Hi

I am writing a Perl script that detects USB 3G modem (of various types), switches it and then creates a connection with the ISP provider.

My problem is that several /dev/ttyUSB* files are created, and most cannot be used to connect.
I managed to filter some out by using modem command such as "at+csq" or "ati" (I receive a "timeout" on unconnected ttyUSBs).
But in some cases I am left with more than one /dev/ttyUSB* that respond correctly to these commands, but only one ttyUSB will actually work correctly with pppd.

For a more concrete example: USB stick Alcatel X220 (Vendor 1bbb product 0017). Both ttyUSB3 and ttyUSB4 respond to ati commands, but only ttyUSB4 will actually create the ppp connection (on ttyUSB3 pppd sends configuration requests but no answers are received).

Is there a way I can find out which ttyUSB is usable through a script?
This way should be generic for all USB modem types

The only way I can think of now is to add specific udev rules for ALL supported USB modems. And every time we add another supported modem, to add another rule.
Will be very thankful if there is an easier way to find out which ttyUSB to use

Thank you
Karin

Have you tried using lsusb to locate the right one?.

Can you please elaborate?
lsusb returns "Bus 001 Device 003: ID 1bbb:0017"

How can I use this output to locate the correct /dev/ttyUSB*?

(I understand it helps me locate the /proc/bus/usb file that I can use for usbreset, but how else can I use this?)

Thank you
Karin

Is /dev/ttyUSB* a file or a link to a file in /dev/bus/usb/00?

If it is not a link then maybe you can get the information you need from dmesg, otherwise you can use udev rules (create your own in /dev/udev/rules.d) to map your device to the same filename when connected to the system.

You will have to read de documentation to create your own rule (check this link), but you can also look inside the ones already created by the system (the one for the CD could help) and you will get a notion about how you should create your own.

/dev/ttyUSB* are files and not symbolic links
Also dmesg offers no help

I guess I will have to create a rule for each supported modem type (sadly - a few hundreds... :-( ). I guess I will create a script for that ... ;-)

Thank you for your help
K