>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 $00 in its place, just so
>I can gloat ;) 3 cycles free - don't know what I could do with them
>though. Sounds like there are very very few variations to this...
>it'd be interesting if I have discovered one, by recreating the wheel.
Um, that shouldn't have worked. If you had 73 cycles plus the WSYNC, it
shouldn't have looked right. STA WSYNC actually takes five cycles - it
will not catch the end of the current line if the STA WSYNC begins on cycle
73 or later (if its last cycle is 75 or 76.) I think this is because the
WSYNC signal is high during cycles 75 and 76 - during this time, the
electron beam is physically moving back to the left side of the screen -
and the instruction looks for the leading edge of the WSYNC, then restarts
the processor on the trailing edge to match what the TV hardware is doing.
(help, someone more hardware-inclined?)
>The other way of doing this (and it's how I would be doing it on the
>C64) is dropping the LDA ($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 $XXXX,y - 3 cycles
>saved right there - perhaps 10? (just a guess) cycles could be free
>per line. Perhaps I'll work on this next.
Er, huh? Wouldn't you still need to go through the LDA ($xx),y thing, then
write that number into the zeropage code for each scanline? There
certainly isn't enough memory to hold an unrolled loop... maybe on the
Supercharger...
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