Commander: add max flight time RTL

Adds COM_FLT_TIME_MAX param and logic in Commander to enforce RTL when
flight time is above this value. User can only override to LAND mode,
but not proceed flight beyond that.

Signed-off-by: Silvan Fuhrer <silvan@auterion.com>

src/modules/commander/Commander.cpp

@@ -2916,6 +2916,24 @@ Commander::run()
 		/* Get current timestamp */
 		const hrt_abstime now = hrt_absolute_time();
 
+		// Trigger RTL if flight time is larger than max flight time specified in COM_FLT_TIME_MAX.
+		// The user is not able to override once above threshold, except for triggering Land.
+		if (!_vehicle_land_detected.landed
+		    && _param_com_flt_time_max.get() > FLT_EPSILON
+		    && _internal_state.main_state != commander_state_s::MAIN_STATE_AUTO_RTL
+		    && _internal_state.main_state != commander_state_s::MAIN_STATE_AUTO_LAND
+		    && (now - _status.takeoff_time) > (1_s * _param_com_flt_time_max.get())) {
+			main_state_transition(_status, commander_state_s::MAIN_STATE_AUTO_RTL, _status_flags, _internal_state);
+			_status_changed = true;
+			mavlink_log_critical(&_mavlink_log_pub, "Maximum flight time reached, abort operation and RTL");
+			/* EVENT
+			* @description
+			* Maximal flight time reached, return to launch.
+			*/
+			events::send(events::ID("commander_max_flight_time_rtl"), {events::Log::Critical, events::LogInternal::Warning},
+				     "Maximum flight time reached, abort operation and RTL");
+		}
+
 		// automatically set or update home position
 		if (_param_com_home_en.get() && !_home_pub.get().manual_home) {
 			if (!_armed.armed && _vehicle_land_detected.landed) {

src/modules/commander/Commander.hpp

@@ -273,7 +273,8 @@ private:
 		(ParamFloat<px4::params::CP_DIST>) _param_cp_dist,
 
 		(ParamFloat<px4::params::BAT_LOW_THR>) _param_bat_low_thr,
-		(ParamFloat<px4::params::BAT_CRIT_THR>) _param_bat_crit_thr
+		(ParamFloat<px4::params::BAT_CRIT_THR>) _param_bat_crit_thr,
+		(ParamInt<px4::params::COM_FLT_TIME_MAX>) _param_com_flt_time_max
 	)
 
 	enum class PrearmedMode {

src/modules/commander/commander_params.c

@@ -1065,3 +1065,21 @@ PARAM_DEFINE_INT32(COM_ARM_SDCARD, 1);
  * @unit m/s
  */
 PARAM_DEFINE_FLOAT(COM_WIND_WARN, -1.f);
+
+/**
+ * Maximum allowed flight time
+ *
+ * The vehicle aborts the current operation and returns to launch when
+ * the time since takeoff is above this value. It is not possible to resume the
+ * mission or switch to any mode other than RTL or Land.
+ *
+ * Set a nagative value to disable.
+ *
+ *
+ * @unit s
+ * @min -1
+ * @max 10000
+ * @value 0 Disable
+ * @group Commander
+ */
+PARAM_DEFINE_INT32(COM_FLT_TIME_MAX, -1);