From ac418b9de18765cdd8c0e94d7df46d5ca0820f0f Mon Sep 17 00:00:00 2001 From: Lior Halphon Date: Mon, 30 Sep 2019 00:09:25 +0300 Subject: [PATCH] Pass channel_1_freq_change_timing --- Core/apu.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/Core/apu.c b/Core/apu.c index ee58138..a6247ec 100644 --- a/Core/apu.c +++ b/Core/apu.c @@ -681,6 +681,21 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value) case GB_IO_NR14: case GB_IO_NR24: { unsigned index = reg == GB_IO_NR24? GB_SQUARE_2: GB_SQUARE_1; + + /* TODO: When the sample length changes right before being updated, the countdown should change to the + old length, but the current sample should not change. Because our write timing isn't accurate to + the T-cycle, we hack around it by stepping the sample index backwards. */ + if ((value & 0x80) == 0 && gb->apu.is_active[index]) { + /* On an AGB, as well as on CGB C and earlier (TODO: Tested: 0, B and C), it behaves slightly different on + double speed. */ + if (gb->model == GB_MODEL_CGB_E /* || gb->model == GB_MODEL_CGB_D */ || gb->apu.square_channels[index].sample_countdown & 1) { + if (gb->apu.square_channels[index].sample_countdown >> 1 == (gb->apu.square_channels[index].sample_length ^ 0x7FF)) { + gb->apu.square_channels[index].current_sample_index--; + gb->apu.square_channels[index].current_sample_index &= 7; + } + } + } + gb->apu.square_channels[index].sample_length &= 0xFF; gb->apu.square_channels[index].sample_length |= (value & 7) << 8; if (index == GB_SQUARE_1) {