Quote:
So I decide to send the modem a command (signal strength) as follows:
echo 'AT+CSQ' > dev/ttyUSB3
sierra ttyUSB2: sierra_open: submit urb 7 failed (-12) 4096
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I see that you are issuing AT command to "/dev/ttyUSB3" and getting error for "ttyUSB2". That seems odd to me. Could you please recheck the connection procedures.
URB- stands for USB request Blocks which is the basic data structure used for communication in USB protocol. So for any USB communication this is needed, without this USB transaction is impossible.
usb_submit_urb - This function actually submits the URB to the kernel for using it in USB communication. Since it is failing, it is not possible for communicate using USB protocol.
Hope this helps
Thanks,