HOWTO: Initializing an CDC ECM LTE modem using raw USB messages

[wrobelda]

I was struggling with getting Huawei E3131 modem initialize under FreeBSD/OPNSense in CDC ECM mode, even though it worked out-of-the-box with Linux and NetworkManager. What NetworkManager actually does is and equivalent of a simple:

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echo -e 'AT^NDISDUP=1,1\r' > /dev/cdc-wdm0
sent to the WDM device CDC WDM control interface. Sending this to any of the serial diagnostic or PPP serial ports would *not* work, it has to be sent to WDM interface explicitly.

Unfortunately, FreeBSD/OPNSense does not have module for WDM and as such doesn't expose the cdc-wdm character device like Linux. The workaround here was using usbcontrol to send the USB control message directly to the device, like so:

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usbconfig -d 8.2 -i 0 do_request 0x21 0 0 2 16 0x41 0x54 0x5e 0x4e 0x44 0x49 0x53 0x44 0x55 0x50 0x3d 0x31 0x2c 0x31 0x0d 0x0a
REQUEST = <OK>
Where,

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-d 8.2 -i 0 do_request 0x21 0 0 2 16 instructs usbconfig to send a control message of length 0x16 to device at bus 8.2, while the

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0x41 0x54 0x5e 0x4e 0x44 0x49 0x53 0x44 0x55 0x50 0x3d 0x31 0x2c 0x31 0x0d 0x0a is the byte-encoded "AT^NDISDUP=1,1\r\n" message.

I explained my findings in details in an article here, hopefully this will help others having similar issue:
https://dawidwrobel.com/journal/initializing-lte-modem-using-raw-usb-communication/

[cookiemonster]

This is pretty nice work. I have no use for it but thanks for sharing @wrobelda.

[wrobelda]

This is pretty nice work. I have no use for it but thanks for sharing @wrobelda.

Thanks, hopefully this will be of help for someone, given how many people appear to have struggled with a similar issue.