From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755316AbXLDPMY (ORCPT ); Tue, 4 Dec 2007 10:12:24 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753784AbXLDPML (ORCPT ); Tue, 4 Dec 2007 10:12:11 -0500 Received: from smtp4-g19.free.fr ([212.27.42.30]:54405 "EHLO smtp4-g19.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753863AbXLDPMK (ORCPT ); Tue, 4 Dec 2007 10:12:10 -0500 Message-ID: <47556E48.40703@free.fr> Date: Tue, 04 Dec 2007 16:12:08 +0100 From: John Sigler User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.0.8) Gecko/20061108 SeaMonkey/1.0.6 MIME-Version: 1.0 To: Dick Johnson CC: linux-kernel@vger.kernel.org, linux-pci@atrey.karlin.mff.cuni.cz Subject: Re: Is the PCI clock within the spec? References: <475532A7.1000408@free.fr> <20071204134254.5db8e27d@bull.net> <475555A6.3060202@free.fr> In-Reply-To: Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Dick Johnson wrote: > You can't just touch a scope-probe to the PCI > clock pin and clip the scope-probe grounding > lead to a convenient "ground" to make these > measurements! You need a special fixture that > will make a low-inductance connection to the > PCI bus in the same manner as the interface chip. (This is waaay over my head.) Why do you think the two plots (at least the second one) were not obtained as you describe? Why would the system manufacturer botch the measurements when I asked them to show me evidence that their system was compliant? > A scope probe will allow you to see if there is > a clock signal. That's all. You can't determine > its quality. A 4-inch ground lead on the scope > probe will result in 10-20% overshoot and undershoot > being observed. I don't understand this 10-20% figure. (0V + 10-20% is still 0V.) AFAIU, the nominal peak-to-peak voltage is 3.3V. The observed peak-to-peak voltage is 6.08V (3.3V + 84%). Regards.