vertical synch
sta WSYNC ; 1st
sta WSYNC ; 2nd TV SYNCH (2 tested OK on PAL, 1
FAILED)
sta WSYNC ; 3rd, to satisfy ES :)
lda #0
sta VSYNC ; stop vertical synch
Now, the first version (appears) to work OK under Z26, and also PCAE. I
believe it works on the real thing, too - though I'm not exactly sure about
that. But definitely causes screen-roll (and super-fast speed) under
Stella.
Looks like the handling of writes to VSYNC is causing the problem - stella
doesn't like multiple writes. I have no idea if my optimised version is
'legal' or not, so I'm junking it, in order to maintain stella-support - but
it's one for people to keep in mind :)
Optimisation of Qb: -105 bytes :)
Cheers
A
--
_ _ _| _ _ _| _ * _ _ ,
(_|| )(_|( (/_\/\/ (_|(_|\/(_(/_ ,~' L_|\
,-' \
see my Museum of Soviet Calculators at ( \
http://www.taswegian.com/MOSCOW/soviet.html \ __ /
L,~' "\__/
@--> v
-
Archives (includes files) at http://www.biglist.com/lists/stella/archives/
Unsub & more at http://www.biglist.com/lists/stella/
