diff options
Diffstat (limited to 'src/boot.asm')
| -rw-r--r-- | src/boot.asm | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/src/boot.asm b/src/boot.asm index 88eb240..f649008 100644 --- a/src/boot.asm +++ b/src/boot.asm @@ -44,6 +44,20 @@ KernelInit: push af ; boot ROM hands the console model in A/B - push bc ; park it on the (uncleared) stack for dmesg + ; CGB double-speed mode: 8.4 MHz for the whole kernel + userland. The + ; PPU/LCD keep their normal rate; the timer and DIV double with the CPU, + ; which TimerISR (128 Hz -> 64 Hz toggle) and sys_sleep (DIV halving) + ; compensate for. P1 select lines off first, per the hardware procedure. + ldh a, [$FF4D] ; KEY1 + bit 7, a ; already fast? (warm reboot) + jr nz, .fast + ld a, $30 + ldh [$FF00], a ; P1: no select lines (STOP quirk guard) + ld a, 1 + ldh [$FF4D], a ; KEY1.0 = prepare speed switch + stop ; switch: continues in double speed +.fast + ; enable cart RAM (MBC5) ld a, $0A ld [MBC5_RAM_ENABLE], a |