Mass-market USB modems and the ZTE MF636

Way back when, I had a Huawei E220. This was moderately usable under Linux, more so after a firmware upgrade and usb_modeswitch. A great little device, installation of a long USB cable meant I could put the dongle where the signal was best. I still have it, although it’s likely locked to Vodafone.
For reasons unknown, the company I worked for ceased the contract on this and gave me a GlobeTrotter iCON 7.2 modem. Again, after some fiddling, success. The only problem was its shape – like a plastic ice lolly. It wiggled in whichever USB port I used it in, and I never really got on with it. However, it worked.
The iCON broke, and I now have a ZTE MF636. This is an aesthetically pleasing device, with one big flaw – it’s utter rubbishness under Linux.
I’ve spent a considerable amount of time battling these little gems:

  • ZeroCD support – great for Windows and Mac machines as your drivers are forced upon you. It can be turned off permanently with the AT+ZCDRUN=8 command (and turned on with AT+ZCDRUN=9), or ejecting the SCSI CD-ROM device.
  • option.ko support – of the four serial ports presented, ttyUSB3 (the final one) under Linux 2.6.32 is the only one accessible. I think I have a workaround.
  • modemmanager support – right now, I can’t dial out using NetworkManager. With wvdial, I can poke commands at ttyUSB3 and connect successfully, but that’s ugly in my eyes.
  • Random USB resetsreset high speed USB device using ehci_hcd and address 33 is not a welcome message, especially when I have to unplug and replug the USB device to get it to work again.

I’m not overly comfortable with delving down to the low level of these sorts of problems – but looking on the positive side, it’s a great learning experience. Yeah 🙂

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