[Jackaudio] MOTU UltraLite AVB modulo-8 channel hopping

Holger Marzen holger at marzen.de
Sun Jul 26 13:35:44 CEST 2020

Hi all,

the MOTU Ultralite AVB is a great USB audio interface that has a lot of
connections, in/outs and a buitlin mixer plus effects that can be
controlled by a web browser. Great for Linux users.

With old firmwares up to 1.3.4+558 the interface runs halfway ok on
older Linux kernels. More recent firmware uses an USB endpoint with
implicit feedback. That can be handled with linux-5.8-rc6.

With the attached kernel patch the MOTU Ultralite AVB (older model
without ESS chips) runs halfway ok with this kernel.

But from time to time the output hops modulo 8 when used with jackd:

system:playback_1 -> ends up at 9 in the interface
system:playback_2 -> ends up at 10 in the interface

I can force such a hop by changing the buffer size on the fly with
jack_bufsize. I think that every little hickup on USB confuses jackd.

My workaround is connecting system:playback_1,9,17 and 2,10,18

Stopping/starting jackd (1.9.12) resets everything.

So I am asking myself: Can this problem be fixed in jackd or is it a
problem in ALSA?

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