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Diffstat (limited to 'common/double_speed.asm')
| -rw-r--r-- | common/double_speed.asm | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/common/double_speed.asm b/common/double_speed.asm new file mode 100644 index 000000000..fc1234215 --- /dev/null +++ b/common/double_speed.asm @@ -0,0 +1,31 @@ +; 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: ; 2fef + ld hl, rKEY1 + bit 7, [hl] + jr z, SwitchSpeed + ret +; 2ff7 + +NormalSpeed: ; 2ff7 + ld hl, rKEY1 + bit 7, [hl] + ret z +; 2ffd + +SwitchSpeed: ; 2ffd + set 0, [hl] + xor a + ld [rIF], a + ld [rIE], a + ld a, $30 + ld [rJOYP], a + stop ; rgbasm adds a nop after this instruction by default + ret +; 300b + |