usb disconnect/reconnect issue


I am having issues with my usb hub disconnecting then connecting at what
appears to be random intervals.

Here is my setup:

Beagle board rev b4
Digitus 4 port usb hub
linksys usb200m (usb->ethernet)

Here is the error message I get:

Hi Ben,

I'm having the same problem but with a B5 board so not sure this issue
is confined to B4.

My setup:

    - Digitus 4-port powered USB hub (as supplied by Digikey)
    - Linksys USB200M Ethernet adapter
    - USB keyboard & mouse

For me, this happens every 30s to 2 mins causing my network link to go
down - a real pain.

I found the following posting which sounds promising:

...but not sure whether this could solve your problem if you've got
the same kernel on both boards.

Anyway, I'll give it a go and let you know how I got along.




I had problems with a Digitus 7-port hub from DIgikey. It would crash on insertion/removal of certain devices - usb thumb drive, but worked with others. I thought the problem was USB software related, but then I switched USB hubs to a Linksys 4-port hub, USB2HUB4 and the insertion/deletion and not recognizing certain devices went away. So maybe some of other problems people are having with USB are related to specific USB hubs.


The problem might be related to how different hubs handle hot
swapping. Basically, when you plug in a USB device, the hub must
charge a large bypass capacitor in the device. If you don't do
something special, this requires a large quantity of charge to
transfer from the hub's bypass capacitor to the device's, causing the
hub's +5V to dip momentarily.

The proper way to deal with this is for a hub to have "soft start"
circuitry that charges the USB device slowly (i.e., in milliseconds
instead of microseconds) so that the USB's +5V supply doesn't dip. I
don't know if USB has a standard on this or it's just that some hubs
do this better than others.

This is all a guess based on elementary circuit theory, not an
analysis of actual hardware.