Hi all,

I am using the MOTU Ultralite AVB USB audio interface. With recent firmwares MOTU uses implicit feedback. Kernel 5.8-rc6 can handle it when I apply the attached patch with the MOTU signatures.

But both with the old and the new firmware there is an occasional modulo 8 output channel hopping. What goes out to system:playback_1 in jackd ends on channel 1, 9 or 17 in the interface. Same for system:playback_2.

I can force a hop when changing jackd's buffer size on the fly with jack_bufsize.

One user reports this issue with ALSA clients, too, so it's probably no jackd issue.

Since I never found this issue reported from a Windows or Mac user it may be buried deep in the ALSA kernel code.

For me it seems that flaws/timeouts in the USB communication force this hopping in the ALSA kernel.

Any ideas how to find out where the hopping happens? sound/usb/endpoint.c ? sound/usb/stream.c?

Regards Holger