shithub: pokecrystal

ref: d9d688df4e4cdce07991856b13e9cf579de45bd4
dir: /home/double_speed.asm/

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; The CGB hardware introduces Double Speed Mode.
; While active, the clock speed is doubled.

; The hardware can switch between normal speed
; and double speed at any time, but LCD output
; collapses during the switch.

DoubleSpeed::
	ld hl, rKEY1
	bit 7, [hl]
	jr z, SwitchSpeed
	ret

NormalSpeed::
	ld hl, rKEY1
	bit 7, [hl]
	ret z

SwitchSpeed::
	set 0, [hl]
	xor a
	ldh [rIF], a
	ldh [rIE], a
	ld a, $30
	ldh [rJOYP], a
	stop ; rgbasm adds a nop after this instruction by default
	ret