In article <340e507e.254358@xxxxxxxxxxxxxxxxxxxxxxx>, you wrote:
>You're gonna hit yourself ;) Look at that last STA VSYNC... you're
>writing $1B to VSYNC. $1B has bit 1 set, so you're leaving VSYNC
>active while the 2600 tries to draw the screen, and that doesn't work.
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DOH!!!!
Aw crap. I hate when I do stupid things like that.
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>I count a maximum of 85 cycles between WSYNCs here. Recall that the
>2600 only has 76 cycles. The screen will end up taking one too many
>scanlines in a few spots (anytime it updates both the playfield and
>player on the same line.)
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Yep. Noticed I'd miscounted last night. Oh well. The code needed to be
cleaned up alot anyways. back to the drawing board. Even though it was
buggy, it was still pretty thrilling to see Bira Bira move around on the
screen. ;)
Incidently, for those of you new to 6502 programming, or (like me) returning
to 6502 programming after more than 15 years, be careful when counting your
instruction cycles. I thought I had plenty to spare because I wasn't paying
attention to the cycle charts in my 6502 handbook, I was going by the
first number I saw in the chart, but the number of cycles an instruction
uses changes depending on your addressing mode.
LDA #$00 takes only 2 cycles.
but
LDA $80,X takes 4!
I won't be burned on that same mistake twice (meaning that I'll probably
be burned on it several more times).
CRACKERS
(Rust on the brain from hell!!!)
--
Accordionist - Wethifl Musician - Atari 2600 Collector | /\/\
*NEW CrAB URL* http://www.hwcn.org/~ad329/crab.html ***| \^^/
Bira Bira Devotee - FES Member - Samurai Pizza Cats Fan| =\/=
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