create empty datalinkloss class for OBC

 Currently the class does the same as the RTL class. It is now possible
 whichclass is sued in the navigator to handle datalink loss via a
 parameter

7 files changed, 539 insertions, 3 deletions

diff --git a/src/modules/navigator/datalinkloss.cpp b/src/modules/navigator/datalinkloss.cpp
new file mode 100644
index 000000000..17e85b284
--- /dev/null
+++ b/src/modules/navigator/datalinkloss.cpp
@@ -0,0 +1,317 @@
+/****************************************************************************
+ *
+ *   Copyright (c) 2013-2014 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+/**
+ * @file datalinkloss.cpp
+ * Helper class for Data Link Loss Mode acording to the OBC rules
+ *
+ * @author Thomas Gubler <thomasgubler@gmail.com>
+ */
+
+#include <string.h>
+#include <stdlib.h>
+#include <math.h>
+#include <fcntl.h>
+
+#include <mavlink/mavlink_log.h>
+#include <systemlib/err.h>
+#include <geo/geo.h>
+
+#include <uORB/uORB.h>
+#include <uORB/topics/mission.h>
+#include <uORB/topics/home_position.h>
+
+#include "navigator.h"
+#include "datalinkloss.h"
+
+#define DELAY_SIGMA	0.01f
+
+DataLinkLoss::DataLinkLoss(Navigator *navigator, const char *name) :
+	MissionBlock(navigator, name),
+	_rtl_state(RTL_STATE_NONE),
+	_param_return_alt(this, "RETURN_ALT"),
+	_param_descend_alt(this, "DESCEND_ALT"),
+	_param_land_delay(this, "LAND_DELAY")
+{
+	/* load initial params */
+	updateParams();
+	/* initial reset */
+	on_inactive();
+}
+
+DataLinkLoss::~DataLinkLoss()
+{
+}
+
+void
+DataLinkLoss::on_inactive()
+{
+	/* reset RTL state only if setpoint moved */
+	if (!_navigator->get_can_loiter_at_sp()) {
+		_rtl_state = RTL_STATE_NONE;
+	}
+}
+
+void
+DataLinkLoss::on_activation()
+{
+	/* decide where to enter the RTL procedure when we switch into it */
+	if (_rtl_state == RTL_STATE_NONE) {
+		/* for safety reasons don't go into RTL if landed */
+		if (_navigator->get_vstatus()->condition_landed) {
+			_rtl_state = RTL_STATE_LANDED;
+			mavlink_log_info(_navigator->get_mavlink_fd(), "#audio: no RTL when landed");
+
+		/* if lower than return altitude, climb up first */
+		} else if (_navigator->get_global_position()->alt < _navigator->get_home_position()->alt
+			   + _param_return_alt.get()) {
+			_rtl_state = RTL_STATE_CLIMB;
+
+		/* otherwise go straight to return */
+		} else {
+			/* set altitude setpoint to current altitude */
+			_rtl_state = RTL_STATE_RETURN;
+			_mission_item.altitude_is_relative = false;
+			_mission_item.altitude = _navigator->get_global_position()->alt;
+		}
+	}
+
+	set_rtl_item();
+}
+
+void
+DataLinkLoss::on_active()
+{
+	if (_rtl_state != RTL_STATE_LANDED && is_mission_item_reached()) {
+		advance_rtl();
+		set_rtl_item();
+	}
+}
+
+void
+DataLinkLoss::set_rtl_item()
+{
+	struct position_setpoint_triplet_s *pos_sp_triplet = _navigator->get_position_setpoint_triplet();
+
+	/* make sure we have the latest params */
+	updateParams();
+
+	set_previous_pos_setpoint();
+	_navigator->set_can_loiter_at_sp(false);
+
+	switch (_rtl_state) {
+	case RTL_STATE_CLIMB: {
+		float climb_alt = _navigator->get_home_position()->alt + _param_return_alt.get();
+
+		_mission_item.lat = _navigator->get_global_position()->lat;
+		_mission_item.lon = _navigator->get_global_position()->lon;
+		_mission_item.altitude_is_relative = false;
+		_mission_item.altitude = climb_alt;
+		_mission_item.yaw = NAN;
+		_mission_item.loiter_radius = _navigator->get_loiter_radius();
+		_mission_item.loiter_direction = 1;
+		_mission_item.nav_cmd = NAV_CMD_WAYPOINT;
+		_mission_item.acceptance_radius = _navigator->get_acceptance_radius();
+		_mission_item.time_inside = 0.0f;
+		_mission_item.pitch_min = 0.0f;
+		_mission_item.autocontinue = true;
+		_mission_item.origin = ORIGIN_ONBOARD;
+
+		mavlink_log_info(_navigator->get_mavlink_fd(), "#audio: RTL: climb to %d meters above home",
+			(int)(climb_alt - _navigator->get_home_position()->alt));
+		break;
+	}
+
+	case RTL_STATE_RETURN: {
+		_mission_item.lat = _navigator->get_home_position()->lat;
+		_mission_item.lon = _navigator->get_home_position()->lon;
+		 // don't change altitude
+
+		 if (pos_sp_triplet->previous.valid) {
+		 	/* if previous setpoint is valid then use it to calculate heading to home */
+		 	_mission_item.yaw = get_bearing_to_next_waypoint(
+		 	        pos_sp_triplet->previous.lat, pos_sp_triplet->previous.lon,
+		 	        _mission_item.lat, _mission_item.lon);
+
+		 } else {
+		 	/* else use current position */
+		 	_mission_item.yaw = get_bearing_to_next_waypoint(
+		 	        _navigator->get_global_position()->lat, _navigator->get_global_position()->lon,
+		 	        _mission_item.lat, _mission_item.lon);
+		 }
+		_mission_item.loiter_radius = _navigator->get_loiter_radius();
+		_mission_item.loiter_direction = 1;
+		_mission_item.nav_cmd = NAV_CMD_WAYPOINT;
+		_mission_item.acceptance_radius = _navigator->get_acceptance_radius();
+		_mission_item.time_inside = 0.0f;
+		_mission_item.pitch_min = 0.0f;
+		_mission_item.autocontinue = true;
+		_mission_item.origin = ORIGIN_ONBOARD;
+
+		mavlink_log_info(_navigator->get_mavlink_fd(), "#audio: RTL: return at %d meters above home",
+			(int)(_mission_item.altitude - _navigator->get_home_position()->alt));
+		break;
+	}
+
+	case RTL_STATE_DESCEND: {
+		_mission_item.lat = _navigator->get_home_position()->lat;
+		_mission_item.lon = _navigator->get_home_position()->lon;
+		_mission_item.altitude_is_relative = false;
+		_mission_item.altitude = _navigator->get_home_position()->alt + _param_descend_alt.get();
+		_mission_item.yaw = NAN;
+		_mission_item.loiter_radius = _navigator->get_loiter_radius();
+		_mission_item.loiter_direction = 1;
+		_mission_item.nav_cmd = NAV_CMD_LOITER_TIME_LIMIT;
+		_mission_item.acceptance_radius = _navigator->get_acceptance_radius();
+		_mission_item.time_inside = 0.0f;
+		_mission_item.pitch_min = 0.0f;
+		_mission_item.autocontinue = false;
+		_mission_item.origin = ORIGIN_ONBOARD;
+
+		mavlink_log_info(_navigator->get_mavlink_fd(), "#audio: RTL: descend to %d meters above home",
+			(int)(_mission_item.altitude - _navigator->get_home_position()->alt));
+		break;
+	}
+
+	case RTL_STATE_LOITER: {
+		bool autoland = _param_land_delay.get() > -DELAY_SIGMA;
+
+		_mission_item.lat = _navigator->get_home_position()->lat;
+		_mission_item.lon = _navigator->get_home_position()->lon;
+		_mission_item.altitude_is_relative = false;
+		_mission_item.altitude = _navigator->get_home_position()->alt + _param_descend_alt.get();
+		_mission_item.yaw = NAN;
+		_mission_item.loiter_radius = _navigator->get_loiter_radius();
+		_mission_item.loiter_direction = 1;
+		_mission_item.nav_cmd = autoland ? NAV_CMD_LOITER_TIME_LIMIT : NAV_CMD_LOITER_UNLIMITED;
+		_mission_item.acceptance_radius = _navigator->get_acceptance_radius();
+		_mission_item.time_inside = _param_land_delay.get() < 0.0f ? 0.0f : _param_land_delay.get();
+		_mission_item.pitch_min = 0.0f;
+		_mission_item.autocontinue = autoland;
+		_mission_item.origin = ORIGIN_ONBOARD;
+
+		_navigator->set_can_loiter_at_sp(true);
+
+		if (autoland) {
+			mavlink_log_info(_navigator->get_mavlink_fd(), "#audio: RTL: loiter %.1fs", (double)_mission_item.time_inside);
+
+		} else {
+			mavlink_log_info(_navigator->get_mavlink_fd(), "#audio: RTL: completed, loiter");
+		}
+		break;
+	}
+
+	case RTL_STATE_LAND: {
+		_mission_item.lat = _navigator->get_home_position()->lat;
+		_mission_item.lon = _navigator->get_home_position()->lon;
+		_mission_item.altitude_is_relative = false;
+		_mission_item.altitude = _navigator->get_home_position()->alt;
+		_mission_item.yaw = NAN;
+		_mission_item.loiter_radius = _navigator->get_loiter_radius();
+		_mission_item.loiter_direction = 1;
+		_mission_item.nav_cmd = NAV_CMD_LAND;
+		_mission_item.acceptance_radius = _navigator->get_acceptance_radius();
+		_mission_item.time_inside = 0.0f;
+		_mission_item.pitch_min = 0.0f;
+		_mission_item.autocontinue = true;
+		_mission_item.origin = ORIGIN_ONBOARD;
+
+		mavlink_log_info(_navigator->get_mavlink_fd(), "#audio: RTL: land at home");
+		break;
+	}
+
+	case RTL_STATE_LANDED: {
+		_mission_item.lat = _navigator->get_home_position()->lat;
+		_mission_item.lon = _navigator->get_home_position()->lon;
+		_mission_item.altitude_is_relative = false;
+		_mission_item.altitude = _navigator->get_home_position()->alt;
+		_mission_item.yaw = NAN;
+		_mission_item.loiter_radius = _navigator->get_loiter_radius();
+		_mission_item.loiter_direction = 1;
+		_mission_item.nav_cmd = NAV_CMD_IDLE;
+		_mission_item.acceptance_radius = _navigator->get_acceptance_radius();
+		_mission_item.time_inside = 0.0f;
+		_mission_item.pitch_min = 0.0f;
+		_mission_item.autocontinue = true;
+		_mission_item.origin = ORIGIN_ONBOARD;
+
+		mavlink_log_info(_navigator->get_mavlink_fd(), "#audio: RTL: completed, landed");
+		break;
+	}
+
+	default:
+		break;
+	}
+
+	reset_mission_item_reached();
+
+	/* convert mission item to current position setpoint and make it valid */
+	mission_item_to_position_setpoint(&_mission_item, &pos_sp_triplet->current);
+	pos_sp_triplet->next.valid = false;
+
+	_navigator->set_position_setpoint_triplet_updated();
+}
+
+void
+DataLinkLoss::advance_rtl()
+{
+	switch (_rtl_state) {
+	case RTL_STATE_CLIMB:
+		_rtl_state = RTL_STATE_RETURN;
+		break;
+
+	case RTL_STATE_RETURN:
+		_rtl_state = RTL_STATE_DESCEND;
+		break;
+
+	case RTL_STATE_DESCEND:
+		/* only go to land if autoland is enabled */
+		if (_param_land_delay.get() < -DELAY_SIGMA || _param_land_delay.get() > DELAY_SIGMA) {
+			_rtl_state = RTL_STATE_LOITER;
+
+		} else {
+			_rtl_state = RTL_STATE_LAND;
+		}
+		break;
+
+	case RTL_STATE_LOITER:
+		_rtl_state = RTL_STATE_LAND;
+		break;
+
+	case RTL_STATE_LAND:
+		_rtl_state = RTL_STATE_LANDED;
+		break;
+
+	default:
+		break;
+	}
+}
diff --git a/src/modules/navigator/datalinkloss.h b/src/modules/navigator/datalinkloss.h
new file mode 100644
index 000000000..242cfac8d
--- /dev/null
+++ b/src/modules/navigator/datalinkloss.h
@@ -0,0 +1,95 @@
+/***************************************************************************
+ *
+ *   Copyright (c) 2013-2014 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+/**
+ * @file datalinkloss.cpp
+ * Helper class for Data Link Loss Mode acording to the OBC rules
+ *
+ * @author Thomas Gubler <thomasgubler@gmail.com>
+ */
+
+#ifndef NAVIGATOR_DATALINKLOSS_H
+#define NAVIGATOR_DATALINKLOSS_H
+
+#include <controllib/blocks.hpp>
+#include <controllib/block/BlockParam.hpp>
+
+#include <uORB/topics/mission.h>
+#include <uORB/topics/mission.h>
+#include <uORB/topics/home_position.h>
+#include <uORB/topics/vehicle_global_position.h>
+
+#include "navigator_mode.h"
+#include "mission_block.h"
+
+class Navigator;
+
+class DataLinkLoss : public MissionBlock
+{
+public:
+	DataLinkLoss(Navigator *navigator, const char *name);
+
+	~DataLinkLoss();
+
+	virtual void on_inactive();
+
+	virtual void on_activation();
+
+	virtual void on_active();
+
+private:
+	/**
+	 * Set the RTL item
+	 */
+	void		set_rtl_item();
+
+	/**
+	 * Move to next RTL item
+	 */
+	void		advance_rtl();
+
+	enum RTLState {
+		RTL_STATE_NONE = 0,
+		RTL_STATE_CLIMB,
+		RTL_STATE_RETURN,
+		RTL_STATE_DESCEND,
+		RTL_STATE_LOITER,
+		RTL_STATE_LAND,
+		RTL_STATE_LANDED,
+	} _rtl_state;
+
+	control::BlockParamFloat _param_return_alt;
+	control::BlockParamFloat _param_descend_alt;
+	control::BlockParamFloat _param_land_delay;
+};
+
+#endif
diff --git a/src/modules/navigator/datalinkloss_params.c b/src/modules/navigator/datalinkloss_params.c
new file mode 100644
index 000000000..bfe6ce7e1
--- /dev/null
+++ b/src/modules/navigator/datalinkloss_params.c
@@ -0,0 +1,98 @@
+/****************************************************************************
+ *
+ *   Copyright (c) 2014 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * AS IS AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/**
+ * @file rtl_params.c
+ *
+ * Parameters for RTL
+ *
+ * @author Julian Oes <julian@oes.ch>
+ */
+
+#include <nuttx/config.h>
+
+#include <systemlib/param/param.h>
+
+/*
+ * RTL parameters, accessible via MAVLink
+ */
+
+/**
+ * Loiter radius after RTL (FW only)
+ *
+ * Default value of loiter radius after RTL (fixedwing only).
+ *
+ * @unit meters
+ * @min 0.0
+ * @group RTL
+ */
+PARAM_DEFINE_FLOAT(RTL_LOITER_RAD, 50.0f);
+
+/**
+ * RTL altitude
+ *
+ * Altitude to fly back in RTL in meters
+ *
+ * @unit meters
+ * @min 0
+ * @max 1
+ * @group RTL
+ */
+PARAM_DEFINE_FLOAT(RTL_RETURN_ALT, 100);
+
+
+/**
+ * RTL loiter altitude
+ *
+ * Stay at this altitude above home position after RTL descending.
+ * Land (i.e. slowly descend) from this altitude if autolanding allowed.
+ *
+ * @unit meters
+ * @min 0
+ * @max 100
+ * @group RTL
+ */
+PARAM_DEFINE_FLOAT(RTL_DESCEND_ALT, 20);
+
+/**
+ * RTL delay
+ *
+ * Delay after descend before landing in RTL mode.
+ * If set to -1 the system will not land but loiter at NAV_LAND_ALT.
+ *
+ * @unit seconds
+ * @min -1
+ * @max
+ * @group RTL
+ */
+PARAM_DEFINE_FLOAT(RTL_LAND_DELAY, -1.0f);
diff --git a/src/modules/navigator/module.mk b/src/modules/navigator/module.mk
index b50198996..a1e42ec38 100644
--- a/src/modules/navigator/module.mk
+++ b/src/modules/navigator/module.mk
@@ -49,7 +49,9 @@ SRCS		= navigator_main.cpp \
 		  offboard.cpp \
 		  mission_feasibility_checker.cpp \
 		  geofence.cpp \
-		  geofence_params.c
+		  geofence_params.c \
+		  datalinkloss.cpp \
+		  datalinkloss_params.c
 
 INCLUDE_DIRS	 += $(MAVLINK_SRC)/include/mavlink
 
diff --git a/src/modules/navigator/navigator.h b/src/modules/navigator/navigator.h
index 8edbb63b3..d0b2ed841 100644
--- a/src/modules/navigator/navigator.h
+++ b/src/modules/navigator/navigator.h
@@ -35,6 +35,7 @@
  * Helper class to access missions
  * @author Julian Oes <julian@oes.ch>
  * @author Anton Babushkin <anton.babushkin@me.com>
+ * @author Thomas Gubler <thomasgubler@gmail.com>
  */
 
 #ifndef NAVIGATOR_H
@@ -57,6 +58,7 @@
 #include "loiter.h"
 #include "rtl.h"
 #include "offboard.h"
+#include "datalinkloss.h"
 #include "geofence.h"
 
 /**
@@ -165,6 +167,7 @@ private:
 	Loiter		_loiter;			/**< class that handles loiter */
 	RTL 		_rtl;				/**< class that handles RTL */
 	Offboard	_offboard;			/**< class that handles offboard */
+	DataLinkLoss	_dataLinkLoss;			/**< class that handles offboard */
 
 	NavigatorMode *_navigation_mode_array[NAVIGATOR_MODE_ARRAY_SIZE];	/**< array of navigation modes */
 
@@ -173,6 +176,7 @@ private:
 
 	control::BlockParamFloat _param_loiter_radius;	/**< loiter radius for fixedwing */
 	control::BlockParamFloat _param_acceptance_radius;	/**< acceptance for takeoff */
+	control::BlockParamInt _param_datalinkloss_obc;	/**< if true: obc mode on data link loss enabled */
 	/**
 	 * Retrieve global position
 	 */
diff --git a/src/modules/navigator/navigator_main.cpp b/src/modules/navigator/navigator_main.cpp
index ba46bd568..1ce6770c9 100644
--- a/src/modules/navigator/navigator_main.cpp
+++ b/src/modules/navigator/navigator_main.cpp
@@ -40,6 +40,7 @@
  * @author Jean Cyr <jean.m.cyr@gmail.com>
  * @author Julian Oes <julian@oes.ch>
  * @author Anton Babushkin <anton.babushkin@me.com>
+ * @author Thomas Gubler <thomasgubler@gmail.com>
  */
 
 #include <nuttx/config.h>
@@ -125,10 +126,12 @@ Navigator::Navigator() :
 	_loiter(this, "LOI"),
 	_rtl(this, "RTL"),
 	_offboard(this, "OFF"),
+	_dataLinkLoss(this, "DLL"),
 	_can_loiter_at_sp(false),
 	_pos_sp_triplet_updated(false),
 	_param_loiter_radius(this, "LOITER_RAD"),
-	_param_acceptance_radius(this, "ACC_RAD")
+	_param_acceptance_radius(this, "ACC_RAD"),
+	_param_datalinkloss_obc(this, "DLL_OBC")
 {
 	/* Create a list of our possible navigation types */
 	_navigation_mode_array[0] = &_mission;
@@ -376,7 +379,13 @@ Navigator::task_main()
 				_navigation_mode = &_rtl;
 				break;
 			case NAVIGATION_STATE_AUTO_RTGS:
-				_navigation_mode = &_rtl; /* TODO: change this to something else */
+				/* Use complex data link loss mode only when enabled via param
+				* otherwise use rtl */
+				if (_param_datalinkloss_obc.get() != 0) {
+					_navigation_mode = &_dataLinkLoss;
+				} else {
+					_navigation_mode = &_rtl; /* TODO: change this to something else */
+				}
 				break;
 			case NAVIGATION_STATE_LAND:
 			case NAVIGATION_STATE_TERMINATION:
diff --git a/src/modules/navigator/navigator_params.c b/src/modules/navigator/navigator_params.c
index 084afe340..afaf1c3c3 100644
--- a/src/modules/navigator/navigator_params.c
+++ b/src/modules/navigator/navigator_params.c
@@ -37,6 +37,7 @@
  * Parameters for navigator in general
  *
  * @author Julian Oes <julian@oes.ch>
+ * @author Thomas Gubler <thomasgubler@gmail.com>
  */
 
 #include <nuttx/config.h>
@@ -64,3 +65,13 @@ PARAM_DEFINE_FLOAT(NAV_LOITER_RAD, 50.0f);
  * @group Mission
  */
 PARAM_DEFINE_FLOAT(NAV_ACC_RAD, 25.0f);
+
+/**
+ * Set OBC mode for data link loss
+ *
+ * If set to 1 the behaviour on data link loss is set to a mode according to the OBC rules
+ *
+ * @min 0
+ * @group Mission
+ */
+PARAM_DEFINE_INT32(NAV_DLL_OBC, 0);