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The uORB is an asynchronous
subscribe() messaging API used for
inter-thread/inter-process communication. The
listener command can be used from the QGroundControl MAVLink Console to inspect topic (message) values, including the current values published by sensors.
This is a powerful debugging tool because it can be used even when QGC is connected over a wireless link (e.g. when the vehicle is flying).
listenercommand is only available on NuttX-based systems (Pixhawk, Pixracer, etc.) and Linux / OS X.
The image below demonstrates QGroundControl being used to get the value of the acceleration sensor.
For more information about how to determine what topics are available and how to call
listener see: uORB Messaging > Listing Topics and Listening in.