Using bela as an AVB interface?

PaulELong

I'd like to use digital ethernet over cat5 to distribute a signal using AVB and create a receiver that breaks out channels as XLR channels. Would Bela make sense for this kind of project as a receiver? Anybody do anything similar?

giuliomoro

there's this project from a few years back that allegedly had AVB working on the BBB https://github.com/induarun9086/avbtest/wiki

We never tested it, but in principle if you follow the instructions there and it does work you should end up with a virtual ALSA interface, then you could use something like this(which currently only supports audio channels) to connect the non-realtime I/O from the network to Bela's audio, analog, digital I/Os.

Both projects linked above are unsupported afaik

Clemens

Hello Giulio, Hello PaulELong!

Anybody knows if Pocketbeagle 2 still supports the precision time protocol (PTP) in its network controller?
This documentation seems to support the idea. This is required for AVB protocol to run.

What are my options to adjust for clock drift on Bela? In my limited understanding of AVB this would be needed to synchronize the audio clocks of the sender and the receiver, based on the precision time procol time stamp information. This process is called media clock recovery and I'm not sure this is actually implemented in the avbtest repository linked above.

Lastly, suppose I would want Bela Gem to be a (close-to-) AVB compatible receiver and I would want to eliminate the ALSA intermediate layer as it is implemented in the link you shared in your post - how would I go about it? Do you think that everything needs to be reimplemented or would I "only" need to replace the ALSA AVB soundcard driver?

Thank you!

giuliomoro

The AM62xx probably does support peripheral-level timestamping, which is what you need for AVB. However, there's no ethernet port on the PB2, so you can't really access the ethernet peripheral in the first place. If you are planning on using a USB-ethernet adapter, then you should check whether that does support timestamping. The real-time implications of all of this are of course pretty important: going through the USB stack bypassing the Linux kernel (e.g.: with Xenomai) is quite a task ...

OTOH, I like to think that if you have linux-level timestamping you can still get AVB to work, just with more jitter.

What are my options to adjust for clock drift on Bela?

You can in principle tweak the TLV320AIC310x's PLL via PID, but that may yield nasty sounding results (the PLL is not really meant to be adjusted while the audio is running). Software resampling may be the best option in practice.