fill in I2S.peek()

Author: sandeepmistry

libraries/I2S/src/I2S.cpp

@@ -179,7 +179,20 @@ int I2SClass::read()
 
 int I2SClass::peek()
 {
-  return 0;
+  uint8_t enableInterrupts = ((__get_PRIMASK() & 0x1) == 0);
+  int sample = 0;
+
+  // disable interrupts,
+  __disable_irq();
+
+  _doubleBuffer.peek(&sample, _bitsPerSample / 8);
+
+  if (enableInterrupts) {
+    // re-enable the interrupts
+    __enable_irq();
+  }
+
+  return sample;
 }
 
 void I2SClass::flush()

libraries/I2S/src/utility/I2SDoubleBuffer.cpp

@@ -80,6 +80,23 @@ size_t I2SDoubleBuffer::read(void *buffer, size_t size)
   return size;
 }
 
+size_t I2SDoubleBuffer::peek(void *buffer, size_t size)
+{
+  size_t avail = available();
+
+  if (size > avail) {
+    size = avail;
+  }
+
+  if (size == 0) {
+    return 0;
+  }
+
+  memcpy(buffer, &_buffer[_index][_readOffset[_index]], size);
+
+  return size;
+}
+
 void* I2SDoubleBuffer::data()
 {
   return (void*)_buffer[_index];

libraries/I2S/src/utility/I2SDoubleBuffer.h

@@ -35,6 +35,7 @@ class I2SDoubleBuffer
   size_t availableForWrite();
   size_t write(const void *buffer, size_t size);
   size_t read(void *buffer, size_t size);
+  size_t peek(void *buffer, size_t size);
   void* data();
   size_t available();
   void swap(int length = 0);