atari2600land's Blog

You swapped #$FF and $D012 from the example I posted. The idea was to not having to load the accumulator for each loop, just do a comparison. Instead of loading a value from a memory address (I/O) and compare it to a fixed value, you can load the value first and compare against the memory address instead. The net effect is only 2 clock cycles (minus first loop) in this case though:

 

loop: LDA $D012 ; 4 cycles
CMP #$FF ; 2 cycles

BNE loop ; 2-3 cycles depending if you cross a page boundary

 

wait: LDA #$FF ; 2 cycles

loop: CMP $D012 ; 4 cycles

BNE loop ; 2-3 cycles

 

Also yes, both in PETSCII and ASCII, the space is 32. Other systems like e.g. the Intellivision has space at 0.

OK, I got that code working now.

I seem to want to have a bunch of little songs, so I was just wondering if there was a way to somehow change the .bin files I use for music. I'm using GoatTracker to make the songs, and it only let me save the values at $3000, $3400, $3800, $3C00 and so on. I bet I could fit my small songs in smaller increments, like $3000, $3200, $3400, $3600 and so on. For example, my death song is only 989 bytes. My title screen song is only 896 bytes, and the level 1 music is only 907 bytes.

Remember that each $100 equals 256 bytes so if the addresses are $400 apart, that is 1024 bytes. But yes, you will be able to merge multiple songs with one player to save quite a bit of space.