add I2S slave mode support

Author: sandeepmistry

libraries/I2S/src/I2S.cpp

@@ -46,6 +46,16 @@ I2SClass::I2SClass(uint8_t deviceIndex, uint8_t clockGenerator, uint8_t sdPin, u
 }
 
 int I2SClass::begin(int mode, long sampleRate, int bitsPerSample)
+{
+  return begin(mode, sampleRate, bitsPerSample, true);
+}
+
+int I2SClass::begin(int mode, int bitsPerSample)
+{
+  return begin(mode, 0, bitsPerSample, false);
+}
+
+int I2SClass::begin(int mode, long sampleRate, int bitsPerSample, bool driveClock)
 {
   if (_state != I2S_STATE_IDLE) {
     return 1;
@@ -88,7 +98,15 @@ int I2SClass::begin(int mode, long sampleRate, int bitsPerSample)
 
   _beginCount++;
 
-  enableClock(sampleRate * 2 * bitsPerSample);
+  if (driveClock) {
+    enableClock(sampleRate * 2 * bitsPerSample);
+
+    i2sd.setSerialClockSelectMasterClockDiv(_deviceIndex);
+    i2sd.setFrameSyncSelectSerialClockDiv(_deviceIndex);
+  } else {
+    i2sd.setSerialClockSelectPin(_deviceIndex);
+    i2sd.setFrameSyncSelectPin(_deviceIndex);
+  }
 
   i2sd.disable();
   i2sd.set1BitDelay(_deviceIndex);
@@ -99,7 +117,9 @@ int I2SClass::begin(int mode, long sampleRate, int bitsPerSample)
   pinPeripheral(_fsPin, PIO_COM);
 
   i2sd.setSlotAdjustedLeft(_deviceIndex);
-  i2sd.setClockUnit(_deviceIndex);
+  if (driveClock) {
+    i2sd.setClockUnit(_deviceIndex);
+  }
 
   pinPeripheral(_sdPin, PIO_COM);
 

libraries/I2S/src/I2S.h

@@ -33,6 +33,7 @@ class I2SClass : public Stream
   I2SClass(uint8_t deviceIndex, uint8_t clockGenerator, uint8_t sdPin, uint8_t sckPin, uint8_t fsPin);
 
   int begin(int mode, long sampleRate, int bitsPerSample);
+  int begin(int mode, int bitsPerSample);
   void end();
 
   // from Stream
@@ -57,6 +58,8 @@ class I2SClass : public Stream
   void onReceive(void(*)(void));
 
 private:
+  int begin(int mode, long sampleRate, int bitsPerSample, bool driveClock);
+
   void enableClock(int divider);
   void disableClock();
 

libraries/I2S/src/utility/SAMD21_I2SDevice.h

@@ -47,6 +47,22 @@ class I2SDevice_SAMD21G18x {
     return (index == 0) ? I2S_GCLK_ID_0 : I2S_GCLK_ID_1;
   }
 
+  inline void setSerialClockSelectMasterClockDiv(int index) {
+    i2s.CLKCTRL[index].bit.SCKSEL = I2S_CLKCTRL_SCKSEL_MCKDIV_Val;
+  }
+
+  inline void setSerialClockSelectPin(int index) {
+    i2s.CLKCTRL[index].bit.SCKSEL = I2S_CLKCTRL_SCKSEL_SCKPIN_Val;
+  }
+
+  inline void setFrameSyncSelectSerialClockDiv(int index) {
+    i2s.CLKCTRL[index].bit.FSSEL = I2S_CLKCTRL_FSSEL_SCKDIV_Val;
+  }
+
+  inline void setFrameSyncSelectPin(int index) {
+    i2s.CLKCTRL[index].bit.FSSEL = I2S_CLKCTRL_FSSEL_FSPIN_Val;
+  }
+
   inline void set1BitDelay(int index) {
     i2s.CLKCTRL[index].bit.BITDELAY = I2S_CLKCTRL_BITDELAY_I2S_Val;
   }