Re: PXA27x UDC Power

[Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>]

On Wed, 28 Nov 2007, Justin Clacherty wrote:

> > You get connected to a host ... the host chooses a configuration
> > it can support.
> I thought that was the case.  My real concern was that I wasn't sure 
> multiple configurations worked properly on the pxa27x.  The pxa27x 
> doesn't seem to like having RNDIS enabled and as far as I can recall it 
> is something to do with the strange way Intel implemented the 
> configurations.  I may have misinterpreted the problem though.

You don't have to worry about this.  Set up only one configuration,
with the 500 mA current requirement.  If the bus can't supply that much
power then the host will leave your gadget unconfigured, that is, it
will never send a Set-Config request.

The USB spec requires that all devices must draw no more than 100 mA 
while in an unconfigured state (more precisely, the DEFAULT or ADDRESS 
states).

Alan Stern


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