Stereo sound support in SGU-1 and Emu

Author: smokku

src/chips/sgu1.cc

@@ -35,7 +35,7 @@ void sgu1_init(sgu1_t* sgu, const sgu1_desc_t* desc) {
     sgu->sample_period = (desc->tick_hz * SGU1_FIXEDPOINT_SCALE) / desc->sound_hz;
     sgu->sample_counter = sgu->sample_period;
     sgu->sample_mag = desc->magnitude;
-    sgu->sample_accum_count = 1.0f;
+    sgu->sample_accum_count[0] = sgu->sample_accum_count[1] = 1.0f;
     sgu->su = new SoundUnit();
     sgu->tick_period = (desc->tick_hz * SGU1_FIXEDPOINT_SCALE) / (CHIP_CLOCK / CHIP_DIVIDER);
     sgu->tick_counter = sgu->tick_period;
@@ -48,9 +48,9 @@ void sgu1_reset(sgu1_t* sgu) {
     memset(sgu->reg, 0, sizeof(sgu->reg));
     sgu->tick_counter = sgu->tick_period;
     sgu->sample_counter = sgu->sample_period;
-    sgu->sample = 0.0f;
-    sgu->sample_accum = 0.0f;
-    sgu->sample_accum_count = 1.0f;
+    sgu->sample[0] = sgu->sample[1] = 0.0f;
+    sgu->sample_accum[0] = sgu->sample_accum[1] = 0.0f;
+    sgu->sample_accum_count[0] = sgu->sample_accum_count[1] = 1.0f;
     sgu->pins = 0;
 }
 
@@ -62,9 +62,10 @@ static uint64_t _sgu1_tick(sgu1_t* sgu, uint64_t pins) {
         sgu->tick_counter += sgu->tick_period;
         short l, r;
         SGU_SU->NextSample(&l, &r);
-        int sample = ((int)l + (int)r) >> 1;
-        sgu->sample_accum += ((float)sample / 32767.0f);
-        sgu->sample_accum_count += 1.0f;
+        sgu->sample_accum[0] += ((float)l / 32767.0f);
+        sgu->sample_accum_count[0] += 1.0f;
+        sgu->sample_accum[1] += ((float)r / 32767.0f);
+        sgu->sample_accum_count[1] += 1.0f;
 
         for (int i = 0; i < SGU1_NUM_CHANNELS; i++) {
             sgu->voice[i].sample_buffer[sgu->voice[i].sample_pos++] = (float)SGU_SU->GetSample(i);
@@ -78,10 +79,12 @@ static uint64_t _sgu1_tick(sgu1_t* sgu, uint64_t pins) {
     sgu->sample_counter -= SGU1_FIXEDPOINT_SCALE;
     if (sgu->sample_counter <= 0) {
         sgu->sample_counter += sgu->sample_period;
-        float s = sgu->sample_accum / sgu->sample_accum_count;
-        sgu->sample = sgu->sample_mag * s;
-        sgu->sample_accum = 0.0f;
-        sgu->sample_accum_count = 0.0f;
+        float l = sgu->sample_accum[0] / sgu->sample_accum_count[0];
+        sgu->sample[0] = sgu->sample_mag * l;
+        float r = sgu->sample_accum[1] / sgu->sample_accum_count[1];
+        sgu->sample[1] = sgu->sample_mag * r;
+        sgu->sample_accum[0] = sgu->sample_accum[1] = 0.0f;
+        sgu->sample_accum_count[0] = sgu->sample_accum_count[1] = 0.0f;
         pins |= SGU1_SAMPLE;
     }
     else {

src/chips/sgu1.h

@@ -183,10 +183,10 @@ typedef struct {
     // sample generation state
     int sample_period;
     int sample_counter;
-    float sample_accum;
-    float sample_accum_count;
     float sample_mag;
-    float sample;
+    float sample_accum[2];
+    float sample_accum_count[2];
+    float sample[2];  // Left, Right
     // voice visualization
     struct {
         int sample_pos;

src/systems/x65.c

@@ -37,7 +37,7 @@ void x65_init(x65_t* sys, const x65_desc_t* desc) {
     sys->joystick_type = desc->joystick_type;
     sys->debug = desc->debug;
     sys->audio.callback = desc->audio.callback;
-    sys->audio.num_samples = _X65_DEFAULT(desc->audio.num_samples, X65_DEFAULT_AUDIO_SAMPLES);
+    sys->audio.num_samples = _X65_DEFAULT(desc->audio.num_samples, X65_DEFAULT_AUDIO_SAMPLES) * X65_AUDIO_CHANNELS;
     CHIPS_ASSERT(sys->audio.num_samples <= X65_MAX_AUDIO_SAMPLES);
 
     // initialize the hardware
@@ -225,7 +225,8 @@ static uint64_t _x65_tick(x65_t* sys, uint64_t pins) {
         sgu_pins = sgu1_tick(&sys->sgu, sgu_pins);
         if (sgu_pins & SGU1_SAMPLE) {
             // new audio sample ready
-            sys->audio.sample_buffer[sys->audio.sample_pos++] = sys->sgu.sample;
+            sys->audio.sample_buffer[sys->audio.sample_pos++] = sys->sgu.sample[0];
+            sys->audio.sample_buffer[sys->audio.sample_pos++] = sys->sgu.sample[1];
             if (sys->audio.sample_pos == sys->audio.num_samples) {
                 if (sys->audio.callback.func) {
                     sys->audio.callback.func(

src/systems/x65.h

@@ -50,6 +50,7 @@ extern "C" {
 #define X65_FREQUENCY             (1826300)  // clock frequency in Hz
 #define X65_MAX_AUDIO_SAMPLES     (1024)     // max number of audio samples in internal sample buffer
 #define X65_DEFAULT_AUDIO_SAMPLES (128)      // default number of samples in internal sample buffer
+#define X65_AUDIO_CHANNELS        (2)        // stereo output
 
 // X65 joystick types
 typedef enum {

src/x65.c

@@ -109,7 +109,7 @@ static void* labels = NULL;
 // audio-streaming callback
 static void push_audio(const float* samples, int num_samples, void* user_data) {
     (void)user_data;
-    saudio_push(samples, num_samples);
+    saudio_push(samples, num_samples / X65_AUDIO_CHANNELS);
 }
 
 // get x65_desc_t struct based on joystick type
@@ -147,6 +147,7 @@ static void app_load_rom_labels(const char* rom_file) {
 
 void app_init(void) {
     saudio_setup(&(saudio_desc){
+        .num_channels = X65_AUDIO_CHANNELS,
         .logger.func = slog_func,
     });
     x65_joystick_type_t joy_type = arguments.joy ? X65_JOYSTICKTYPE_DIGITAL_1 : X65_JOYSTICKTYPE_NONE;