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