[LAU] MOTU AVB discussion from LAC

Paul Davis paul at linuxaudiosystems.com
Sat Mar 30 04:52:04 CET 2019

On Fri, Mar 29, 2019 at 4:57 PM Max <abonnements at revolwear.com> wrote:

> Fernando Lopez-Lezcano discussed the pitfalls of using the MOTU AVB
> external audio interfaces with Linux in his paper [1] and also in the
> keynote at LAC-19.
> Let's start another thread around this card.
> Fernando mentioned that different firmwares expose different issues, but
> downgrading is possible. Issues are:
> 1. Channels are not persistent and swap around.
> 2. Total number of channels has been reduced in newer firmwares.
> 3. An endless card aquisition loop between Jack and Pulseaudio caused by
> the long time the card needs to switch sampling rate.
> 4. Seemingly erratic behavior, opening the device fails, fails again,
> again, then works suddenly.

issue 4 is not resolvable via firmware changes. it seems part of the device

> I have a couple of questions and experiences.
> Is there a table of the firmware versions somewhere (linuxaudio wiki?)
> which tell me which versions has which features (removed)?

fernando mentioned a post on "linux musicians" which describes each one.

> Are all the Class Compliant models having the same quirks as listed
> above? For example the
> MOTU UltraLite AVB versus the MOTU 624 AVB?
> Is it possible to use the Thunderbolt port to connect the card to a
> Linux computer?
> Why can't I tell ALSA to use only the first 2, 4 whatever channels of
> the device? I can only open the device if all channels are connected. Is
> this always like that or is that a limitation of MOTU's implementation?

ALSA doesn't work that way. You open a device. You tell it how many
channels you want to use.

> On my laptop with only one USB bus, If I connected the  MOTU 624 AVB and
> then another high speed usb device, the computer could not connect the
> later, because the MOTU reserved all the bandwith for itself. Connecting
> the other device and then the MOTU worked.

this is correct, and likely a sensible design choice. others may disagree.
i actually threw away a webcam because i mistakenly believed that it was no
longer working (because of this issue).
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