From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4B166A5B.6030400@domain.hid> Date: Wed, 02 Dec 2009 14:23:39 +0100 From: Gilles Chanteperdrix MIME-Version: 1.0 References: <4B1663B9.8030306@domain.hid> In-Reply-To: <4B1663B9.8030306@domain.hid> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-core] Realtime gettimeofday() List-Id: Xenomai life and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Wolfgang Mauerer Cc: xenomai@xenomai.org Wolfgang Mauerer wrote: > Hi, > > we'd like to implement a gettimeofday() mechanism that works > in realtime context, both from user- and kernelland. Most importantly, > the correctins made to the wall time by the NTP protcol on Linux > must be transferred into the Xenomai domain. Yes, the real issue is NTP, because other than that, you can simply implement gettimeofday in terms of clock_gettime(CLOCK_REALTIME). This issue has been discussed several times, but never a lot. We have a simple solution: starting with 2.4 (if I remember correctly) xenomai provides clock_settime, so you can simply rely on clock_gettime, and call clock_settime from time to time to resync the Xenomai clock with Linux NTP-enhanced clock. This is not pretty, you get a drift increasing over time, then suddenly been reset. But I guess this has been enough for current users, until now. You control the maximum drift by how often you call clock_settime. Would not it be enough for your use of xenomai? -- Gilles