Add enable and disable data register interrupt APIs for UART

Author: sandeepmistry

cores/arduino/SERCOM.cpp

@@ -173,6 +173,16 @@ int SERCOM::writeDataUART(uint8_t data)
   return 1;
 }
 
+void SERCOM::enableDataRegisterEmptyInterruptUART()
+{
+  sercom->USART.INTENSET.bit.DRE = 1;
+}
+
+void SERCOM::disableDataRegisterEmptyInterruptUART()
+{
+  sercom->USART.INTENSET.bit.DRE = 0;
+}
+
 /*	=========================
  *	===== Sercom SPI
  *	=========================

cores/arduino/SERCOM.h

@@ -163,6 +163,8 @@ class SERCOM
 		int writeDataUART(uint8_t data) ;
 		bool isUARTError() ;
 		void acknowledgeUARTError() ;
+		void enableDataRegisterEmptyInterruptUART();
+		void disableDataRegisterEmptyInterruptUART();
 
 		/* ========== SPI ========== */
 		void initSPI(SercomSpiTXPad mosi, SercomRXPad miso, SercomSpiCharSize charSize, SercomDataOrder dataOrder) ;