Ice shedding: move from ramp to actual slew rate

and expose with another parameter

src/modules/control_allocator/ControlAllocator.cpp

@@ -652,9 +652,13 @@ ControlAllocator::get_ice_shedding_output(hrt_abstime now, bool any_upward_motor
 	const float period_sec = _param_ice_shedding_period.get();
 	const float on_sec = _param_ice_shedding_on_time.get();
 	const float max_ice_shedding_output = _param_ice_shedding_output.get();
+	const float max_ice_shedding_slewrate = _param_ice_shedding_slewrate.get();
+	_slew_limited_ice_shedding_output.setSlewRate(max_ice_shedding_slewrate);
 
-	if (period_sec <= FLT_EPSILON || on_sec <= FLT_EPSILON || max_ice_shedding_output <= FLT_EPSILON) {
-		// The user has not configured the feature to be turned on
+	if (period_sec <= FLT_EPSILON || on_sec <= FLT_EPSILON || max_ice_shedding_output <= FLT_EPSILON
+	    || max_ice_shedding_slewrate < FLT_EPSILON) {
+		// The user has not configured the feature to be turned on, or the config makes no sense
+		_slew_limited_ice_shedding_output = 0.0f;
 		return 0.0f;
 	}
 
@@ -668,42 +672,22 @@ ControlAllocator::get_ice_shedding_output(hrt_abstime now, bool any_upward_motor
 	const bool apply_shedding = has_unused_upwards_rotors && in_forward_flight && !any_upward_motor_failed;
 
 	if (!apply_shedding) {
+		_slew_limited_ice_shedding_output = 0.0f;
 		return 0.0f;
 	}
 
 	const float elapsed_in_period = fmodf((float) now / 1_s, period_sec);
 
-	float current_ice_shedding_output = 0.0f;
+	// Pure square wave output
+	const float raw_ice_shedding_output = elapsed_in_period < on_sec ? max_ice_shedding_output : 0.0f;
 
-	const float slew_sec = 1.0f; // Time to reach full shed_ice_thrust
+	// Apply slew rate limit
+	const float dt = (float)(now - _last_ice_shedding_update) / 1_s;
 
-	// TOOD ensure this works (fails predictably...) when on_sec < 2 * slew_sec
-	// TODO if period_sec > on_sec, always output thrust? still fade it in?
-	// TODO when the params are changed in flight we essentially enter the
-	// cycle in a completely random phase, bypassing the slew limit.
-	//  - find out if this is actually dangerous
-	//  - if so, put some offset that is updated on param changes to stay in the same phase
-	//  - or redo the entire implementation with a state machine rather than this pure functional version
-
-	if (elapsed_in_period < on_sec) {
-
-		// We are in the "active" window, calculate ramping
-		if (elapsed_in_period < slew_sec) {
-			// Ramp Up
-			current_ice_shedding_output = (elapsed_in_period / slew_sec) * max_ice_shedding_output;
-
-		} else if (elapsed_in_period > (on_sec - slew_sec)) {
-			// Ramp Down
-			current_ice_shedding_output = ((on_sec - elapsed_in_period) / slew_sec) * max_ice_shedding_output;
-
-		} else {
-			// Full Throttle
-			current_ice_shedding_output = max_ice_shedding_output;
-		}
-	}
-
-	return current_ice_shedding_output;
+	_slew_limited_ice_shedding_output.update(raw_ice_shedding_output, dt);
+	_last_ice_shedding_update = now;
 
+	return _slew_limited_ice_shedding_output.getState();
 }
 
 void

src/modules/control_allocator/ControlAllocator.hpp

@@ -216,6 +216,10 @@ private:
 	Params _params{};
 	bool _has_slew_rate{false};
 
+
+	SlewRate<float> _slew_limited_ice_shedding_output;
+	hrt_abstime _last_ice_shedding_update{};
+
 	DEFINE_PARAMETERS(
 		(ParamInt<px4::params::CA_AIRFRAME>) _param_ca_airframe,
 		(ParamInt<px4::params::CA_METHOD>) _param_ca_method,
@@ -223,7 +227,8 @@ private:
 		(ParamInt<px4::params::CA_R_REV>) _param_r_rev,
 		(ParamFloat<px4::params::CA_ICE_PERIOD>) _param_ice_shedding_period,
 		(ParamFloat<px4::params::CA_ICE_ON_TIME>) _param_ice_shedding_on_time,
-		(ParamFloat<px4::params::CA_ICE_OUTPUT>) _param_ice_shedding_output
+		(ParamFloat<px4::params::CA_ICE_OUTPUT>) _param_ice_shedding_output,
+		(ParamFloat<px4::params::CA_ICE_SLEW>) _param_ice_shedding_slewrate
 	)
 
 };

src/modules/control_allocator/module.yaml

@@ -652,6 +652,17 @@ parameters:
             max: 0.2
             default: 0.0
 
+        CA_ICE_SLEW:
+            description:
+                short: Slew rate maximum for the ice shedding motor output.
+            type: float
+            decimal: 2
+            increment: 0.01
+            unit: 1/s
+            min: 0.1
+            max: 1000
+            default: 0.2
+
 # Mixer
 mixer:
     actuator_types: