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31 lines
1.2 KiB
ArmAsm
31 lines
1.2 KiB
ArmAsm
; From http://6502org.wikidot.com/software-delay
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; 25+A cycles (including JSR), 19 bytes (excluding JSR)
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;
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; The branches must not cross page boundaries!
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;
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delay_begin:
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; Cycles Accumulator Carry flag
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; 0 1 2 3 4 5 6 (hex) 0 1 2 3 4 5 6
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; jsr delay_a ; 6 6 6 6 6 6 6 00 01 02 03 04 05 06
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dly0: sbc #7
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delay_a:cmp #7 ; 2 2 2 2 2 2 2 00 01 02 03 04 05 06 0 0 0 0 0 0 0
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bcs dly0 ; 2 2 2 2 2 2 2 00 01 02 03 04 05 06 0 0 0 0 0 0 0
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lsr ; 2 2 2 2 2 2 2 00 00 01 01 02 02 03 0 1 0 1 0 1 0
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bcs dly1 ; 2 3 2 3 2 3 2 00 00 01 01 02 02 03 0 1 0 1 0 1 0
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dly1: beq dly2 ; 3 3 2 2 2 2 2 00 00 01 01 02 02 03 0 1 0 1 0 1 0
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lsr ; 2 2 2 2 2 00 00 01 01 01 1 1 0 0 1
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beq dly3 ; 3 3 2 2 2 00 00 01 01 01 1 1 0 0 1
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bcc dly3 ; 3 3 2 01 01 01 0 0 1
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dly2: bne dly3 ; 2 2 3 00 00 01 0 1 0
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dly3: rts ; 6 6 6 6 6 6 6 00 00 00 00 01 01 01 0 1 1 1 0 0 1
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;
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; Total cycles: 25 26 27 28 29 30 31
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delay_end:
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.assert >delay_begin = >delay_end, error, "delay_a crosses page"
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