PWMOut/px4io: use disarmed values as default failsafe values

to avoid surprises where upon disarm an ESC can suddenly spool up
even though it stops when disarmed and no specific failsafe value is configured.

src/drivers/pwm_out/PWMOut.cpp

@@ -600,34 +600,6 @@ void PWMOut::update_params()
 			}
 		}
 
-		// PWM_MAIN_FAILx
-		{
-			sprintf(str, "%s_FAIL%u", prefix, i + 1);
-			int32_t pwm_failsafe = -1;
-
-			if (param_get(param_find(str), &pwm_failsafe) == PX4_OK) {
-				if (pwm_failsafe >= 0) {
-					_mixing_output.failsafeValue(i) = math::constrain(pwm_failsafe, (int32_t) 0, (int32_t) PWM_HIGHEST_MAX);
-
-					if (pwm_failsafe != _mixing_output.failsafeValue(i)) {
-						int32_t pwm_fail_new = _mixing_output.failsafeValue(i);
-						param_set(param_find(str), &pwm_fail_new);
-					}
-
-				} else {
-					if (pwm_default_channel_mask & 1 << i) {
-						_mixing_output.failsafeValue(i) = PWM_MOTOR_OFF;
-
-					} else {
-						_mixing_output.failsafeValue(i) = PWM_SERVO_STOP;
-					}
-				}
-
-			} else {
-				PX4_ERR("param %s not found", str);
-			}
-		}
-
 		// PWM_MAIN_DISx
 		{
 			sprintf(str, "%s_DIS%u", prefix, i + 1);
@@ -655,6 +627,30 @@ void PWMOut::update_params()
 			}
 		}
 
+		// PWM_MAIN_FAILx
+		{
+			sprintf(str, "%s_FAIL%u", prefix, i + 1);
+			int32_t pwm_failsafe = -1;
+
+			if (param_get(param_find(str), &pwm_failsafe) == PX4_OK) {
+				if (pwm_failsafe >= 0) {
+					_mixing_output.failsafeValue(i) = math::constrain(pwm_failsafe, (int32_t) 0, (int32_t) PWM_HIGHEST_MAX);
+
+					if (pwm_failsafe != _mixing_output.failsafeValue(i)) {
+						int32_t pwm_fail_new = _mixing_output.failsafeValue(i);
+						param_set(param_find(str), &pwm_fail_new);
+					}
+
+				} else {
+					// if no channel specific failsafe value is configured, use the disarmed value
+					_mixing_output.failsafeValue(i) = _mixing_output.disarmedValue(i);
+				}
+
+			} else {
+				PX4_ERR("param %s not found", str);
+			}
+		}
+
 		// PWM_MAIN_REVx
 		{
 			sprintf(str, "%s_REV%u", prefix, i + 1);

src/drivers/px4io/px4io.cpp

@@ -788,37 +788,6 @@ void PX4IO::update_params()
 		_pwm_max_configured = true;
 	}
 
-	// PWM_MAIN_FAILx
-	if (!_pwm_fail_configured) {
-		for (unsigned i = 0; i < _max_actuators; i++) {
-			sprintf(str, "%s_FAIL%u", prefix, i + 1);
-			int32_t pwm_fail = -1;
-
-			if (param_get(param_find(str), &pwm_fail) == PX4_OK) {
-				if (pwm_fail >= 0) {
-					_mixing_output.failsafeValue(i) = math::constrain(pwm_fail, static_cast<int32_t>(0),
-									  static_cast<int32_t>(PWM_HIGHEST_MAX));
-
-					if (pwm_fail != _mixing_output.failsafeValue(i)) {
-						int32_t pwm_fail_new = _mixing_output.failsafeValue(i);
-						param_set(param_find(str), &pwm_fail_new);
-					}
-
-				} else {
-					if (pwm_default_channel_mask & 1 << i) {
-						_mixing_output.failsafeValue(i) = PWM_MOTOR_OFF;
-
-					} else {
-						_mixing_output.failsafeValue(i) = PWM_SERVO_STOP;
-					}
-				}
-			}
-		}
-
-		_pwm_fail_configured = true;
-		updateFailsafe();
-	}
-
 	// PWM_MAIN_DISx
 	if (!_pwm_dis_configured) {
 		for (unsigned i = 0; i < _max_actuators; i++) {
@@ -845,6 +814,33 @@ void PX4IO::update_params()
 		updateDisarmed();
 	}
 
+	// PWM_MAIN_FAILx
+	if (!_pwm_fail_configured) {
+		for (unsigned i = 0; i < _max_actuators; i++) {
+			sprintf(str, "%s_FAIL%u", prefix, i + 1);
+			int32_t pwm_fail = -1;
+
+			if (param_get(param_find(str), &pwm_fail) == PX4_OK) {
+				if (pwm_fail >= 0) {
+					_mixing_output.failsafeValue(i) = math::constrain(pwm_fail, static_cast<int32_t>(0),
+									  static_cast<int32_t>(PWM_HIGHEST_MAX));
+
+					if (pwm_fail != _mixing_output.failsafeValue(i)) {
+						int32_t pwm_fail_new = _mixing_output.failsafeValue(i);
+						param_set(param_find(str), &pwm_fail_new);
+					}
+
+				} else {
+					// if no channel specific failsafe value is configured, use the disarmed value
+					_mixing_output.failsafeValue(i) = _mixing_output.disarmedValue(i);
+				}
+			}
+		}
+
+		_pwm_fail_configured = true;
+		updateFailsafe();
+	}
+
 	// PWM_MAIN_REVx
 	if (!_pwm_rev_configured) {
 		uint16_t &reverse_pwm_mask = _mixing_output.reverseOutputMask();