Don't try to mix if we have no mixer installed.

apps/px4/fmu/fmu.cpp

@@ -226,7 +226,7 @@ FMUServo::task_main()
 	while (!_task_should_exit) {
 
 		/* sleep waiting for data, but no more than 100ms */
-		int ret = ::poll(&fds[0], 2, 100);
+		int ret = ::poll(&fds[0], 2, 1000);
 
 		/* this would be bad... */
 		if (ret < 0) {
@@ -239,9 +239,12 @@ FMUServo::task_main()
 		if (fds[0].revents & POLLIN) {
 			float outputs[num_outputs];
 
-			/* get controls */
+			/* get controls - must always do this to avoid spinning */
 			orb_copy(ORB_ID_VEHICLE_ATTITUDE_CONTROLS, _t_actuators, &_controls);
 
+			/* can we mix? */
+			if (_mixers != nullptr) {
+
 				/* do mixing */
 				_mixers->mix(&outputs[0], num_outputs);
 
@@ -252,6 +255,7 @@ FMUServo::task_main()
 					up_pwm_servo_set(i, 1500 + (600 * outputs[i]));
 				}
 			}
+		}
 
 		/* how about an arming update? */
 		if (fds[1].revents & POLLIN) {