I'm new to Atari assembly. I've followed Perihelions tutorials on top of reading Abacus Atari Internals and machine language books. Anyway, in tutorial no8 he explains that the video memory must be on a 256 byte even address, but I dont understand the syntax given in the code.
Why does the last three rows make sure that we are on a 256byte even address? Yea, ds.b reserves 256 bytes of data but it does not align me to an even address? I hope I didnt miss read anything in the tutorial and everything was there right in front of me...
move.l #screen1, d0 ; put screen1 address in d0 clr.b d0 ; put on 256 byte boundary clr.b $ffff820d ; clear STe extra bit lsr.l #8, d0 move.b d0, $ffff8203 ; put in mid screen address byte lsr.w #8, d0 move.b d0, $ffff8201 ; put in high screen address byte section bss ds.b 256 ; 256 byte clear buffer screen ds.b 32000 ; the screen