Romain Michon wrote:
> I'm trying to use two audio interfaces (Guitar Link UC6102) in
> parallel in Alsa on a UDOO board that runs Ubuntu. The two interfaces
> are connected on the two USB 2.0 port available on the board: I'm not
> using any hub. In 20% of the cases, this works fine and I'm able to
> use the two interface as one single "virtual" interface with 4 inputs
> and 4 outputs (see my .asoundrc file bellow).

So the hardware actually supports the required bandwidth.

> However, in 80% of the cases, this doesn't work and dmesg says:
> "cannot submit datapipe for urb 0, error -28: not enough bandwidth".

Sounds like a bug in the USB controller driver of your board.