On Fri, 11 Mar 2005, abcd efgh wrote:
> >Lack of power switching implies that the hub follows the USB 1.0 standard,
> >but since it is high speed it actually follows the USB 2.0 standard.
> >Also, overcurrent protection may be omitted only for bus-powered hubs.
> >Clearly the value is wrong.
>
> Is power switching a must for USB 2.0? I'm confused here.
Yes it is. See Table 11-13 in the USB 2.0 spec. In the description of
the two low-order bits it says:
1X: Reserved. Used only on 1.0 compliant hubs that implement no
power switching
> What I did was, I modified the wHubCharacteristics that was read from the
> device to a value that I constructed after reading the specs (1010 1001).
> How exactly is this value obtained from the device? I know it's not stored
> in the device. Is it related to the problems with the power supply to the
> board?
The value _is_ obtained from the device. But I don't know anything about
the specifics of your hardware. The change you made was important because
of those two low-order bits; you changed it from no power switching to
individual port power switching. So without the change the hub driver
would not turn on power to any of your hub's ports, but with the change it
would.
Alan Stern
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