Noise channel support
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Lior Halphon
parent
1a8bcd314d
commit
0e22ad8eb1
148
Core/apu.c
148
Core/apu.c
@ -86,7 +86,7 @@ static void sweep_event(GB_gameboy_t *gb)
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{
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gb->apu.square_channels[GB_SQUARE_1].sample_length = new_sweep_frequency(gb);
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/* Overflow checking only occurs after a delay */
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gb->apu.square_sweep_stop_countdown = 0x13 - gb->apu.square_carry;
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gb->apu.square_sweep_stop_countdown = 0x13 - gb->apu.lf_div;
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gb->apu.square_channels[GB_SQUARE_1].sample_length &= 0x7FF;
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gb->apu.square_sweep_countdown = ((gb->io_registers[GB_IO_NR10] >> 4) & 7);
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@ -140,6 +140,36 @@ void GB_apu_div_event(GB_gameboy_t *gb)
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}
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}
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}
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if (gb->apu.noise_channel.length_enabled) {
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if (gb->apu.noise_channel.pulse_length) {
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if (!--gb->apu.noise_channel.pulse_length) {
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gb->apu.is_active[GB_NOISE] = false;
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update_sample(gb, GB_NOISE, 0, 0);
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}
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}
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}
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uint8_t nr42 = gb->io_registers[GB_IO_NR42];
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if (gb->apu.noise_channel.volume_countdown) {
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if (!--gb->apu.noise_channel.volume_countdown) {
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if ((nr42 & 8) && gb->apu.noise_channel.current_volume < 0xF) {
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gb->apu.noise_channel.current_volume++;
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}
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else if (!(nr42 & 8) && gb->apu.noise_channel.current_volume > 0) {
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gb->apu.noise_channel.current_volume--;
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}
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gb->apu.noise_channel.volume_countdown = (nr42 & 7) * 4;
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update_sample(gb, GB_NOISE,
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(gb->apu.noise_channel.lfsr & 1) ?
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gb->apu.noise_channel.current_volume : 0,
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0);
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}
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}
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}
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if ((gb->apu.div_divider & 3) == 3) {
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@ -158,8 +188,9 @@ void GB_apu_run(GB_gameboy_t *gb)
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uint8_t cycles = gb->apu.apu_cycles >> 1;
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gb->apu.apu_cycles = 0;
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if (!cycles) return;
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/* To align the square signal to 1MHz */
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gb->apu.square_carry ^= cycles & 1;
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gb->apu.lf_div ^= cycles & 1;
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if (gb->apu.square_sweep_stop_countdown) {
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if (gb->apu.square_sweep_stop_countdown > cycles) {
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@ -219,6 +250,36 @@ void GB_apu_run(GB_gameboy_t *gb)
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}
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}
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if (gb->apu.is_active[GB_NOISE]) {
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uint8_t cycles_left = cycles;
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while (unlikely(cycles_left > gb->apu.noise_channel.sample_countdown)) {
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cycles_left -= gb->apu.noise_channel.sample_countdown + 1;
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gb->apu.noise_channel.sample_countdown = gb->apu.noise_channel.sample_length * 2 + 1;
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/* Step LFSR */
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unsigned high_bit_mask = gb->apu.noise_channel.narrow ? 0x4040 : 0x4000;
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// This formula is different on a GBA!
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bool new_high_bit = (gb->apu.noise_channel.lfsr ^ (gb->apu.noise_channel.lfsr >> 1) ^ 1) & 1;
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gb->apu.noise_channel.lfsr >>= 1;
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if (new_high_bit) {
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gb->apu.noise_channel.lfsr |= high_bit_mask;
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}
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else {
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/* This code is not redundent, it's relevant when switching LFSR widths */
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gb->apu.noise_channel.lfsr &= ~high_bit_mask;
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}
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update_sample(gb, GB_NOISE,
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(gb->apu.noise_channel.lfsr & 1) ?
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gb->apu.noise_channel.current_volume : 0,
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0);
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}
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if (cycles_left) {
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gb->apu.noise_channel.sample_countdown -= cycles_left;
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}
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}
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if (gb->apu_output.sample_rate) {
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gb->apu_output.cycles_since_render += cycles;
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double cycles_per_sample = CPU_FREQUENCY / (double)gb->apu_output.sample_rate; // TODO: this should be cached!
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@ -267,7 +328,8 @@ void GB_apu_init(GB_gameboy_t *gb)
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for (int i = 0; i < 4; i++) {
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gb->apu.left_enabled[i] = gb->apu.right_enabled[i] = true;
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}
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gb->apu.square_carry = 1;
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gb->apu.lf_div = 1;
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gb->apu.noise_channel.sample_length = 1;
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}
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uint8_t GB_apu_read(GB_gameboy_t *gb, uint8_t reg)
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@ -350,6 +412,7 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
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}
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break;
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/* Square channels */
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case GB_IO_NR10:
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gb->apu.square_sweep_countdown = ((value >> 4) & 7);
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break;
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@ -382,7 +445,6 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
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break;
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}
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/* Square channels */
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case GB_IO_NR14:
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case GB_IO_NR24: {
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unsigned index = reg == GB_IO_NR24? GB_SQUARE_2: GB_SQUARE_1;
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@ -392,17 +454,17 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
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gb->apu.square_channels[index].current_sample_index = 7;
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if (!gb->apu.is_active[index]) {
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gb->apu.square_channels[index].sample_countdown = (gb->apu.square_channels[index].sample_length ^ 0x7FF) * 2 + 6 - gb->apu.square_carry;
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gb->apu.square_channels[index].sample_countdown = (gb->apu.square_channels[index].sample_length ^ 0x7FF) * 2 + 6 - gb->apu.lf_div;
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}
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else {
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/* Timing quirk: if already active, sound starts 2 (2MHz) ticks earlier.
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if both active AND already emitted a sample, sound starts the next 1MHz tick,
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and one sample is skipped */
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if (!gb->apu.square_channels[index].sample_emitted) {
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gb->apu.square_channels[index].sample_countdown = (gb->apu.square_channels[index].sample_length ^ 0x7FF) * 2 + 4 - gb->apu.square_carry;
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gb->apu.square_channels[index].sample_countdown = (gb->apu.square_channels[index].sample_length ^ 0x7FF) * 2 + 4 - gb->apu.lf_div;
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}
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else {
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gb->apu.square_channels[index].sample_countdown = gb->apu.square_carry;
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gb->apu.square_channels[index].sample_countdown = gb->apu.lf_div;
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gb->apu.square_channels[index].current_sample_index = 0;
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}
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}
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@ -419,7 +481,7 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
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if (index == GB_SQUARE_1 && gb->io_registers[GB_IO_NR10] & 7) {
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/* APU bug: if shift is nonzero, overflow check also occurs on trigger */
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gb->apu.square_sweep_stop_countdown = 0x13 - gb->apu.square_carry;
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gb->apu.square_sweep_stop_countdown = 0x13 - gb->apu.lf_div;
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}
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/* Note that we don't change the sample just yet! This was verified on hardware. */
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@ -524,6 +586,76 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
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break;
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/* Noise Channel */
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case GB_IO_NR41: {
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gb->apu.noise_channel.pulse_length = (0x40 - (value & 0x3f));
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break;
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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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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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break;
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}
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case GB_IO_NR43: {
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gb->apu.noise_channel.narrow = value & 8;
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unsigned divisor = (value & 0x07) << 2;
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if (!divisor) divisor = 2;
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gb->apu.noise_channel.sample_length = (divisor << (value >> 4)) - 1;
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break;
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}
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case GB_IO_NR44: {
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if (value & 0x80) {
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gb->apu.noise_channel.lfsr = 0;
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gb->apu.noise_channel.sample_countdown = (gb->apu.noise_channel.sample_length) * 2 + 4 - gb->apu.lf_div;
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if (gb->apu.is_active[GB_NOISE]) {
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gb->apu.noise_channel.sample_countdown += 2;
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}
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gb->apu.noise_channel.current_volume = gb->io_registers[GB_IO_NR42] >> 4;
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gb->apu.noise_channel.volume_countdown = (gb->io_registers[GB_IO_NR42] & 7) * 4;
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if ((gb->io_registers[GB_IO_NR42] & 0xF8) != 0) {
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gb->apu.is_active[GB_NOISE] = true;
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}
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if (gb->apu.noise_channel.pulse_length == 0) {
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gb->apu.noise_channel.pulse_length = 0x40;
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gb->apu.noise_channel.length_enabled = false;
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}
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/* Note that we don't change the sample just yet! This was verified on hardware. */
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}
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/* APU glitch - if length is enabled while the DIV-divider's LSB is 1, tick the length once. */
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if ((value & 0x40) &&
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!gb->apu.noise_channel.length_enabled &&
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(gb->apu.div_divider & 1) &&
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gb->apu.noise_channel.pulse_length) {
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gb->apu.noise_channel.pulse_length--;
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if (gb->apu.noise_channel.pulse_length == 0) {
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if (value & 0x80) {
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gb->apu.noise_channel.pulse_length = 0x3F;
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}
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else {
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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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}
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}
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gb->apu.noise_channel.length_enabled = value & 0x40;
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break;
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}
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default:
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if (reg >= GB_IO_WAV_START && reg <= GB_IO_WAV_END) {
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gb->apu.wave_channel.wave_form[(reg - GB_IO_WAV_START) * 2] = value >> 4;
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18
Core/apu.h
18
Core/apu.h
@ -40,8 +40,8 @@ typedef struct
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uint8_t div_divider; // The DIV register ticks the APU at 512Hz, but is then divided
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// once more to generate 128Hz and 64Hz clocks
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uint8_t square_carry; // The square channels tick at 1MHz instead of 2,
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// so we need a carry to divide the signal
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uint8_t lf_div; // The APU runs in 2MHz, but channels 1, 2 and 4 run in 1MHZ so we divide
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// need to divide the signal.
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uint8_t square_sweep_countdown; // In 128Hz
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uint8_t square_sweep_stop_countdown; // In 2 MHz
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@ -73,6 +73,20 @@ typedef struct
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int8_t wave_form[32];
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bool wave_form_just_read;
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} wave_channel;
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struct {
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uint16_t pulse_length; // Reloaded from NR41 (xorred), in 256Hz DIV ticks
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uint8_t current_volume; // Reloaded from NR42
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uint8_t volume_countdown; // Reloaded from NR42
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uint16_t lfsr;
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bool narrow;
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uint16_t sample_countdown; // in APU ticks (Reloaded from sample_length)
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uint16_t sample_length; // From NR43, in APU ticks
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bool length_enabled; // NR44
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} noise_channel;
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} GB_apu_t;
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typedef struct {
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