Erik Mooney wrote:
> The standard routine (don't think there IS any other, since the standard
> does it with no cycles to spare) uses the 12 bytes for the pointers plus
> one for temp storage. You can store the score data any way you like and
> set up the pointers during vblank. I'd probably recommend 3 bytes of BCD.
I just checked it - I was using a STA WSYNC in there, and added up
the cycles including it - 76 :) So, I pulled it out, synced things
up ahead of time, and put a useless BIT $00 in its place, just so
I can gloat ;) 3 cycles free - don't know what I could do with them
though. Sounds like there are very very few variations to this...
it'd be interesting if I have discovered one, by recreating the wheel.
The other way of doing this (and it's how I would be doing it on the
C64) is dropping the LDA ($xx),y thing and use self-modifying code
in zero page... the loads would only take 4 cycles then, and you
could avoid at least one TAX as well, by using LDX $XXXX,y - 3 cycles
saved right there - perhaps 10? (just a guess) cycles could be free
per line. Perhaps I'll work on this next.
Two things that make the Atari 2600 easier to work with than the C64:
1) No need to get "a stable raster" - it's built right into the 2600
with WSYNC.
2) No DMA stopping the processor for graphic fetches.
I'm finding this extremely fun at the moment.
--
Robin Harbron macbeth@xxxxxxxxxxx
http://www.tbaytel.net/macbeth
--
Archives (includes files) at http://www.biglist.com/lists/stella/archives/
Unsub & more at http://www.biglist.com/lists/stella/stella.html
Don't post pirate BINs to Stellalist. Be a programmer, not a pirate.
Write the best game, win framed autographs of famous Atari alumni!!
