interrupt based write with ring buffer

Author: sandeepmistry

libraries/I2S/examples/tone_generator/tone_generator.ino

@@ -108,6 +108,8 @@ void playWave(int16_t* buffer, uint16_t length, float frequency, float seconds)
     // Duplicate the sample so it's sent to both the left and right channel.
     // It appears the order is right channel, left channel if you want to write
     // stereo sound.
+    while(I2S.availableForWrite() < 2);
+    
     I2S.write(sample);
     I2S.write(sample);
   }

libraries/I2S/src/I2S.cpp

@@ -8,8 +8,12 @@ I2SClass::I2SClass(SERCOM *p_sercom, uint8_t uc_index, uint8_t uc_pinSD, uint8_t
 	_uc_index(uc_index),
 	_uc_sd(uc_pinSD),
 	_uc_sck(uc_pinSCK),
-	_uc_fs(uc_pinFS)
+	_uc_fs(uc_pinFS),
+
+	_i_head(0),
+	_i_tail(0)
 {
+	memset(_aui_buffer, 0, sizeof(_aui_buffer));
 }
 
 int I2SClass::begin(int mode, long sampleRate, int bitsPerSample, int driveClock)
@@ -31,6 +35,7 @@ int I2SClass::begin(int mode, long sampleRate, int bitsPerSample, int driveClock
 		case 16:
 		case 24:
 		case 32:
+			_i_bits_per_sample = bitsPerSample;
 			break;
 
 		default:
@@ -158,6 +163,15 @@ int I2SClass::begin(int mode, long sampleRate, int bitsPerSample, int driveClock
 		_i2s->CTRLA.bit.SEREN1 = 1;
 	}
 
+	NVIC_EnableIRQ(I2S_IRQn);
+	NVIC_SetPriority(I2S_IRQn, (1 << __NVIC_PRIO_BITS) - 1);  /* set Priority */
+
+	if (_uc_index == 0) {
+		_i2s->INTENSET.bit.TXRDY0 = 1;
+	} else {
+		_i2s->INTENSET.bit.TXRDY1 = 1;
+	}
+
 	return 0;
 }
 
@@ -187,17 +201,38 @@ void I2SClass::flush()
 
 size_t I2SClass::write(uint8_t data)
 {
-	return write((int)data);
+	return write((int32_t)data);
 }
 
 size_t I2SClass::write(const uint8_t *buffer, size_t size)
 {
-	return 0;
+	size_t written = 0;
+	int bytesPerSample = (_i_bits_per_sample) / 8;
+
+	size = (size / bytesPerSample) * bytesPerSample;
+
+	while (size) {
+		int32_t data;
+
+		memcpy(&data, buffer + written, bytesPerSample);
+		written += bytesPerSample;
+		size -= bytesPerSample;
+
+		if (write(data) == 0) {
+			break;
+		}
+	}
+
+	return written;
 }
 
 size_t I2SClass::availableForWrite()
 {
-	return 0;
+	if (_i_head >= _i_tail) {
+		return I2S_BUFFER_SIZE - 1 - _i_head + _i_tail;
+	} else {
+		return _i_tail - _i_head - 1;
+	}
 }
 
 int I2SClass::read(int8_t data[], int size)
@@ -207,28 +242,51 @@ int I2SClass::read(int8_t data[], int size)
 
 int I2SClass::write(short data)
 {
-	return write((int)data);
+	return write((int32_t)data);
 }
 
 int I2SClass::write(int data)
 {
-	if (_uc_index == 0) {
-		while (!_i2s->INTFLAG.bit.TXRDY0);
-		while (_i2s->SYNCBUSY.bit.DATA0);
-	} else {
-		while (!_i2s->INTFLAG.bit.TXRDY1);
-		while (_i2s->SYNCBUSY.bit.DATA1);
+	return write((int32_t)data);
+}
+
+int I2SClass::write(int32_t data)
+{
+	int i = ((uint32_t)(_i_head + 1) % I2S_BUFFER_SIZE);
+
+	if (i == _i_tail) {
+		return 0;
 	}
 
-	_i2s->DATA[_uc_index].bit.DATA = data;
+	_aui_buffer[i] = data;
+	_i_head = i;
+
+	return 1;
+}
+
+void I2SClass::onService() {
 
 	if (_uc_index == 0) {
-		_i2s->INTFLAG.bit.TXRDY0 = 1;
-	} else {
-		_i2s->INTFLAG.bit.TXRDY1 = 1;
+		if (_i2s->INTFLAG.bit.TXRDY0) {
+			int32_t data = 0;
+
+			if (_i_head != _i_tail) {
+				data = _aui_buffer[_i_tail];
+				_i_tail = ((uint32_t)(_i_tail + 1) % I2S_BUFFER_SIZE);
+			}
+
+			while (_i2s->SYNCBUSY.bit.DATA0);
+			_i2s->DATA[_uc_index].bit.DATA = data;
+
+			_i2s->INTFLAG.bit.TXRDY0 = 1;
+		}
 	}
+}
 
-	return 1;
+extern "C" {
+	void I2S_Handler() {
+		I2S.onService();
+	}
 }
 
 /*

libraries/I2S/src/I2S.h

@@ -10,6 +10,8 @@ typedef enum {
   I2S_DSP_MODE
 } i2s_mode_t;
 
+#define I2S_BUFFER_SIZE 256
+
 class I2SClass : public Stream
 {
 public:
@@ -29,9 +31,9 @@ class I2SClass : public Stream
 
   virtual size_t availableForWrite();
 
-
   int write(short);
   int write(int);
+  int write(int32_t);
 
   int read(int8_t data[], int size);
   int read(int16_t data[], int size);
@@ -44,6 +46,8 @@ class I2SClass : public Stream
   void onReceive(void(*)(int));
   void onTransmit(void(*)(void));
 
+  void onService(void);
+
 private:
   volatile I2s *_i2s = I2S;
 
@@ -52,6 +56,12 @@ class I2SClass : public Stream
   uint8_t _uc_sd;
   uint8_t _uc_sck;
   uint8_t _uc_fs;
+
+  int _i_bits_per_sample;
+
+  int32_t _aui_buffer[I2S_BUFFER_SIZE];
+  volatile int _i_head;
+  volatile int _i_tail;
 };
 
 #undef I2S