Added SERIAL metadata into variant files.

Author: cmaglie

variants/arduino_due_x/variant.h

@@ -222,5 +222,30 @@ extern USARTClass Serial3;
 
 #endif
 
+// These serial port names are intended to allow libraries and architecture-neutral
+// sketches to automatically default to the correct port name for a particular type
+// of use.  For example, a GPS module would normally connect to SERIAL_PORT_HARDWARE_OPEN,
+// the first hardware serial port whose RX/TX pins are not dedicated to another use.
+//
+// SERIAL_PORT_MONITOR        Port which normally prints to the Arduino Serial Monitor
+//
+// SERIAL_PORT_USBVIRTUAL     Port which is USB virtual serial
+//
+// SERIAL_PORT_LINUXBRIDGE    Port which connects to a Linux system via Bridge library
+//
+// SERIAL_PORT_HARDWARE       Hardware serial port, physical RX & TX pins.
+//
+// SERIAL_PORT_HARDWARE_OPEN  Hardware serial ports which are open for use.  Their RX & TX
+//                            pins are NOT connected to anything by default.
+#define SERIAL_PORT_MONITOR         Serial
+#define SERIAL_PORT_USBVIRTUAL      SerialUSB
+#define SERIAL_PORT_HARDWARE_OPEN   Serial1
+#define SERIAL_PORT_HARDWARE_OPEN1  Serial2
+#define SERIAL_PORT_HARDWARE_OPEN2  Serial3
+#define SERIAL_PORT_HARDWARE        Serial
+#define SERIAL_PORT_HARDWARE1       Serial1
+#define SERIAL_PORT_HARDWARE2       Serial2
+#define SERIAL_PORT_HARDWARE3       Serial3
+
 #endif /* _VARIANT_ARDUINO_DUE_X_ */