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I am connecting a Huawei E3131B USB 3G modem to my Beaglebone Black running Angstrom. When I connect it directly, the USB acts funny. Sometimes it picks up the modem, sometimes it dissapears from lsusb after a while (and loses power), and sometimes it does not pick it up at all. I need to make sure that it will have a stable connection with my board every time I start up.

How do I go about doing this? The problem occurs even if I don't hotplug.

One way I have got it to work is connecting it through a USB hub. When connected through the hub, it seems to work fine, but I cannot always have the hub present...

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Given the USB is likely powered I'd be a little suspicious of the power situation of this device when it's connected directly. You can begin to probe at these values using sudo lsusb -vvv.

Example

$ sudo lsusb -vvv -s "002:004" | less
...
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength           93
    bNumInterfaces          1
    bConfigurationValue     1
    iConfiguration          0 
    bmAttributes         0xa0
      (Bus Powered)
      Remote Wakeup
    MaxPower              100mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           3
      bInterfaceClass        11 Chip/SmartCard
      bInterfaceSubClass      0 
      bInterfaceProtocol      0 
      iInterface              0 
      ChipCard Interface Descriptor:
        bLength                54
        bDescriptorType        33
        bcdCCID              1.00
        nMaxSlotIndex           0
        bVoltageSupport         7  5.0V 3.0V 1.8V 
        dwProtocols             3  T=0 T=1
        dwDefaultClock       4000
        dwMaxiumumClock      4000
        bNumClockSupported      0
        dwDataRate          10752 bps
        dwMaxDataRate      500000 bps
        bNumDataRatesSupp.      0
        dwMaxIFSD             254
        dwSyncProtocols  00000000 
        dwMechanical     00000000 
        dwFeatures       00010230
...

Change the bus & device numbers (-s "002:004") for your situation. Also consult the lsusb man page for more on how to select pieces of the output.

Also I'd take a look at the output of dmesg when this issue occurs for futhre insight.

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