Re: USB devices fail unnecessarily on unpowered hubs

[Robert Hancock]

linux-os (Dick Johnson) wrote:
> Many, most, perhaps all such devices don't take more power when they
> are "enabled". Everything is already running and sucking up maximum
> current when you plug it in! If the motherboard didn't smoke when
> the device was plugged in, you might just as well let the user use
> it! Perhaps a ** WARNING ** message somewhere, but by golly, they
> got it running or else you wouldn't be able to read its parameters.

Wrong.. USB devices are not allowed to draw more than some amount (100 
mA I think) of power before the host tells it that it is allowed to 
switch into full-power mode. Any device that doesn't do this doesn't 
comply with the USB specs. Therefore it is very possible to connect a 
device and discover that it can't be enabled.

--
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@xxxxxxxxxxxxx
Home Page: http://www.roberthancock.com/

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