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Atari coding BBS
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Posted by: damog
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Dec,20.2012-21:20
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hello folks!
inspired by the amazing releases from SILLIVENTURE! i thought i'd crack out the old Devpac :)
i wish i could say it's all flooding back to me but alas, it isnt :D
there's one thing i'm really confused about I was hoping someone could help with.. I dug out some startup code (courtesy of Mr Pink) and i'm fucked if I can work out why the good old 'cpu time left' palette trick isn't working.
Instead of giving me a solid block of colour indicating how much of the vbl I have left, i'm getting an effect that suggests the code isn't waiting for a vbl.
https://dl.dropbox.com/u/3791755/vbl.png
the way it checks for the vbl is such:
;-------------------------------------------------------------------------;
screen_swap:
move.l screen0,d0
move.l screen1,d1
move.l d0,screen1
move.l d1,screen0
lsr.w #8,d0
move.l d0,$ffff8200.w
move.w #$700,$ffff8240.w
.skip
bsr waitvbl
move.w #0,$ffff8240.w
rts
;-------------------------------------------------------------------------;
waitvbl:
move.l d0,-(a7)
move.l $468.w,d0
.wait:
cmp.w $468.w,d0
beq.s .wait
move.l (a7)+,d0
rts
;-----------------------
my logic dictates that $468 -must- be changing, otherwise the waitloop would hang, I even tried installing a custom vbl that changed $468, but alas, the same result.
this is BASIC (well not literally, i can do this in STOS!!!) so I'm flummoxed!!
can anyone explain why it's not working, please :D
xx
damo
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