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Emulation of a newly discovered revision specific APU quirk

This commit is contained in:
Lior Halphon 2021-01-03 13:49:36 +02:00
parent ecace40fb0
commit f9b13c66b1
1 changed files with 15 additions and 5 deletions
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20
Core/apu.c
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@ -836,6 +836,7 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
}
}
uint16_t old_sample_length = gb->apu.square_channels[index].sample_length;
gb->apu.square_channels[index].sample_length &= 0xFF;
gb->apu.square_channels[index].sample_length |= (value & 7) << 8;
if (value & 0x80) {
@ -845,12 +846,21 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
gb->apu.square_channels[index].sample_countdown = (gb->apu.square_channels[index].sample_length ^ 0x7FF) * 2 + 6 - gb->apu.lf_div;
}
else {
/* Timing quirk: if already active, sound starts 2 (2MHz) ticks earlier.*/
if (gb->apu.square_channels[index].sample_countdown <= 1) {
gb->apu.square_channels[index].current_sample_index++;
gb->apu.square_channels[index].current_sample_index &= 0x7;
unsigned extra_delay = 0;
if (gb->model == GB_MODEL_CGB_E /* || gb->model == GB_MODEL_CGB_D */) {
if ((!(value & 4) && ((gb->io_registers[reg] & 4) || old_sample_length == 0x3FF)) ||
(old_sample_length == 0x7FF && gb->apu.square_channels[index].sample_length != 0x7FF)) {
gb->apu.square_channels[index].current_sample_index++;
gb->apu.square_channels[index].current_sample_index &= 0x7;
}
else if (gb->apu.square_channels[index].sample_length == 0x7FF &&
old_sample_length != 0x7FF &&
(gb->apu.square_channels[index].current_sample_index & 0x80)) {
extra_delay += 2;
}
}
gb->apu.square_channels[index].sample_countdown = (gb->apu.square_channels[index].sample_length ^ 0x7FF) * 2 + 4 - gb->apu.lf_div;
/* Timing quirk: if already active, sound starts 2 (2MHz) ticks earlier.*/
gb->apu.square_channels[index].sample_countdown = (gb->apu.square_channels[index].sample_length ^ 0x7FF) * 2 + 4 - gb->apu.lf_div + extra_delay;
}
gb->apu.square_channels[index].current_volume = gb->io_registers[index == GB_SQUARE_1 ? GB_IO_NR12 : GB_IO_NR22] >> 4;