Add comments to examples and add GPS_MODE_SHIELD which maps to UART mode

Author: sandeepmistry

examples/GPSLocation/GPSLocation.ino

@@ -6,7 +6,7 @@
 
   Circuit:
    - MKR board
-   - MKR GPS shield attached
+   - MKR GPS attached via I2C cable
 
   This example code is in the public domain.
 */
@@ -20,6 +20,8 @@ void setup() {
     ; // wait for serial port to connect. Needed for native USB port only
   }
 
+  // If you are using the MKR GPS as shield, change the next line to pass
+  // the GPS_MODE_SHIELD parameter to the GPS.begin(...)
   if (!GPS.begin()) {
     Serial.println("Failed to initialize GPS!");
     while (1);

examples/GPSLocationStandy/GPSLocationStandy.ino

@@ -8,7 +8,7 @@
 
   Circuit:
    - MKR board
-   - MKR GPS shield attached
+   - MKR GPS attached via I2C cable
 
   This example code is in the public domain.
 */
@@ -22,6 +22,8 @@ void setup() {
     ; // wait for serial port to connect. Needed for native USB port only
   }
 
+  // If you are using the MKR GPS as shield, change the next line to pass
+  // the GPS_MODE_SHIELD parameter to the GPS.begin(...)
   if (!GPS.begin()) {
     Serial.println("Failed to initialize GPS!");
     while (1);

keywords.txt

@@ -34,3 +34,4 @@ wakeup	KEYWORD2
 
 GPS_MODE_UART	LITERAL1
 GPS_MODE_I2C	LITERAL1
+GPS_MODE_SHIELD	LITERAL1

src/GPS.h

@@ -28,6 +28,7 @@ enum
 {
   GPS_MODE_UART,
   GPS_MODE_I2C,
+  GPS_MODE_SHIELD = GPS_MODE_UART
 };
 
 class GPSClass {