From: Robert Hancock <hancockr@shaw.ca>
To: linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: USB devices fail unnecessarily on unpowered hubs
Date: Thu, 01 Jun 2006 17:35:22 -0600 [thread overview]
Message-ID: <447F79BA.4090904@shaw.ca> (raw)
In-Reply-To: <6iX82-2UJ-3@gated-at.bofh.it>
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@nospamshaw.ca
Home Page: http://www.roberthancock.com/
next parent reply other threads:[~2006-06-01 23:36 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <6iS8y-35Z-5@gated-at.bofh.it>
[not found] ` <6iWP5-2gj-71@gated-at.bofh.it>
[not found] ` <6iX82-2UJ-3@gated-at.bofh.it>
2006-06-01 23:35 ` Robert Hancock [this message]
2006-06-01 23:46 ` USB devices fail unnecessarily on unpowered hubs Randy.Dunlap
[not found] ` <6iYxg-53W-29@gated-at.bofh.it>
[not found] ` <6j5oR-7Sw-11@gated-at.bofh.it>
2006-06-02 2:39 ` [linux-usb-devel] " Robert Hancock
[not found] <6kl8h-1Uf-15@gated-at.bofh.it>
2006-06-07 0:51 ` Robert Hancock
2006-06-05 11:07 Lee Dowling
-- strict thread matches above, loose matches on Subject: below --
2006-06-02 15:11 [linux-usb-devel] " Alan Stern
2006-06-02 19:49 ` David Liontooth
[not found] <6iYGP-5hv-3@gated-at.bofh.it>
[not found] ` <6iYQx-5Jc-7@gated-at.bofh.it>
2006-06-01 23:37 ` Robert Hancock
2006-06-01 9:18 David Liontooth
2006-05-30 20:01 ` Pavel Machek
2006-06-03 9:29 ` Oliver Neukum
2006-06-01 10:01 ` Andrew Morton
2006-06-01 11:42 ` Daniel Drake
2006-06-01 14:58 ` Alan Stern
2006-06-01 15:09 ` linux-os (Dick Johnson)
2006-06-01 15:23 ` Lennart Sorensen
2006-06-01 21:39 ` Dagfinn Ilmari Mannsåker
2006-06-01 15:53 ` Oliver Neukum
2006-06-01 17:24 ` linux-os (Dick Johnson)
2006-06-01 16:57 ` Alan Stern
2006-06-01 16:59 ` Andrew Morton
2006-06-01 17:08 ` Alan Stern
2006-06-01 17:34 ` Mark Lord
2006-06-01 17:47 ` Alan Stern
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