ModalAI Forum

@Chad-Sweet

Thanks Chad.

@Matt-Turi

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

@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.

@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?

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

@Eric-Katzfey

Thanks again Eric. Looks like that was the part I was missing. I'll take a look.

@Eric-Katzfey

Please correct me if my understanding is wrong. I just want to catch you whilst our time zones overlap.

I've just briefly looked through the code for MuORB and uORB. It seems that MuORB registers as a communicator with the uORB Manager and provides a bunch of callbacks that eventually invoke particular functions in the manager when the respective action happens (subscribe, callback, advertise, unsubscribe). I see process_remote_topic() calling orb_advertise() which ends up calling uORB::Utils::node_mkpath(nodepath, messageName) which in the implementation is:

//-----------------------------------------------------------------------------
//-----------------------------------------------------------------------------
int uORB::Utils::node_mkpath(char *buf, const char *orbMsgName)
{
	unsigned len;

	unsigned index = 0;

	len = snprintf(buf, orb_maxpath, "/%s/%s%d", "obj", orbMsgName, index);

	if (len >= orb_maxpath) {
		return -ENAMETOOLONG;
	}

	return OK;
}

This path (notice the /obj) then goes into node_open() which should create a file descriptor using px4_open() with the name /obj/<topic_name><index>.

Can you see point me to where I'm going wrong in my understanding as we've discussed before this directory doesn't exist on VOXL2.

@Eric-Katzfey

I was actually. That's useful - Thanks!

@Eric-Katzfey

OK great. Thanks Eric. I'll take a look and come back here if I have any further questions.

@Eric-Katzfey
Re: ModalAI uORB topic file handle location

Hi Eric. Thanks for getting back to me.

Quite possibly this is a Nuttx thing. I can use the listener just fine however I'm interested to dive a bit deeper into how you ship this data comes across from the DSP and whether I can potentially access that data directly without using uORB. I know I can use uORB to subscribe and get a file descriptor but I thought I'd ask and see if there are alternatives.

Is there documentation on ModalAI uORB implementation for the DSP?

Hi ModalAI,

PX4 mentions that you can see the topic handles in /obj. This directory doesn't exist on our VOXL2. Do you have any documentation to point me to where and how ModalAI handles uORB topics differently and where this file handle location is for VOXL2.

Thanks,
Dan

Update: I've tried again and the licenses are now available. Seems like Qualcomm needed a day or so to propagate licenses.

Thanks again for your help Eric.

@Eric-Katzfey

Hi Eric, Thanks for the reply.

From what I remember yes I did. However, if you can confirm there is nothing required from ModalAI to download the SDK other than making the correct account then I'll assume it's a problem on my end.

Hi all,

I'd like to build the fork of PX4. I'm following this guide: https://gitlab.com/voxl-public/rb5-flight/rb5-flight-px4-build-docker to first build the docker image.

I've installed the Qualcomm Package Manager but when I attempt to install the Hexagon SDK it says I don't have the appropriate license. Am I missing a step? We have purchased a VOXL2 board from yourselves, did it come with a Qualcomm license?

Thanks,
Dan