Subject: Re: soft control of +5V at a USB hub port?
To: J Chapman Flack <email@example.com>
From: Lennart Augustsson <firstname.lastname@example.org>
Date: 05/04/2005 19:55:27
It depends on the hub if you can control power to the port
individually. But my guess is that it doesn't monitor the
+5V, but instead checks if the port is enabled. You can
always enable&disable ports individually. But there is no
way to do this from outside the kernel at the moment.
J Chapman Flack wrote:
> Here's something I've been wondering for a while:
> I have a USB scanner. It gets its power from an independent wall wart,
> and it has no power switch. It does go into a powered-down mode when
> the computer is off, though, and I can make it do that by unplugging the
> USB cable. Apparently the scanner, even though it is independently powered,
> watches the +5V on the USB cable and powers down when that drops.
> I would like to be able to keep the scanner powered down the vast majority
> of the time when I am not using it at all. I have heard just enough about
> the inner workings of USB to wonder if it's possible on some or all USB hubs
> to command down the +5V on a particular port through software. Whether
> there's driver support is another question - right now I'm just curious if
> anyone who knows USB better than I do thinks the idea is even possible.