Is it possible to use uORB directly in a voxl module?

Dan

Hi ModalAI devs,

I'm wondering if it's possible to subscribe to a uORB topic in a voxl module. I want to subscribe to the barometer sensor and there isn't an MPA server for this.

The reason I ask is that when using the voxl-cross docker container I'm unsure which dependency is required to install to get access to the uORB headers etc.

Thanks,
Dan

Hi Dan,

You can directly subscribe to the mavlink output using the mavlink_to_px4 pipe and check for messages of type MAVLINK_MSG_ID_ALTITUDE to receive barometer updates in an MPA server.

See here for a code example.

Dan

@Matt-Turi

Hi Matt,

Thanks for the quick reply and thanks for the example that's super useful.

Just to clarify what you're saying. From my understanding when I do uorb top the topic name sensor_baro is available and I can call px4-listener sensor_baro to get an update from what I believe to be a uorb message? Are you saying that there are mavlink messages also published that will give me the same information and I can use something similar to your example to then create a barometer MPA server?

Eric Katzfey

@Dan There is no uorb to pipe bridge so not really possible. But you can run the system command px4-listener and parse the output of it. Or if what you really need is something in a Mavlink message then you can go the route Matt suggested.

There is a mavlink message you can parse for barometer data, that is the code example I sent above. In that file as well, there is an example of calling px4-listener programmatically and parsing its output - see here

Dan

@Eric-Katzfey

No problem. I was wondering if I could do that bridging myself by subscribing to the uORB topic sensor_baro and then publishing onto a barometer MPA server but wasn't sure if it was possibly to subscribe to uORB topics in the voxl SDK.

@Matt-Turi

Thanks for the clarification. I'll take a look at the px4-listener parsing too.

Dan

@Matt-Turi

Apologies. Final question for now. Who is the producer of the mavlink message for the barometer data?

Chad Sweet

The PX4 flight control software

Dan

@Chad-Sweet

Thanks Chad.