From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <4C7A6164.60208@riesch.at> Date: Sun, 29 Aug 2010 15:32:20 +0200 From: Christian Riesch MIME-Version: 1.0 To: Alan Cox Subject: Re: [PATCH 1/5] ptp: Added a brand new class driver for ptp clocks. 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> <20100827134154.50eef56c@lxorguk.ukuu.org.uk> In-Reply-To: <20100827134154.50eef56c@lxorguk.ukuu.org.uk> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: Rodolfo Giometti , Arnd Bergmann , john stultz , Richard Cochran , linux-kernel@vger.kernel.org, Christian Riesch , netdev@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, devicetree-discuss@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, Krzysztof Halasa List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Alan Cox wrote: >> 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. Not necessarily. AFAIK, the time distributed by IEEE1588v2 can either be based on the "PTP epoch" (timePropertiesDS.ptpTimescale=TRUE) and thus represent TAI or be based on an implementation specific arbitrary epoch (timePropertiesDS.ptpTimescale=FALSE) and represent time on some arbitrary time scale. Christian