On Wed, Sep 25, 2019 at 05:15:22PM +0100, cho...@jtan.com wrote: > I have a similar problem to Alexander Hof with a presonus audio usb > device, where attaching it reports 'only one AC iface allowed' and the > device remains (apparently totally) inaccessible. > > dmes and lsusb included below. >
According to dmesg, this is 6.5, which doesn't contain the fix for this problem. Could you try the device on a -current system? > The device and the box it plugs into are both available for prodding and > poking if it might help as neither is in use (but note I am not on tech@). > > It would appear that this assumption doesn't fully hold on some, > professional?, usb audio hardware: > > /* > * Find common clock unit. We assume all terminals > * belong to the same clock domain (ie are connected > * to the same source) > */ > > A cheap USB sound card I have to hand does not include the programmable > clock in its lsusb output, or indeed anything marked CLOCK_SOURCE. > Programmable clocks are OK, the comment states that we don't support multiple clock sources simultaneously. When audio starts, all parts of the device must be clocked by the same clock source. Pro audio interfaces use necessarily a single clock because otherwise they wouldn't be unstable in DAWs and/or for real-time effects. FWIW, I've never seen -- or even heard of -- devices using multiple clock sources simultaneously.
