remove aica frame skipping, unnecessary being that we're timing based on the aica buffer state, not the host's buffer (#2)

give ta a fixed amount of time to render each frame until a better heuristic is figured out

src/audio/soundio_backend.c

@@ -9,7 +9,7 @@ struct audio_backend {
   struct SoundIo *soundio;
   struct SoundIoDevice *device;
   struct SoundIoOutStream *outstream;
-  int frames_silenced;
+  uint32_t frames[AICA_SAMPLE_FREQ];
 };
 
 static void audio_write_callback(struct SoundIoOutStream *outstream,
@@ -19,21 +19,10 @@ static void audio_write_callback(struct SoundIoOutStream *outstream,
   struct SoundIoChannelArea *areas;
   int err;
 
-  /* if any frames were silenced previously in order to prevent an underflow,
-     discard the same number of incoming aica frames to keep the audio time
-     domain in sync with the emulator */
-  while (audio->frames_silenced) {
-    int skipped = aica_skip_frames(audio->aica, audio->frames_silenced);
-    if (!skipped) {
-      break;
-    }
-    audio->frames_silenced -= skipped;
-  }
-
-  uint32_t frames[10];
-  int16_t *samples = (int16_t *)frames;
-  int frames_remaining = frame_count_max;
+  int16_t *samples = (int16_t *)audio->frames;
   int frames_available = aica_available_frames(audio->aica);
+  int frames_silence = frame_count_max - frames_available;
+  int frames_remaining = frames_available + frames_silence;
 
   while (frames_remaining > 0) {
     int frame_count = frames_remaining;
@@ -49,16 +38,15 @@ static void audio_write_callback(struct SoundIoOutStream *outstream,
     }
 
     for (int frame = 0; frame < frame_count;) {
-      int n = MIN(frame_count - frame, array_size(frames));
+      int n = MIN(frame_count - frame, array_size(audio->frames));
 
       if (frames_available > 0) {
         /* batch read frames from aica */
-        n = aica_read_frames(audio->aica, frames, n);
+        n = aica_read_frames(audio->aica, audio->frames, n);
         frames_available -= n;
       } else {
         /* write out silence */
-        memset(frames, 0, sizeof(frames));
-        audio->frames_silenced += n;
+        memset(audio->frames, 0, n * 4);
       }
 
       /* copy frames to output stream */
@@ -92,7 +80,7 @@ void audio_pump_events(struct audio_backend *audio) {
 }
 
 int audio_buffer_low(struct audio_backend *audio) {
-  int low_water_mark = (int)(44100.0f * (OPTION_latency / 1000.0f));
+  int low_water_mark = (int)((float)AICA_SAMPLE_FREQ * (OPTION_latency / 1000.0f));
   return aica_available_frames(audio->aica) <= low_water_mark;
 }
 
@@ -163,7 +151,7 @@ struct audio_backend *audio_create(struct aica *aica) {
   {
     audio->outstream = soundio_outstream_create(audio->device);
     audio->outstream->format = SoundIoFormatS16NE;
-    audio->outstream->sample_rate = 44100;
+    audio->outstream->sample_rate = AICA_SAMPLE_FREQ;
     audio->outstream->userdata = audio;
     audio->outstream->write_callback = &audio_write_callback;
     audio->outstream->underflow_callback = &audio_underflow_callback;

src/emu/emulator.c

@@ -214,13 +214,13 @@ static void *emu_core_thread(void *data) {
   int64_t next_pump_time = 0;
 
   while (emu->running) {
-    current_time = time_nanoseconds();
-
     while (audio_buffer_low(audio)) {
       dc_tick(emu->dc, MACHINE_STEP);
     }
 
     /* audio events are just for device connections, check infrequently */
+    current_time = time_nanoseconds();
+
     if (current_time > next_pump_time) {
       audio_pump_events(audio);
       next_pump_time = current_time + NS_PER_SEC;

src/hw/aica/aica.c

@@ -22,7 +22,6 @@ DEFINE_AGGREGATE_COUNTER(aica_samples);
 #define LOG_AICA(...)
 #endif
 
-#define AICA_SAMPLE_FREQ 44100
 #define AICA_SAMPLE_BATCH 10
 #define AICA_NUM_CHANNELS 64
 
@@ -391,16 +390,6 @@ static void aica_write_frames(struct aica *aica, const void *frames,
   }
 }
 
-int aica_skip_frames(struct aica *aica, int num_frames) {
-  int available = ringbuf_available(aica->frames);
-  int size = MIN(available, num_frames * 4);
-  CHECK_EQ(size % 4, 0);
-
-  ringbuf_advance_read_ptr(aica->frames, size);
-
-  return size / 4;
-}
-
 int aica_read_frames(struct aica *aica, void *frames, int num_frames) {
   int available = ringbuf_available(aica->frames);
   int size = MIN(available, num_frames * 4);

src/hw/aica/aica.h

@@ -7,6 +7,8 @@
 struct aica;
 struct dreamcast;
 
+#define AICA_SAMPLE_FREQ 44100
+
 AM_DECLARE(aica_reg_map);
 AM_DECLARE(aica_data_map);
 
@@ -14,7 +16,6 @@ struct aica *aica_create(struct dreamcast *dc);
 void aica_destroy(struct aica *aica);
 
 int aica_available_frames(struct aica *aica);
-int aica_skip_frames(struct aica *aica, int num_frames);
 int aica_read_frames(struct aica *aica, void *buffer, int num_frames);
 
 #endif

src/hw/pvr/ta.c

@@ -733,11 +733,9 @@ static void ta_start_render(struct ta *ta, struct tile_ctx *ctx) {
   int num_polys = 0;
   ta_register_texture_sources(ta, ctx, &num_polys);
 
-  /* supposedly, the dreamcast can push around ~3 million polygons per second
-     through the TA / PVR. with that in mind, a very poor estimate can be made
-     for how long the TA would take to render a frame based on the number of
-     polys pushed: 1,000,000,000 / 3,000,000 = 333 nanoseconds per polygon */
-  int64_t ns = num_polys * INT64_C(333);
+  /* give each frame 10 ms to finish rendering
+     TODO figure out a heuristic involving the number of polygons rendered */
+  int64_t ns = INT64_C(10000000);
   scheduler_start_timer(ta->scheduler, &ta_render_timer, ta, ns);
 
   if (ta->trace_writer) {