2

I am trying to connect 4 3G dongles to Raspberry Pi B+, I have some troubles making them all reply to AT commands, and I see that each time I connect one dongle, 3 new /dev/ttyUSBx ports are created in /dev

Is this normal ? Shouldn't I see just one port there? I feel that I am reaching some limitations when I have 4 dongles and 12 ports there. Only 3 unique devices reply to AT commands.

I connected them trough a 4 port hub.

The lsusb -t output:

/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=dwc_otg/1p, 480M
|__ Port 1: Dev 2, If 0, Class=hub, Driver=hub/5p, 480M
    |__ Port 1: Dev 3, If 0, Class=vend., Driver=smsc95xx, 480M
    |__ Port 3: Dev 4, If 0, Class=hub, Driver=hub/4p, 480M
        |__ Port 1: Dev 5, If 0, Class=vend., Driver=option, 480M
        |__ Port 1: Dev 5, If 1, Class=vend., Driver=option, 480M
        |__ Port 1: Dev 5, If 2, Class=vend., Driver=option, 480M
        |__ Port 2: Dev 6, If 0, Class=vend., Driver=option, 480M
        |__ Port 2: Dev 6, If 1, Class=vend., Driver=option, 480M
        |__ Port 2: Dev 6, If 2, Class=vend., Driver=option, 480M
        |__ Port 3: Dev 7, If 0, Class=vend., Driver=option, 480M
        |__ Port 3: Dev 7, If 1, Class=vend., Driver=option, 480M
        |__ Port 3: Dev 7, If 2, Class=vend., Driver=option, 480M
        |__ Port 4: Dev 8, If 0, Class=vend., Driver=option, 480M
        |__ Port 4: Dev 8, If 1, Class=vend., Driver=option, 480M
        |__ Port 4: Dev 8, If 2, Class=vend., Driver=option, 480M
1
  • Please provide a model number for the dongle. It's probably providing multiple endpoints for various functions.
    – Doug Edey
    Commented Apr 12, 2015 at 0:08

1 Answer 1

1

Linux supports having a very large number of tty devices in /dev/ (each time you open another xterm or tmux window tty devices are created, ever left a laptop running and ended up with 100s of xterm windows across multiple workspaces?). USB (and the linux USB implementation) also supports a fairly large number of connected devices. I would assume the reason you are having issues with the 4th modem is because the hub can't supply enough power to 4 modems at once (3g modems use a lot of power).

1
  • Yes, I think it was a power issue, it worked eventually but power led blinks (indicating low power). I used ports 0,3,6,9, but I am curious why 3 exact ports for each one GSM dongle.
    – adrianTNT
    Commented Nov 14, 2014 at 3:23

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.