From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750952AbWFAXg2 (ORCPT ); Thu, 1 Jun 2006 19:36:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750958AbWFAXg2 (ORCPT ); Thu, 1 Jun 2006 19:36:28 -0400 Received: from shawidc-mo1.cg.shawcable.net ([24.71.223.10]:4814 "EHLO pd4mo1so.prod.shaw.ca") by vger.kernel.org with ESMTP id S1750952AbWFAXg1 (ORCPT ); Thu, 1 Jun 2006 19:36:27 -0400 Date: Thu, 01 Jun 2006 17:35:22 -0600 From: Robert Hancock Subject: Re: USB devices fail unnecessarily on unpowered hubs In-reply-to: <6iX82-2UJ-3@gated-at.bofh.it> To: linux-kernel Message-id: <447F79BA.4090904@shaw.ca> MIME-version: 1.0 Content-type: text/plain; charset=ISO-8859-1; format=flowed Content-transfer-encoding: 7bit References: <6iWP5-2gj-71@gated-at.bofh.it> <6iX82-2UJ-3@gated-at.bofh.it> User-Agent: Thunderbird 1.5.0.2 (Windows/20060308) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org 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/