add double buffer for I2S DMA writes

Author: sandeepmistry

libraries/I2S/src/I2S.cpp

@@ -36,12 +36,13 @@ I2SClass::I2SClass(uint8_t deviceIndex, uint8_t clockGenerator, uint8_t sdPin, u
   _fsPin(fsPin),
 
   _dmaChannel(-1),
+  _dmaTransferInProgress(false),
 
   _onTransmit(NULL)
 {
 }
 
-int I2SClass::begin(int mode, long sampleRate, int bitsPerSample, int driveClock)
+int I2SClass::begin(int mode, long sampleRate, int bitsPerSample)
 {
   switch (mode) {
     case I2S_PHILIPS_MODE:
@@ -101,10 +102,11 @@ int I2SClass::begin(int mode, long sampleRate, int bitsPerSample, int driveClock
 
   DMA.incSrc(_dmaChannel);
   DMA.onTransferComplete(_dmaChannel, I2SClass::onDmaTransferComplete);
-  DMA.onTransferError(_dmaChannel, I2SClass::onDmaTransferError);
   DMA.setTriggerSource(_dmaChannel, i2sd.dmaTriggerSource(_deviceIndex));
   DMA.setTransferWidth(_dmaChannel, bitsPerSample);
 
+  _doubleBuffer.reset();
+
   return 0;
 }
 
@@ -165,7 +167,20 @@ size_t I2SClass::write(const uint8_t *buffer, size_t size)
 
 size_t I2SClass::availableForWrite()
 {
-  return 2;
+  uint8_t enableInterrupts = ((__get_PRIMASK() & 0x1) == 0);
+  size_t space;
+
+  // disable interrupts,
+  __disable_irq();
+
+  space = _doubleBuffer.availableForWrite();
+
+  if (enableInterrupts) {
+    // re-enable the interrupts
+    __enable_irq();
+  }
+
+  return space;
 }
 
 size_t I2SClass::write(int sample)
@@ -186,7 +201,28 @@ size_t I2SClass::write(int32_t sample)
 
 size_t I2SClass::write(const void *buffer, size_t size)
 {
-  return 0;
+  uint8_t enableInterrupts = ((__get_PRIMASK() & 0x1) == 0);
+  size_t written;
+
+  // disable interrupts,
+  __disable_irq();
+
+  written = _doubleBuffer.write(buffer, size);
+
+  if (_dmaTransferInProgress == false) {
+    _dmaTransferInProgress = true;
+
+    DMA.transfer(_dmaChannel, _doubleBuffer.data(), i2sd.data(_deviceIndex), _doubleBuffer.available());
+
+    _doubleBuffer.swap();
+  }
+
+  if (enableInterrupts) {
+    // re-enable the interrupts
+    __enable_irq();
+  }
+
+  return written;
 }
 
 void I2SClass::onTransmit(void(*function)(void))
@@ -235,19 +271,19 @@ void I2SClass::onDmaTransferComplete(int channel)
   }
 }
 
-void I2SClass::onDmaTransferError(int channel)
-{
-  if (I2S._dmaChannel == channel) {
-    I2S.onTransferError();
-  }
-}
-
 void I2SClass::onTransferComplete(void)
 {
-}
+  if (_doubleBuffer.available()) {
+    DMA.transfer(_dmaChannel, _doubleBuffer.data(), i2sd.data(_deviceIndex), _doubleBuffer.available());
 
-void I2SClass::onTransferError(void)
-{
+    _doubleBuffer.swap();
+  } else {
+    _dmaTransferInProgress = false;
+  }
+
+  if (_onTransmit) {
+    _onTransmit();
+  }
 }
 
 /*

libraries/I2S/src/I2S.h

@@ -21,18 +21,19 @@
 
 #include <Arduino.h>
 
+#include "utility/I2SDoubleBuffer.h"
+
 typedef enum {
   I2S_PHILIPS_MODE
 } i2s_mode_t;
 
-#define I2S_BUFFER_SIZE 512
 
 class I2SClass : public Stream
 {
 public:
   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 driveClock = 1);
+  int begin(int mode, long sampleRate, int bitsPerSample);
   void end();
 
   // from Stream
@@ -58,10 +59,8 @@ class I2SClass : public Stream
   void disableClock();
 
   static void onDmaTransferComplete(int);
-  static void onDmaTransferError(int);
 
   void onTransferComplete(void);
-  void onTransferError(void);
 
 private:
   static int _beginCount;
@@ -74,6 +73,9 @@ class I2SClass : public Stream
 
   int _dmaChannel;
 
+  bool _dmaTransferInProgress;
+  I2SDoubleBuffer _doubleBuffer;
+
   void (*_onTransmit)(void);
 };
 

libraries/I2S/src/utility/I2SDoubleBuffer.cpp

@@ -0,0 +1,82 @@
+/*
+  Copyright (c) 2016 Arduino LLC.  All right reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+  See the GNU Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#include <string.h>
+
+#include "I2SDoubleBuffer.h"
+
+I2SDoubleBuffer::I2SDoubleBuffer()
+{
+  reset();
+}
+
+I2SDoubleBuffer::~I2SDoubleBuffer()
+{
+}
+
+void I2SDoubleBuffer::reset()
+{
+  _index = 0;
+  _length[0] = 0;
+  _length[1] = 0;
+}
+
+size_t I2SDoubleBuffer::availableForWrite()
+{
+  return (I2S_BUFFER_SIZE - _length[_index]);
+}
+
+size_t I2SDoubleBuffer::write(const void *buffer, size_t size)
+{
+  size_t space = availableForWrite();
+
+  if (size > space) {
+    size = space;
+  }
+
+  if (size == 0) {
+    return 0;
+  }
+
+  memcpy(&_buffer[_index][_length[_index]], buffer, size);
+
+  _length[_index] += size;
+
+  return size;
+}
+
+void* I2SDoubleBuffer::data()
+{
+  return (void*)_buffer[_index];
+}
+
+size_t I2SDoubleBuffer::available()
+{
+  return _length[_index];
+}
+
+void I2SDoubleBuffer::swap()
+{
+  if (_index == 0) {
+    _index = 1;
+  } else {
+    _index = 0;
+  }
+
+  _length[_index] = 0;
+}

libraries/I2S/src/utility/I2SDoubleBuffer.h

@@ -0,0 +1,47 @@
+/*
+  Copyright (c) 2016 Arduino LLC.  All right reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+  See the GNU Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#ifndef _I2S_DOUBLE_BUFFER_H_INCLUDED
+#define _I2S_DOUBLE_BUFFER_H_INCLUDED
+
+#include <stddef.h>
+#include <stdint.h>
+
+#define I2S_BUFFER_SIZE 512
+
+class I2SDoubleBuffer
+{
+public:
+  I2SDoubleBuffer();
+  virtual ~I2SDoubleBuffer();
+
+  void reset();
+
+  size_t availableForWrite();
+  size_t write(const void *buffer, size_t size);
+  void* data();
+  size_t available();
+  void swap();
+
+private:
+  uint8_t _buffer[2][I2S_BUFFER_SIZE];
+  volatile int _length[2];
+  volatile int _index; 
+};
+
+#endif

libraries/I2S/src/utility/SAMD21_I2SDevice.h

@@ -157,6 +157,10 @@ class I2SDevice_SAMD21G18x {
     }
   }
 
+  inline void* data(int index) {
+    return (void*)&i2s.DATA[index].reg;
+  }
+
 private:
   volatile I2s &i2s;
 };