Emulate AGB audio mixing
@@ -23,6 +23,13 @@ static void refresh_channel(GB_gameboy_t *gb, unsigned index, unsigned cycles_of
static bool is_DAC_enabled(GB_gameboy_t *gb, unsigned index)
{
+ if (gb->model >= GB_MODEL_AGB) {
+ /* On the AGB, mixing is done digitally, so there are no per-channel
+ DACs. Instead, all channels are summed digital regardless of
+ whatever the DAC state would be on a CGB or earlier model. */
+ return true;
+ }
+
switch (index) {
case GB_SQUARE_1:
return gb->io_registers[GB_IO_NR12] & 0xF8;
@@ -37,11 +44,45 @@ static bool is_DAC_enabled(GB_gameboy_t *gb, unsigned index)
return gb->io_registers[GB_IO_NR42] & 0xF8;
}
- return 0;
+ return false;
}
static void update_sample(GB_gameboy_t *gb, unsigned index, int8_t value, unsigned cycles_offset)
{
+ if (gb->model >= GB_MODEL_AGB) {
+ /* On the AGB, because no analog mixing is done, the behavior of NR51 is a bit different.
+ A channel that is not connected to a terminal is idenitcal to a connected channel
+ playing PCM sample 0. */
+ gb->apu.samples[index] = value;
+
+ if (gb->apu_output.sample_rate) {
+ unsigned right_volume = (gb->io_registers[GB_IO_NR50] & 7) + 1;
+ unsigned left_volume = ((gb->io_registers[GB_IO_NR50] >> 4) & 7) + 1;
+
+ GB_sample_t output;
+ if (gb->io_registers[GB_IO_NR51] & (1 << index)) {
+ output.right = (0xf - value * 2) * right_volume;
+ }
+ else {
+ output.right = 0xf * right_volume;
+ }
+
+ if (gb->io_registers[GB_IO_NR51] & (0x10 << index)) {
+ output.left = (0xf - value * 2) * left_volume;
+ }
+ else {
+ output.left = 0xf * left_volume;
+ }
+
+ if (*(uint32_t *)&(gb->apu_output.current_sample[index]) != *(uint32_t *)&output) {
+ refresh_channel(gb, index, cycles_offset);
+ gb->apu_output.current_sample[index] = output;
+ }
+ }
+
+ return;
+ }
+
if (!is_DAC_enabled(gb, index)) {
value = gb->apu.samples[index];
}
@@ -73,6 +114,8 @@ static void render(GB_gameboy_t *gb, bool no_downsampling, GB_sample_t *dest)
UNROLL
for (unsigned i = 0; i < GB_N_CHANNELS; i++) {
double multiplier = CH_STEP;
+
+ if (gb->model < GB_MODEL_AGB) {
if (!is_DAC_enabled(gb, i)) {
gb->apu_output.dac_discharge[i] -= ((double) DAC_DECAY_SPEED) / gb->apu_output.sample_rate;
if (gb->apu_output.dac_discharge[i] < 0) {
@@ -92,6 +135,7 @@ static void render(GB_gameboy_t *gb, bool no_downsampling, GB_sample_t *dest)
multiplier *= gb->apu_output.dac_discharge[i];
}
}
+ }
if (likely(gb->apu_output.last_update[i] == 0 || no_downsampling)) {
output.left += gb->apu_output.current_sample[i].left * multiplier;
