From owner-freebsd-usb@FreeBSD.ORG Tue Jul 11 06:05:15 2006 Return-Path: X-Original-To: freebsd-usb@freebsd.org Delivered-To: freebsd-usb@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 4F4F616A4DD for ; Tue, 11 Jul 2006 06:05:15 +0000 (UTC) (envelope-from imp@bsdimp.com) Received: from harmony.bsdimp.com (vc4-2-0-87.dsl.netrack.net [199.45.160.85]) by mx1.FreeBSD.org (Postfix) with ESMTP id 943AD43D45 for ; Tue, 11 Jul 2006 06:05:14 +0000 (GMT) (envelope-from imp@bsdimp.com) Received: from localhost (localhost.village.org [127.0.0.1] (may be forged)) by harmony.bsdimp.com (8.13.4/8.13.4) with ESMTP id k6B62E3w031913; Tue, 11 Jul 2006 00:02:14 -0600 (MDT) (envelope-from imp@bsdimp.com) Date: Tue, 11 Jul 2006 00:02:22 -0600 (MDT) Message-Id: <20060711.000222.-432839116.imp@bsdimp.com> To: gcorcoran@rcn.com From: "M. Warner Losh" In-Reply-To: <44B2FB8A.7010104@rcn.com> References: <200607101326.17709.frank@barda.agala.net> <20060710.084321.155333942.imp@bsdimp.com> <44B2FB8A.7010104@rcn.com> X-Mailer: Mew version 4.2 on Emacs 21.3 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-2.0 (harmony.bsdimp.com [127.0.0.1]); Tue, 11 Jul 2006 00:02:14 -0600 (MDT) Cc: freebsd-usb@freebsd.org Subject: Re: Lowering USB Transfer Rate? X-BeenThere: freebsd-usb@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: FreeBSD support for USB List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 11 Jul 2006 06:05:15 -0000 In message: <44B2FB8A.7010104@rcn.com> Gary Corcoran writes: : M. Warner Losh wrote: : > In message: <200607101326.17709.frank@barda.agala.net> : > "Frank J. Beckmann" writes: : > : there is no difference in cables between USB 1.1 and 2.0. Only special low : > : speed cable for low speed devices may be different. : > : > Actually, there *IS* a difference between 1.1 and 2.0 cables. The : > plugs on the ends are the same, however. The problem is that you can : > get data dropouts using 1.1 cables to get 2.0 speeds. : : Ummm - I thought one of the design goals of USB 2.0, which Intel : *knew* they were going to do while USB 1.x was coming out, was to be : able to use _exactly_ the same cables. Which is why they specified : such good, braided full shielding cables, were required for USB 1.x. : And why they didn't change the connector - because the (unknowing) : consumer then wouldn't have to worry about whether they had the : "right" cable. If they really were intended to be different, : wouldn't they have changed the connector? The cables are different. 2.0 certified cables definitely are required to work at 2.0 speeds. I've had problems with certain designs where 2.0 cables worked, and 1.1 didn't. It is an absolute fact. I don't have my copies of usb 2.0 standard handy, but there's a section in it that addresses this issue. That's why cables for a while came out with 2.0 certified on them. : Of course as Frank alluded to, there may have been some unscrupulous : manufacturers making el-cheapo cables, which they knew they could : get away with for low speed USB 1.x devices. Is that what you were : referring to, Warner? Or what (specifically) are you talking about? When 1.0 came out, the specs were very loose. In anticipation of 2.0, the standards were tightened (maybe in time for 1.1), and new cables started to appear on the market. But since 1.1 cables were cheaper to make, they were cheaper in the marketplace and persisted until 2.0 devices became ubiquitous. I have several of these cables, and they are utterly useless with 2.0 devices. : But as far as I know, general, well shielded USB cables, from reputable : manufacturers, should be usable for USB 2.0, even if they were manufactured : during the USB 1.x days. It's easiest to tell with the clear jacket cables : showing you the full braided shielding... ;-) Well shielded usb cables are likely certified 2.0. The older cables aren't shielded, and are the ones to which I'm referring to. They definitely do not work at usb 2.0 speeds. Warner