Buffering of audio

AudioThread.cpp

@@ -26,6 +26,12 @@ double phase = 0.0;
 unsigned long lastNoteChangeTime = 0;
 // ---
 
+// Ring Buffer
+int16_t audioBuffer[AUDIO_BUFFER_SIZE];
+int audioHead = 0;
+int audioTail = 0;
+bool audioBuffering = true;
+
 void setupAudio() {
   // Configure I2S pins
   i2s.setBCLK(I2S_BCLK_PIN);
@@ -43,7 +49,9 @@ void setupAudio() {
   
   // Initialize the portable synth engine
   globalSynth = new SynthEngine(SAMPLE_RATE);
+  if (globalSynth) {
     globalSynth->loadPreset(2);
+  }
 }
 
 void loopAudio() {
@@ -71,38 +79,43 @@ void loopAudio() {
     }
   }
 
-  const int BATCH_SIZE = 16;
-
-  // Ensure we don't generate samples faster than the I2S can consume them.
-  // We write 2 samples (Left + Right) for every 1 synth sample.
-  if (i2s.availableForWrite() < BATCH_SIZE * 2) {
-      return;
+  // Produce samples in a cyclic buffer
+  int nextHead = (audioHead + 1) % AUDIO_BUFFER_SIZE;
+  if (nextHead != audioTail) {
+      if (audioHead == audioTail) {
+          audioBuffering = true;
       }
-
-  // Process a small batch of samples
-  static int16_t samples[BATCH_SIZE];
-
-  // Generate sound samples
+      int16_t sample = 0;
       if (globalSynth) {
-    // using synth engine
-    globalSynth->process(samples, BATCH_SIZE);
+          globalSynth->process(&sample, 1);
       } else {
-    // using fallback sawtooth
-    for (int i = 0; i < BATCH_SIZE; ++i) {
           if (currentFrequency > 0) {
-            //samples[i] = (int16_t)(sin(phase) * AMPLITUDE);
               phase += 2.0 * M_PI * currentFrequency / SAMPLE_RATE;
               if (phase >= 2.0 * M_PI) phase -= 2.0 * M_PI;
-            samples[i] = phase * 0.1f * AMPLITUDE;
+              sample = phase * 0.1f * AMPLITUDE;
           } else {
-            samples[i] = 0;
+              sample = 0;
           }
       }
+      audioBuffer[audioHead] = sample;
+      audioHead = nextHead;
+  } else {
+    audioBuffering = false;
   }
 
-  // write out stereo samples
-  for (int i = 0; i < BATCH_SIZE; ++i) {
-      i2s.write(samples[i]);
-      i2s.write(samples[i]);
+  // Consume samples from this buffer whenever there is capacity in i2s
+  while (!audioBuffering && audioHead != audioTail) {
+      if (i2s.availableForWrite() < 2) {
+          break;
       }
+      int16_t s = audioBuffer[audioTail];
+      i2s.write(s);
+      i2s.write(s);
+      audioTail = (audioTail + 1) % AUDIO_BUFFER_SIZE;
+  }
+
+  // Update usage stats
+  int usage = audioHead - audioTail;
+  if (usage < 0) usage += AUDIO_BUFFER_SIZE;
+  audioBufferUsage = usage;
 }

SharedState.cpp

@@ -2,6 +2,8 @@
 #include "SharedState.h"
 #include "synth_engine.h"
 
+volatile int audioBufferUsage = 0;
+
 volatile unsigned long lastLoop0Time = 0;
 volatile unsigned long lastLoop1Time = 0;
 volatile bool watchdogActive = false;

SharedState.h

@@ -3,6 +3,9 @@
 
 #include <Arduino.h>
 
+#define AUDIO_BUFFER_SIZE 512
+extern volatile int audioBufferUsage;
+
 extern volatile unsigned long lastLoop0Time;
 extern volatile unsigned long lastLoop1Time;
 extern volatile bool watchdogActive;

UIThread.cpp

@@ -182,7 +182,7 @@ void handleInput() {
 void drawUI() {
     display.clearDisplay();
 
-    if (globalSynth) {
+    {
         // Copy grid state to local buffer to minimize lock time
         struct MiniCell {
             uint8_t type;
@@ -191,7 +191,7 @@ void drawUI() {
         };
         MiniCell gridCopy[SynthEngine::GRID_W][SynthEngine::GRID_H];
 
-        {
+        if (globalSynth) {
             SynthLockGuard<SynthMutex> lock(globalSynth->gridMutex);
             for(int x=0; x<SynthEngine::GRID_W; ++x) {
                 for(int y=0; y<SynthEngine::GRID_H; ++y) {
@@ -202,9 +202,9 @@ void drawUI() {
             }
         }
 
-        int cellW = 10;
+        int cellW = 8;
         int cellH = 5;
-        int marginX = (SCREEN_WIDTH - (SynthEngine::GRID_W * cellW)) / 2;
+        int marginX = 2;
         int marginY = (SCREEN_HEIGHT - (SynthEngine::GRID_H * cellH)) / 2;
 
         for(int x=0; x<SynthEngine::GRID_W; ++x) {
@@ -245,6 +245,24 @@ void drawUI() {
                 }
             }
         }
+
+        // Draw Buffer Stats
+        int barX = 110;
+        int barY = 10;
+        int barW = 8;
+        int barH = 30;
+        
+        display.drawRect(barX, barY, barW, barH, SSD1306_WHITE);
+        
+        int usage = audioBufferUsage;
+        int fillH = (usage * (barH - 2)) / AUDIO_BUFFER_SIZE;
+        if (fillH > barH - 2) fillH = barH - 2;
+        if (fillH < 0) fillH = 0;
+        
+        display.fillRect(barX + 1, barY + (barH - 1) - fillH, barW - 2, fillH, SSD1306_WHITE);
+        
+        // display.setCursor(barX - 4, barY + barH + 4);
+        // display.print(usage);
     }
 
     display.display();