FlightTasks: add Descend task to land without GPS

This adds a flight task to catch the case where we want to do an
emergency descent without GPS but only a baro.

Previously, this would lead to the navigator land class being called
without position estimates which then made the flight tasks fail and
react with a flight task failsafe. This however meant that landed was
never detected and a couple of confusing error messages.

This applies if NAV_RCL_ACT is set to 3 "land".

src/lib/FlightTasks/CMakeLists.txt

@@ -63,6 +63,7 @@ list(APPEND flight_tasks_all
 	AutoFollowMe
 	Offboard
 	Failsafe
+	Descend
 	Transition
 	${flight_tasks_to_add}
 )

src/lib/FlightTasks/tasks/Descend/CMakeLists.txt

@@ -0,0 +1,39 @@
+############################################################################
+#
+#   Copyright (c) 2019 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.
+#
+############################################################################
+
+px4_add_library(FlightTaskDescend
+	FlightTaskDescend.cpp
+)
+
+target_link_libraries(FlightTaskDescend PUBLIC FlightTask)
+target_include_directories(FlightTaskDescend PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})

src/lib/FlightTasks/tasks/Descend/FlightTaskDescend.cpp

@@ -0,0 +1,62 @@
+/****************************************************************************
+ *
+ *   Copyright (c) 2019 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 FlightTaskDescend.cpp
+ */
+
+#include "FlightTaskDescend.hpp"
+
+bool FlightTaskDescend::activate(vehicle_local_position_setpoint_s last_setpoint)
+{
+	bool ret = FlightTask::activate(last_setpoint);
+	_position_setpoint = {NAN, NAN, NAN};
+	_velocity_setpoint = {NAN, NAN, NAN};
+	_thrust_setpoint = matrix::Vector3f(0.0f, 0.0f, -_param_mpc_thr_hover.get() * 0.6f);
+	_yaw_setpoint = _yaw;
+	_yawspeed_setpoint = 0.0f;
+	return ret;
+}
+
+bool FlightTaskDescend::update()
+{
+	if (PX4_ISFINITE(_velocity(2))) {
+		// land with landspeed
+		_velocity_setpoint(2) = _param_mpc_land_speed.get();
+
+	} else {
+		return false;
+	}
+
+	return true;
+
+}

src/lib/FlightTasks/tasks/Descend/FlightTaskDescend.hpp

@@ -0,0 +1,58 @@
+/****************************************************************************
+ *
+ *   Copyright (c) 2019 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 FlightTaskDescend.hpp
+ *
+ */
+
+#pragma once
+
+#include "FlightTask.hpp"
+
+class FlightTaskDescend : public FlightTask
+{
+public:
+	FlightTaskDescend() = default;
+
+	virtual ~FlightTaskDescend() = default;
+	bool update() override;
+	bool activate(vehicle_local_position_setpoint_s last_setpoint) override;
+
+private:
+	DEFINE_PARAMETERS_CUSTOM_PARENT(FlightTask,
+					(ParamFloat<px4::params::MPC_LAND_SPEED>) _param_mpc_land_speed,
+					(ParamFloat<px4::params::MPC_THR_HOVER>)
+					_param_mpc_thr_hover /**< throttle value at which vehicle is at hover equilibrium */
+				       )
+};

src/modules/commander/Commander.cpp

@@ -3197,8 +3197,7 @@ Commander::update_control_mode()
 		break;
 
 	case vehicle_status_s::NAVIGATION_STATE_DESCEND:
-		/* TODO: check if this makes sense */
-		control_mode.flag_control_auto_enabled = true;
+		control_mode.flag_control_auto_enabled = false;
 		control_mode.flag_control_rates_enabled = true;
 		control_mode.flag_control_attitude_enabled = true;
 		control_mode.flag_control_climb_rate_enabled = true;

src/modules/mc_pos_control/mc_pos_control_main.cpp

@@ -845,6 +845,28 @@ MulticopterPositionControl::start_flight_task()
 			// we want to be in this mode, reset the failure count
 			_task_failure_count = 0;
 		}
+
+	} else if (_vehicle_status.nav_state == vehicle_status_s::NAVIGATION_STATE_DESCEND) {
+
+		// Emergency descend
+		should_disable_task = false;
+		FlightTaskError error = FlightTaskError::NoError;
+
+		error =  _flight_tasks.switchTask(FlightTaskIndex::Descend);
+
+		if (error != FlightTaskError::NoError) {
+			if (prev_failure_count == 0) {
+				PX4_WARN("Descend activation failed with error: %s", _flight_tasks.errorToString(error));
+			}
+
+			task_failure = true;
+			_task_failure_count++;
+
+		} else {
+			// we want to be in this mode, reset the failure count
+			_task_failure_count = 0;
+		}
+
 	}
 
 	// manual position control

src/modules/navigator/navigator_main.cpp

@@ -591,11 +591,6 @@ Navigator::run()
 			_precland.set_mode(PrecLandMode::Required);
 			break;
 
-		case vehicle_status_s::NAVIGATION_STATE_DESCEND:
-			_pos_sp_triplet_published_invalid_once = false;
-			navigation_mode_new = &_land;
-			break;
-
 		case vehicle_status_s::NAVIGATION_STATE_AUTO_RTGS:
 			_pos_sp_triplet_published_invalid_once = false;
 			navigation_mode_new = &_dataLinkLoss;
@@ -620,6 +615,7 @@ Navigator::run()
 		case vehicle_status_s::NAVIGATION_STATE_ACRO:
 		case vehicle_status_s::NAVIGATION_STATE_ALTCTL:
 		case vehicle_status_s::NAVIGATION_STATE_POSCTL:
+		case vehicle_status_s::NAVIGATION_STATE_DESCEND:
 		case vehicle_status_s::NAVIGATION_STATE_TERMINATION:
 		case vehicle_status_s::NAVIGATION_STATE_OFFBOARD:
 		case vehicle_status_s::NAVIGATION_STATE_STAB: