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

[A Former User]

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.

[A Former User]

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.