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I have a composite USB device that emulates a sound card and a serial port. The sound card portion works as expected, however I am having trouble trying to communicate with the COM port of this device. The issue seems to be that the com port is not being assigned (or I don't understand how it is being assigned). Running dmesg yields the following info regarding this device when plugged into the port:

01  [   55.328014] usb 8-2: new full-speed USB device number 2 using uhci_hcd

02  [   55.497033] usb 8-2: New USB device found, idVendor=1fc9, idProduct=400f

03  [   55.497038] usb 8-2: New USB device strings: Mfr=1, Product=2, SerialNumber=3

04  [   55.497042] usb 8-2: Product: TONE GENERATOR+CDC

05  [   55.497045] usb 8-2: Manufacturer: CIE Engineering Inc Tgen4

06  [   55.497048] usb 8-2: SerialNumber: 0001

07  [   55.528800] usbcore: registered new interface driver snd-usb-audio

08  [   55.529499] cdc_acm: probe of 8-2:1.2 failed with error -22

09  [   55.529526] usbcore: registered new interface driver cdc_acm

10  [   55.529529] cdc_acm: USB Abstract Control Model driver for USB modems and ISDN adapters

I’ve added ‘line numbers’ to the log above for reference.

Line 01:the new device being plugged in to USB bus 8 device 2.

Lines 02-06: various config info for the card

Line 07: recognition of the virtual ‘sound card’

Line 08 shows an error with the virtual com port (cdc_acm)

Line 09 shows the registration of a new virtual com port

Line 10 shows the ACM driver load.

The error message shown in line 8 is 'EINVAL' or an 'invalid argument', but lines 9 and 10 seem to indicate that a driver was 'registered'. The behavior I was hoping for was that a com port would be assigned @ ttyACM0 but that doesn't happen. Examining the com ports before and after the device's insertion shows no new tty* ports.

The OS is Ubuntu 14.04.5 LTS.

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