[Soekris] USB power switching? (net4801/Linux)

[Bob Bishop]

On 5 May 2008, at 11:54, THORNTON Simon wrote:

> Hi,
>
> Just a thought but you could cut the 5V track connected to pin 1 of  
> the USB plug
> and insert a 5V normally closed (NC) relay between the USB connector  
> and the cut
> track. Drive the relay using one of the GPIO pins with a transistor  
> across the 5V
> power  rail of the soekris, make sure you put a diode across the  
> relay contacts.

Surely s/contacts/coil/ to protect the driver transistor from the back  
EMF when de-energising the coil?

> There are various simple relay driver circuits around that will do  
> this safely
> without damaging the GPIO chip.  To reset the USB device you turn on  
> the relay
> for 1 sec (cuts the power) then turn it off, the NC means that the  
> device will be
> powered on unless you energise the relay.
>
> Rgds,
>
> Simon
>
>
> -----Original Message-----
> From: soekris-tech-bounces at lists.soekris.com
> [mailto:soekris-tech-bounces at lists.soekris.com] On Behalf Of Randall  
> Nortman
> Sent: Sunday, May 04, 2008 22:09
> To: soekris-tech at lists.soekris.com
> Subject: [Soekris] USB power switching? (net4801/Linux)
>
> I have a remote system with a USB device that apparently is prone to
> locking up such that it needs to be power cycled (or unplugged and
> plugged back in).  A reboot of the system is not adequate to bring it
> back to life, because the device (apparently) retains power during the
> reboot.  Does the USB controller in the net4801 permit power to the
> devices to be switched off under software control?  And if so, do the
> Linux drivers support this?  I fear the answer is no to at least one
> of those questions, because lsusb -v shows this under the hub
> descriptor:
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--
Bob Bishop          +44 (0)118 940 1243
rb at gid.co.uk fax +44 (0)118 940 1295