the linux kernel did create a file /dev/ttyACM0, but any access will lock system for several seconds(permission is correct). And then check the kernel log, you'll find some usb low-level timeout event.
So I think the main firmware on AVR32 has some bug, let the usb device not a standard one.
Try opening the port with a standard serial terminal program such as PuTTY - that should set the baud rate (while directly cat'ing to /dev/ttyACM0 won't). The device firmware may time out unless the port settings are indicated beforehand.
- Dean :twisted: