Subject: Re: [stella] 6 digit score display and other ramblings From: emooney@xxxxxxxxxxxxxxxx (Erik Mooney) Date: Wed, 18 Mar 1998 02:08:42 GMT |
> LDA COUNT ; WAIT CYCLES = 16 - COUNT > LSR A ; SETUP CARRY BIT > STA JUMP+1 ; SELF MODIFYING...CHANGES JUMP VALUE > ; (not sure how to convey this) > LDX #1 ; SETUP X FOR OPTIONAL LOOP ; SETUP Z FLAG > >DELAY STA WSYNC > BCC JUMP ; WASTE 2 OR 3 CYCLES >JUMP BNE END ; WASTE 3 CYCLES ; DEFAULT IS 5 CYCLES TOTAL > NOP ; WASTE 2 CYCLES > NOP ; WASTE 2 CYCLES > NOP ; WASTE 2 CYCLES > NOP ; WASTE 2 CYCLES > NOP ; WASTE 2 CYCLES >END ... > >This should give you a delay between 5 and 16 cycles after the WSYNC. >You can add more NOP's or a delay loop to get longer delays. Actually, looking at my 6502 docs again, doesn't JMP support absolute indirect addressing? ie, if I store #$10 in memory location $80, and #$F6 in location $81, the instruction JMP ($80) will jump to $F610. Trying it in the PC Atari debugger, the addressing mode does exist... so it should be possible to get single-cycle-precision delay in ROM, without self-modifiying code. -- 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!!
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