Re: USB power usage during startup (was: CVS commit: src/sys/dev/usb)

[jnemeth%victoria.tc.ca@localhost (John Nemeth)]

On Jun 17,  8:14am, Tobias Nygren wrote:
} On Fri, 25 Jan 2008 13:25:01 +0100
} > On Fri, Jan 25, 2008 at 12:29:12AM +0000, Jared D. McNeill wrote:
} > > 
} > > Module Name:      src
} > > Committed By:     jmcneill
} > > Date:             Fri Jan 25 00:29:12 UTC 2008
} > > 
} > > Modified Files:
} > >   src/sys/dev/usb: uhub.c
} > > 
} > > Log Message:
} > > Speed up uhub attachment considerably. Rather than powering up each port
} > > individually then waiting for it to become stable, power them up all
} > > at once and then delay. Don't even bother delaying if we are a root hub,
} > > as this is handled separately in the event thread. From OpenBSD.
} > 
} > Hmm, how much power does this consume if you have more then one usb device
} > which needs a lot of power during startup?
} 
} USB devices must negotiate with the hub for more power than 0.5W.
} If they draw more, even during startup, they violate the spec.

    0.5W or 100 mA.  See:  http://en.wikipedia.org/wiki/Usb#Power

}-- End of excerpt from Tobias Nygren