Simple mixer: add output slew rate

This adds the option to limit the rate of change (slew rate) of an output that's mixed by a simple mixer.
To enable it, a positive number has to be added at the end (6th number) of the output scaler line of the mixer,
specifying the min rise time of this output.
E.g. O:      10000  10000      0 -10000  10000 20000 for a rise time of 2s, resp. a max slew rate of 0.5s^-1.

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

src/lib/mixer_module/mixer_module.cpp

@@ -239,11 +239,11 @@ void MixingOutput::unregister()
 	}
 }
 
-void MixingOutput::updateOutputSlewrate()
+void MixingOutput::updateOutputSlewrateMultirotorMixer()
 {
 	const hrt_abstime now = hrt_absolute_time();
-	const float dt = math::constrain((now - _time_last_mix) / 1e6f, 0.0001f, 0.02f);
-	_time_last_mix = now;
+	const float dt = math::constrain((now - _time_last_dt_update_multicopter) / 1e6f, 0.0001f, 0.02f);
+	_time_last_dt_update_multicopter = now;
 
 	// maximum value the outputs of the multirotor mixer are allowed to change in this cycle
 	// factor 2 is needed because actuator outputs are in the range [-1,1]
@@ -251,6 +251,16 @@ void MixingOutput::updateOutputSlewrate()
 	_mixers->set_max_delta_out_once(delta_out_max);
 }
 
+void MixingOutput::updateOutputSlewrateSimplemixer()
+{
+	const hrt_abstime now = hrt_absolute_time();
+	const float dt = math::constrain((now - _time_last_dt_update_simple_mixer) / 1e6f, 0.0001f, 0.02f);
+	_time_last_dt_update_simple_mixer = now;
+
+	// set dt for slew rate limiter in SimpleMixer (is reset internally after usig it, so needs to be set on every update)
+	_mixers->set_dt_once(dt);
+}
+
 
 unsigned MixingOutput::motorTest()
 {
@@ -355,9 +365,11 @@ bool MixingOutput::update()
 	}
 
 	if (_param_mot_slew_max.get() > FLT_EPSILON) {
-		updateOutputSlewrate();
+		updateOutputSlewrateMultirotorMixer();
 	}
 
+	updateOutputSlewrateSimplemixer(); // update dt for output slew rate in simple mixer
+
 	unsigned n_updates = 0;
 
 	/* get controls for required topics */

src/lib/mixer_module/mixer_module.hpp

@@ -191,7 +191,8 @@ private:
 
 	unsigned motorTest();
 
-	void updateOutputSlewrate();
+	void updateOutputSlewrateMultirotorMixer();
+	void updateOutputSlewrateSimplemixer();
 	void setAndPublishActuatorOutputs(unsigned num_outputs, actuator_outputs_s &actuator_outputs);
 	void publishMixerStatus(const actuator_outputs_s &actuator_outputs);
 	void updateLatencyPerfCounter(const actuator_outputs_s &actuator_outputs);
@@ -244,7 +245,8 @@ private:
 	actuator_controls_s _controls[actuator_controls_s::NUM_ACTUATOR_CONTROL_GROUPS] {};
 	actuator_armed_s _armed{};
 
-	hrt_abstime _time_last_mix{0};
+	hrt_abstime _time_last_dt_update_multicopter{0};
+	hrt_abstime _time_last_dt_update_simple_mixer{0};
 	unsigned _max_topic_update_interval_us{0}; ///< max _control_subs topic update interval (0=unlimited)
 
 	bool _throttle_armed{false};