MR3020 v3 + 3G Modem

Hello everybody

I flashed a MR3020 v3 with a Openwrt snapshot and then installed (using opkg) the packets Lua, Luci and those for usb and 3g support.

Luci, WiFi and ethernet is working ok but 3G modem doesn't. The mode is a Huawei E303.
When plugged, /dev/ttyUSB0 , /dev/ttyUSB1 and /dev/ttyUSB2 are created but the 3g Interface does not go up. At Luci interface, it shows "Error: network device is not present"

Could anyone help me?

Hello! Have you solved that?

I have a similar problem with router Asus AC51U and dongle USB MF821D. It seems that the USB device resets from time to time and the driver cannot recreate the entry in use by openwrt in /dev.
In my case, it also creates three devs (ttyUSB[0-2]). At first, to make it work I had to manually select ttyUSB2 in the interface configuration. Whenever a USB reset happens, a ttyUSB3 device is created, and I have to go into the interface configuration and select it. This is annoying...

Any hints on how to solve that?

Thank you!

I can't speak to this from any direct experience, but it sounds like it could be a power issue (i.e. the USB port on the router doesn't provide enough power to the modem). Try the following:

  • If the USB MF821D has an external power socket, try using that power input (presumably via an AC power adapter).
  • Try connecting a powered USB hub between the MF821D and the AC51U.

Thanks for your reply, @psherman!

I would not suspect that because the router is advertised/sold as a solution for WiFi networks with 3G/4G uplinks. I will try to get a hub to test it, anyway.

Nevertheless, that solves the reset (if it is the actual cause of the problem) but not the configuration issue.

Regarding the configuration issue -- I assume you're talking about the dev ttyUSB[0-2] issues... if the resets are related to a power issue, a more robust power supply will likely solve the enumeration problems you are seeing.

Basically, in a normal situation, each new device that is detected will be enumerated with the next ttyUSBx value. So if you plug in a second USB device, it would show up as ttyUSB1.

If a USB device suddenly goes offline (i.e. resets or is unplugged), it can take a little while for the linux kernel to purge the ttyUSBx entry associated with that device. So similar to the 2 device situation, if you unplug the device using ttyUSB0 and rapidly plug in a new device (only one USB device connected at a time), the new device may show up as ttyUSB1. But if you waited some time between the two devices (not sure how long purging takes), the new device would probably be enumerated as ttyUSB0.

Therefore, if there is a brief interruption due to power, the USB device may request enumeration as it comes back up and the linux kernel may issue the next number.