Add SPI.transfer16(...) API's

cores/arduino/SERCOM.cpp

@@ -262,6 +262,11 @@ void SERCOM::setDataOrderSPI(SercomDataOrder dataOrder)
   enableSPI();
 }
 
+SercomDataOrder SERCOM::getDataOrderSPI()
+{
+  return (sercom->SPI.CTRLA.bit.DORD ? LSB_FIRST : MSB_FIRST);
+}
+
 void SERCOM::setBaudrateSPI(uint8_t divider)
 {
   //Can't divide by 0

cores/arduino/SERCOM.h

@@ -173,6 +173,7 @@ class SERCOM
 		void enableSPI( void ) ;
 		void disableSPI( void ) ;
 		void setDataOrderSPI(SercomDataOrder dataOrder) ;
+		SercomDataOrder getDataOrderSPI( void ) ;
 		void setBaudrateSPI(uint8_t divider) ;
 		void setClockModeSPI(SercomSpiClockMode clockMode) ;
 		void writeDataSPI(uint8_t data) ;

libraries/SPI/SPI.cpp

@@ -194,6 +194,22 @@ byte SPIClass::transfer(uint8_t data)
   return _p_sercom->readDataSPI() & 0xFF;
 }
 
+uint16_t SPIClass::transfer16(uint16_t data) {
+  union { uint16_t val; struct { uint8_t lsb; uint8_t msb; }; } t;
+
+  t.val = data;
+
+  if (_p_sercom->getDataOrderSPI() == LSB_FIRST) {
+    t.lsb = transfer(t.lsb);
+    t.msb = transfer(t.msb);
+  } else {
+    t.msb = transfer(t.msb);
+    t.lsb = transfer(t.lsb);
+  }
+
+  return t.val;
+}
+
 void SPIClass::attachInterrupt() {
   // Should be enableInterrupt()
 }

libraries/SPI/SPI.h

@@ -95,6 +95,7 @@ class SPIClass {
 
 
   byte transfer(uint8_t data);
+  uint16_t transfer16(uint16_t data);
   inline void transfer(void *buf, size_t count);
 
   // Transaction Functions