AP_GPS_UBLOX: ask for nav settings every 20 seconds

this ensures we don't run with the wrong nav settings on a uBlox if
we get a bad checksum on the initial nav settings message

libraries/AP_GPS/AP_GPS_UBLOX.cpp

@@ -39,6 +39,8 @@ AP_GPS_UBLOX::init(enum GPS_Engine_Setting nav_setting)
     // XXX it might make sense to send some CFG_MSG,CFG_NMEA messages to get the
     // right reporting configuration.
 
+	Debug("uBlox nav_setting=%u\n", nav_setting);
+
     _port->flush();
 
     _epoch = TIME_OF_WEEK;
@@ -180,6 +182,7 @@ AP_GPS_UBLOX::_parse_gps(void)
     }
 
     if (_class == CLASS_CFG && _msg_id == MSG_CFG_NAV_SETTINGS) {
+		Debug("Got engine settings %u\n", (unsigned)_buffer.nav_settings.dynModel);
         if (_nav_setting != GPS_ENGINE_NONE &&
             _buffer.nav_settings.dynModel != _nav_setting) {
             // we've received the current nav settings, change the engine
@@ -261,6 +264,12 @@ AP_GPS_UBLOX::_parse_gps(void)
     // this ensures we don't use stale data
     if (_new_position && _new_speed) {
         _new_speed = _new_position = false;
+		_fix_count++;
+		if (_fix_count == 100) {
+			// ask for nav settings every 20 seconds
+			Debug("Asking for engine setting\n");
+			_send_message(CLASS_CFG, MSG_CFG_NAV_SETTINGS, NULL, 0);
+		}
         return true;
     }
     return false;
@@ -353,6 +362,7 @@ AP_GPS_UBLOX::_configure_gps(void)
     _configure_message_rate(CLASS_NAV, MSG_VELNED, 1);
 
     // ask for the current navigation settings
+	Debug("Asking for engine setting\n");
     _send_message(CLASS_CFG, MSG_CFG_NAV_SETTINGS, NULL, 0);
 }
 

libraries/AP_GPS/AP_GPS_UBLOX.h

@@ -164,6 +164,10 @@ private:
     uint16_t        _payload_length;
     uint16_t        _payload_counter;
 
+	// 8 bit count of fix messages processed, used for periodic
+	// processing
+    uint8_t			_fix_count;
+
     uint8_t         _class;
 
     // do we have new position information?