Copter: log event when primary GPS changes

ArduCopter/Copter.h

@@ -331,6 +331,7 @@ private:
     struct {
         uint8_t baro        : 1;    // true if baro is healthy
         uint8_t compass     : 1;    // true if compass is healthy
+        uint8_t primary_gps;        // primary gps index
     } sensor_health;
 
     // Motor Output

ArduCopter/Log.cpp

@@ -621,6 +621,12 @@ void Copter::Log_Sensor_Health()
         sensor_health.compass = compass.healthy();
         Log_Write_Error(ERROR_SUBSYSTEM_COMPASS, (sensor_health.compass ? ERROR_CODE_ERROR_RESOLVED : ERROR_CODE_UNHEALTHY));
     }
+
+    // check primary GPS
+    if (sensor_health.primary_gps != gps.primary_sensor()) {
+        sensor_health.primary_gps = gps.primary_sensor();
+        Log_Write_Event(DATA_GPS_PRIMARY_CHANGED);
+    }
 }
 
 struct PACKED log_Heli {

ArduCopter/defines.h

@@ -393,6 +393,7 @@ enum DevOptions {
 #define DATA_AVOIDANCE_ADSB_DISABLE         64
 #define DATA_AVOIDANCE_PROXIMITY_ENABLE     65
 #define DATA_AVOIDANCE_PROXIMITY_DISABLE    66
+#define DATA_GPS_PRIMARY_CHANGED            67
 
 // Centi-degrees to radians
 #define DEGX100 5729.57795f