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Emulation of NRX2-write glitches. Fixes Prehistorik Man audio.

This commit is contained in:
Lior Halphon 2017-09-29 01:19:48 +03:00
parent 78446f0ed4
commit d9b0576351
1 changed files with 54 additions and 22 deletions
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76
Core/apu.c
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@ -115,6 +115,41 @@ static uint16_t new_sweep_sample_legnth(GB_gameboy_t *gb)
return gb->apu.shadow_sweep_sample_legnth + delta;
}
static void update_square_sample(GB_gameboy_t *gb, unsigned index)
{
uint8_t duty = gb->io_registers[index == GB_SQUARE_1? GB_IO_NR11 :GB_IO_NR21] >> 6;
update_sample(gb, index,
duties[gb->apu.square_channels[index].current_sample_index + duty * 8]?
gb->apu.square_channels[index].current_volume : 0,
0);
}
/* the effects of NRX2 writes on current volume are not well documented and differ
between models and variants. The exact behavior can only be verified on CGB as it
requires the PCM12 register. The behavior implemented here was verified on *my*
CGB, which might behave differently from other CGB revisions, as well as from the
DMG, MGB or SGB/2 */
static void nrx2_glitch(uint8_t *volume, uint8_t value, uint8_t old_value)
{
if (value & 8) {
(*volume)++;
}
if (((value ^ old_value) & 8)) {
*volume = 0x10 - *volume;
}
if ((value & 7) && !(old_value & 7) && *volume && !(value & 8)) {
(*volume)--;
}
if ((old_value & 7) && (value & 8)) {
(*volume)--;
}
(*volume) &= 0xF;
}
void GB_apu_div_event(GB_gameboy_t *gb)
{
if (!gb->apu.global_enable) return;
@ -136,11 +171,7 @@ void GB_apu_div_event(GB_gameboy_t *gb)
gb->apu.square_channels[i].volume_countdown = nrx2 & 7;
uint8_t duty = gb->io_registers[i == GB_SQUARE_1? GB_IO_NR11 :GB_IO_NR21] >> 6;
update_sample(gb, i,
duties[gb->apu.square_channels[i].current_sample_index + duty * 8]?
gb->apu.square_channels[i].current_volume : 0,
0);
update_square_sample(gb, i);
}
}
}
@ -261,12 +292,7 @@ void GB_apu_run(GB_gameboy_t *gb)
gb->apu.square_channels[i].current_sample_index++;
gb->apu.square_channels[i].current_sample_index &= 0x7;
uint8_t duty = gb->io_registers[i == GB_SQUARE_1? GB_IO_NR11 :GB_IO_NR21] >> 6;
update_sample(gb, i,
duties[gb->apu.square_channels[i].current_sample_index + duty * 8]?
gb->apu.square_channels[i].current_volume : 0,
cycles - cycles_left);
update_square_sample(gb, i);
}
if (cycles_left) {
gb->apu.square_channels[i].sample_countdown -= cycles_left;
@ -432,8 +458,7 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
reg = GB_IO_WAV_START + gb->apu.wave_channel.current_sample_index / 2;
}
gb->io_registers[reg] = value;
/* Todo: this can and should be rewritten with a function table. */
switch (reg) {
/* Globals */
case GB_IO_NR50:
@ -479,13 +504,13 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
/* Square channels */
case GB_IO_NR10:
if (gb->apu.sweep_decreasing && !(gb->io_registers[GB_IO_NR10] & 8)) {
if (gb->apu.sweep_decreasing && !(value & 8)) {
gb->apu.is_active[GB_SQUARE_1] = false;
update_sample(gb, GB_SQUARE_1, 0, 0);
gb->apu.sweep_enabled = false;
gb->apu.square_sweep_calculate_countdown = 0;
}
if ((gb->io_registers[GB_IO_NR10] & 0x70) == 0) {
if ((value & 0x70) == 0) {
/* Todo: what happens if we set period to 0 while a calculate event is scheduled, and then
re-set it to non-zero? */
gb->apu.square_sweep_calculate_countdown = 0;
@ -504,14 +529,18 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
case GB_IO_NR12:
case GB_IO_NR22: {
/* TODO: What happens when changing bits 0-2 after triggering? */
unsigned index = reg == GB_IO_NR22? GB_SQUARE_2: GB_SQUARE_1;
if ((value & 0xF8) == 0) {
/* According to Blargg's test ROM this should disable the channel instantly
TODO: verify how "instant" the change is using PCM12*/
unsigned index = reg == GB_IO_NR22? GB_SQUARE_2: GB_SQUARE_1;
TODO: verify how "instant" the change is using PCM12 */
update_sample(gb, index, 0, 0);
gb->apu.is_active[index] = false;
}
else if (gb->apu.is_active[index]) {
nrx2_glitch(&gb->apu.square_channels[index].current_volume, value, gb->io_registers[reg]);
update_square_sample(gb, index);
}
break;
}
@ -678,13 +707,17 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
}
case GB_IO_NR42: {
/* TODO: What happens when changing bits 0-2 after triggering? */
if ((value & 0xF8) == 0) {
/* According to Blargg's test ROM this should disable the channel instantly
TODO: verify how "instant" the change is using PCM34 */
TODO: verify how "instant" the change is using PCM12 */
update_sample(gb, GB_NOISE, 0, 0);
gb->apu.is_active[GB_NOISE] = false;
}
else if (gb->apu.is_active[GB_NOISE]){
nrx2_glitch(&gb->apu.noise_channel.current_volume, value, gb->io_registers[reg]);
update_square_sample(gb, GB_NOISE);
}
break;
}
@ -762,8 +795,7 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
gb->apu.wave_channel.wave_form[(reg - GB_IO_WAV_START) * 2 + 1] = value & 0xF;
}
}
gb->io_registers[reg] = value;
}
size_t GB_apu_get_current_buffer_length(GB_gameboy_t *gb)