Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752492Ab0H0MZB (ORCPT ); Fri, 27 Aug 2010 08:25:01 -0400 Received: from earthlight.etchedpixels.co.uk ([81.2.110.250]:46307 "EHLO www.etchedpixels.co.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751620Ab0H0MY7 (ORCPT ); Fri, 27 Aug 2010 08:24:59 -0400 Date: Fri, 27 Aug 2010 13:41:54 +0100 From: Alan Cox To: Richard Cochran Cc: john stultz , Christian Riesch , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, devicetree-discuss@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, Krzysztof Halasa , Rodolfo Giometti , Arnd Bergmann Subject: Re: [PATCH 1/5] ptp: Added a brand new class driver for ptp clocks. Message-ID: <20100827134154.50eef56c@lxorguk.ukuu.org.uk> In-Reply-To: <20100827075727.GA3818@riccoc20.at.omicron.at> References: <363bd749a38d0b785d8431e591bf54c38db4c2d7.1281956490.git.richard.cochran@omicron.at> <20100817085324.GB3330@riccoc20.at.omicron.at> <1282090963.1734.97.camel@localhost> <20100818071942.GA4096@riccoc20.at.omicron.at> <1282176776.2865.100.camel@localhost.localdomain> <20100819055518.GA4084@riccoc20.at.omicron.at> <1282594125.3111.344.camel@localhost.localdomain> <1282874269.4371.74.camel@localhost.localdomain> <20100827075727.GA3818@riccoc20.at.omicron.at> X-Mailer: Claws Mail 3.7.6 (GTK+ 2.18.9; x86_64-redhat-linux-gnu) Face: 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 Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1198 Lines: 28 > The master node in a PTP network probably takes its time from a > precise external time source, like GPS. The GPS provides a 1 PPS > directly to the PTP clock hardware, which latches the PTP hardware > clock time on the PPS edge. This provides one sample as input to a > clock servo (in the PTPd) that, in turn, regulates the PTP clock > hardware. A PTP clock is TAI, Unix time is UTC. > This is the core issue and source of misunderstanding, in my view. The > fact of the matter is, the current generation of computers has > multiple clocks, and these are usually unsynchronized. I think we > should not try too hard to cover up or work around this. It is a fact > of life. In this case I don't think you can. Their divergence is rather difficult to handle unless you have a GPS to hand. But all this talk of "PTP this" and "PTP that" is not helpful. Any interface for additional time sources should be generic with PTP being one use case. Alan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/