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My Netgear WiFi stick (using the ath9k_htc driver) on my Raspberry Pi periodically gets into a bad state that results in USB read errors in dmesg. This state cannot be corrected by a system reset, but requires a full power cycle of the USB device, either by unplugging it and plugging the USB stick back in, or power cycling the whole computer.

I have read that it is possible to programmatically cycle power to a USB device using a USB hub. So I have tried this with my inland 4 Port USB 2.0 Hub based on the information in this posting:

http://stackoverflow.com/questions/1163824/linux-usb-turning-the-power-on-and-off

But the lights on the USB WiFi stick stay glowing even after issuing the command below, although it does make the wlan0 device disappear. I tried it on a Belkin 4-Port Hub with the same results. Anybody have any ideas?

echo '1-1.2.3' | tee /sys/bus/usb/drivers/usb/unbind

Details of my usb connections:

pi@fpi-16 ~ $ sudo lsusb -t
/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=dwc_otg/1p, 480M
    |__ Port 1: Dev 2, If 0, Class=hub, Driver=hub/3p, 480M
        |__ Port 1: Dev 3, If 0, Class=vend., Driver=smsc95xx, 480M
        |__ Port 2: Dev 4, If 0, Class=hub, Driver=hub/4p, 480M
            |__ Port 1: Dev 5, If 0, Class=vend., Driver=rt2800usb, 480M
            |__ Port 3: Dev 6, If 0, Class=vend., Driver=ath9k_htc, 480M
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1 Answer 1

If your USB host driver is compiled as a kernel module you can try to unload it and reload it. This should usually also power off totally the USB (I did it on other devices with faulty USB hardware that need to be electrically reset, not specifically on the Rasperry Pi which I don't have sorry). So check if you see it as a module (lsmod) or compile it as a module and later on rmmod it (and all the dependencies eventually) and reload it again, it should do the trick.

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