Support for repeated starts added to SAM Wire library

Additional interface method ported to avr for compatibility
Fix issue #2428.

Author: mattwlowe

libraries/Wire/Wire.cpp

@@ -80,8 +80,26 @@ void TwoWire::setClock(uint32_t frequency)
   TWBR = ((F_CPU / frequency) - 16) / 2;
 }
 
-uint8_t TwoWire::requestFrom(uint8_t address, uint8_t quantity, uint8_t sendStop)
+uint8_t TwoWire::requestFrom(uint8_t address, uint8_t quantity, uint32_t iaddress, uint8_t isize, uint8_t sendStop)
 {
+  if (isize > 0) {
+  // send internal address; this mode allows sending a repeated start to access
+  // some devices' internal registers. This function is executed by the hardware
+  // TWI module on other processors (for example Due's TWI_IADR and TWI_MMR registers)
+
+  beginTransmission(address);
+
+  // the maximum size of internal address is 3 bytes
+  if (isize > 3){
+    isize = 3;
+  }
+
+  // write internal register address - most significant byte first
+  while (isize-- > 0)
+    write((uint8_t)(iaddress >> (isize*8)));
+  endTransmission(false);
+  }
+
   // clamp to buffer length
   if(quantity > BUFFER_LENGTH){
     quantity = BUFFER_LENGTH;
@@ -95,6 +113,10 @@ uint8_t TwoWire::requestFrom(uint8_t address, uint8_t quantity, uint8_t sendStop
   return read;
 }
 
+uint8_t TwoWire::requestFrom(uint8_t address, uint8_t quantity, uint8_t sendStop) {
+	return requestFrom((uint8_t)address, (uint8_t)quantity, (uint32_t)0, (uint8_t)0, (uint8_t)sendStop);
+}
+
 uint8_t TwoWire::requestFrom(uint8_t address, uint8_t quantity)
 {
   return requestFrom((uint8_t)address, (uint8_t)quantity, (uint8_t)true);

libraries/Wire/Wire.h

@@ -56,6 +56,7 @@ class TwoWire : public Stream
     uint8_t endTransmission(uint8_t);
     uint8_t requestFrom(uint8_t, uint8_t);
     uint8_t requestFrom(uint8_t, uint8_t, uint8_t);
+	uint8_t requestFrom(uint8_t, uint8_t, uint32_t, uint8_t, uint8_t);
     uint8_t requestFrom(int, int);
     uint8_t requestFrom(int, int, int);
     virtual size_t write(uint8_t);