Rover: log GPS packets as they come in

APMrover2/APMrover2.pde

@@ -722,9 +722,6 @@ static void medium_loop()
 
 			if (g.log_bitmask & MASK_LOG_NTUN)
 				Log_Write_Nav_Tuning();
-
-			if (g.log_bitmask & MASK_LOG_GPS)
-				DataFlash.Log_Write_GPS(g_gps, current_loc.alt);
 			break;
 
 		// This case controls the slow loop
@@ -799,9 +796,17 @@ static void one_second_loop()
 
 static void update_GPS(void)
 {        
+    static uint32_t last_gps_reading;
 	g_gps->update();
 	update_GPS_light();
 
+    if (g_gps->last_message_time_ms() != last_gps_reading) {
+        last_gps_reading = g_gps->last_message_time_ms();
+        if (g.log_bitmask & MASK_LOG_GPS) {
+            DataFlash.Log_Write_GPS(g_gps, current_loc.alt);
+        }
+    }
+
     have_position = ahrs.get_position(&current_loc);
 
 	if (g_gps->new_data && g_gps->status() >= GPS::GPS_OK_FIX_3D) {