Add support for I2S MCLK. (#594)

Author: DatanoiseTV

src/AudioOutputI2S.cpp

@@ -49,6 +49,7 @@ AudioOutputI2S::AudioOutputI2S(int port, int output_mode, int dma_buf_count, int
   bclkPin = 26;
   wclkPin = 25;
   doutPin = 22;
+  mclkPin = 0;
   SetGain(1.0);
 }
 
@@ -61,6 +62,8 @@ AudioOutputI2S::AudioOutputI2S(long sampleRate, pin_size_t sck, pin_size_t data)
     hertz = sampleRate;
     bclkPin = sck;
     doutPin = data;
+    mclkPin = 0;
+    use_mclk = false;
     SetGain(1.0);
 }
 #endif
@@ -78,7 +81,7 @@ bool AudioOutputI2S::SetPinout()
 
     i2s_pin_config_t pins = {
 #if ESP_IDF_VERSION >= ESP_IDF_VERSION_VAL(4, 4, 0)
-        .mck_io_num = 0, // Unused
+        .mck_io_num = mclkPin,
 #endif
         .bck_io_num = bclkPin,
         .ws_io_num = wclkPin,
@@ -90,6 +93,8 @@ bool AudioOutputI2S::SetPinout()
     (void)bclkPin;
     (void)wclkPin;
     (void)doutPin;
+    (void)mclkPin;
+    (void)use_mclk;
     return false;
   #endif
 }
@@ -104,6 +109,22 @@ bool AudioOutputI2S::SetPinout(int bclk, int wclk, int dout)
 
   return true;
 }
+
+bool AudioOutputI2S::SetPinout(int bclk, int wclk, int dout, int mclk)
+{
+  bclkPin = bclk;
+  wclkPin = wclk;
+  doutPin = dout;
+  #ifdef ESP32
+    mclkPin = mclk;
+    if (i2sOn)
+      return SetPinout();
+  #else
+    (void)mclk;
+  #endif
+  return true;
+}
+
 bool AudioOutputI2S::SetRate(int hz)
 {
   // TODO - have a list of allowable rates from constructor, check them
@@ -147,6 +168,17 @@ bool AudioOutputI2S::SetLsbJustified(bool lsbJustified)
   return true;
 }
 
+bool AudioOutputI2S::SetMclk(bool enabled){
+  (void)enabled;
+  #ifdef ESP32
+    if (output_mode == INTERNAL_DAC || output_mode == INTERNAL_PDM)
+      return false; // Not allowed
+
+    use_mclk = enabled;
+  #endif
+  return true;
+}
+
 bool AudioOutputI2S::begin(bool txDAC)
 {
   #ifdef ESP32
@@ -219,9 +251,9 @@ bool AudioOutputI2S::begin(bool txDAC)
           .dma_buf_len = 128,
           .use_apll = use_apll, // Use audio PLL
           .tx_desc_auto_clear = true, // Silence on underflow
-          .fixed_mclk = 0, // Unused
+          .fixed_mclk = use_mclk, // Unused
 #if ESP_IDF_VERSION >= ESP_IDF_VERSION_VAL(4, 4, 0)
-          .mclk_multiple = I2S_MCLK_MULTIPLE_DEFAULT, // Unused
+          .mclk_multiple = I2S_MCLK_MULTIPLE_256, // Unused
           .bits_per_chan = I2S_BITS_PER_CHAN_DEFAULT // Use bits per sample
 #endif
       };

src/AudioOutputI2S.h

@@ -38,6 +38,7 @@ class AudioOutputI2S : public AudioOutput
     AudioOutputI2S(long sampleRate = 44100, pin_size_t sck = 26, pin_size_t data = 28);
 #endif
     bool SetPinout(int bclkPin, int wclkPin, int doutPin);
+    bool SetPinout(int bclkPin, int wclkPin, int doutPin, int mclkPin);
     virtual ~AudioOutputI2S() override;
     virtual bool SetRate(int hz) override;
     virtual bool SetBitsPerSample(int bits) override;
@@ -50,6 +51,7 @@ class AudioOutputI2S : public AudioOutput
     bool begin(bool txDAC);
     bool SetOutputModeMono(bool mono);  // Force mono output no matter the input
     bool SetLsbJustified(bool lsbJustified);  // Allow supporting non-I2S chips, e.g. PT8211 
+    bool SetMclk(bool enabled);  // Enable MCLK output (if supported)
 
   protected:
     bool SetPinout();
@@ -61,13 +63,15 @@ class AudioOutputI2S : public AudioOutput
     bool i2sOn;
     int dma_buf_count;
     int use_apll;
+    bool use_mclk;
     // We can restore the old values and free up these pins when in NoDAC mode
     uint32_t orig_bck;
     uint32_t orig_ws;
 
     uint8_t bclkPin;
     uint8_t wclkPin;
     uint8_t doutPin;
+    uint8_t mclkPin;
 
 #if defined(ARDUINO_ARCH_RP2040)
     I2S i2s;