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