don't update servos if mixer_mix_threadsafe() failed to run

src/modules/px4iofirmware/mixer.cpp

@@ -295,27 +295,30 @@ mixer_tick(void)
 		/* mix */
 		mixed = mixer_mix_threadsafe(&outputs[0], &r_mixer_limits);
 
-		/* the pwm limit call takes care of out of band errors */
-		pwm_limit_calc(should_arm, should_arm_nothrottle, mixed, r_setup_pwm_reverse, r_page_servo_disarmed,
-			       r_page_servo_control_min, r_page_servo_control_max, outputs, r_page_servos, &pwm_limit);
-
-		/* clamp unused outputs to zero */
-		for (unsigned i = mixed; i < PX4IO_SERVO_COUNT; i++) {
-			r_page_servos[i] = 0;
-			outputs[i] = 0.0f;
-		}
+		/* if mixer_mix_threadsafe returns zero, it did nothing */
+		if (mixed != 0) {
 
-		/* store normalized outputs */
-		for (unsigned i = 0; i < PX4IO_SERVO_COUNT; i++) {
-			r_page_actuators[i] = FLOAT_TO_REG(outputs[i]);
-		}
+			/* the pwm limit call takes care of out of band errors */
+			pwm_limit_calc(should_arm, should_arm_nothrottle, mixed, r_setup_pwm_reverse, r_page_servo_disarmed,
+				       r_page_servo_control_min, r_page_servo_control_max, outputs, r_page_servos, &pwm_limit);
 
-		if (new_fmu_data) {
-			new_fmu_data = false;
+			/* clamp unused outputs to zero */
+			for (unsigned i = mixed; i < PX4IO_SERVO_COUNT; i++) {
+				r_page_servos[i] = 0;
+				outputs[i] = 0.0f;
+			}
 
-			up_pwm_force_update();
-		}
+			/* store normalized outputs */
+			for (unsigned i = 0; i < PX4IO_SERVO_COUNT; i++) {
+				r_page_actuators[i] = FLOAT_TO_REG(outputs[i]);
+			}
+
+			if (new_fmu_data) {
+				new_fmu_data = false;
 
+				up_pwm_force_update();
+			}
+		}
 	}
 
 	/* set arming */