Information on XO-1 power efficiency

david at david at
Wed Nov 18 00:41:23 EST 2009

On Tue, 17 Nov 2009, John Gilmore wrote:

>> Is USB device discover inherently slow?  Or is the sloth just handling
>> strange cases?  Can I speed things up if I only need to verify that devices I
>> knew about are still there?
> Bringing up the USB bus is apparently *designed* to take a large
> fraction of a second.  After you turn on USB bus power, you have to
> wait for X hundred milliseconds for the power to stabilize and for any
> devices to come out of power-on reset.  Ditto after you turn on USB
> signalling.

I seem to remember a discussion on linux-kernel about USB startup. 
historicly it waited 500ms (half a second) to allow devices to startup. 
there was apparently an attempt to shorten this to 100ms to speed up boot 
and people reported issues with devices not being detected. apparently 
it's highly dependant on the exact devices that you have, some are MUCH 
faster than others.

David Lang

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