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31 lines
528 B
NASM
31 lines
528 B
NASM
; The CGB hardware introduces Double Speed Mode.
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; While active, the clock speed is doubled.
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; The hardware can switch between normal speed
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; and double speed at any time, but LCD output
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; collapses during the switch.
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DoubleSpeed:: ; 2fef
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ld hl, rKEY1
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bit 7, [hl]
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jr z, SwitchSpeed
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ret
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; 2ff7
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NormalSpeed:: ; 2ff7
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ld hl, rKEY1
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bit 7, [hl]
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ret z
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; 2ffd
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SwitchSpeed:: ; 2ffd
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set 0, [hl]
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xor a
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ld [rIF], a
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ld [rIE], a
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ld a, $30
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ld [rJOYP], a
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stop ; rgbasm adds a nop after this instruction by default
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ret
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; 300b
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