From owner-freebsd-current@FreeBSD.ORG Tue Jan 3 10:17:23 2006 Return-Path: X-Original-To: current@freebsd.org Delivered-To: freebsd-current@FreeBSD.ORG Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id B6A8116A41F for ; Tue, 3 Jan 2006 10:17:23 +0000 (GMT) (envelope-from PeterJeremy@optushome.com.au) Received: from mail07.syd.optusnet.com.au (mail07.syd.optusnet.com.au [211.29.132.188]) by mx1.FreeBSD.org (Postfix) with ESMTP id A585843D45 for ; Tue, 3 Jan 2006 10:17:22 +0000 (GMT) (envelope-from PeterJeremy@optushome.com.au) Received: from cirb503493.alcatel.com.au (c220-239-19-236.belrs4.nsw.optusnet.com.au [220.239.19.236]) by mail07.syd.optusnet.com.au (8.12.11/8.12.11) with ESMTP id k03AHDXT004457 (version=TLSv1/SSLv3 cipher=EDH-RSA-DES-CBC3-SHA bits=168 verify=NO); Tue, 3 Jan 2006 21:17:14 +1100 Received: from cirb503493.alcatel.com.au (localhost.alcatel.com.au [127.0.0.1]) by cirb503493.alcatel.com.au (8.12.10/8.12.10) with ESMTP id k03AHDHh046950; Tue, 3 Jan 2006 21:17:13 +1100 (EST) (envelope-from pjeremy@cirb503493.alcatel.com.au) Received: (from pjeremy@localhost) by cirb503493.alcatel.com.au (8.12.10/8.12.9/Submit) id k03AHDTL046949; Tue, 3 Jan 2006 21:17:13 +1100 (EST) (envelope-from pjeremy) Date: Tue, 3 Jan 2006 21:17:13 +1100 From: Peter Jeremy To: "M. Warner Losh" Message-ID: <20060103101713.GI42228@cirb503493.alcatel.com.au> References: <20060102.221046.75255380.imp@bsdimp.com> <20060103061752.GE42228@cirb503493.alcatel.com.au> <20060103.015516.21274860.imp@bsdimp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060103.015516.21274860.imp@bsdimp.com> User-Agent: Mutt/1.4.2.1i X-PGP-Key: http://members.optusnet.com.au/peterjeremy/pubkey.asc Cc: current@freebsd.org Subject: Re: FreeBSD handles leapsecond correctly X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 03 Jan 2006 10:17:23 -0000 On Tue, 2006-Jan-03 01:55:16 -0700, M. Warner Losh wrote: >In message: <20060103061752.GE42228@cirb503493.alcatel.com.au> > Peter Jeremy writes: >: Actually, I'd suggest that you can't build a system that keeps any >: sort of accurate time without a connection to the outside world or a >: quite substantial budget. If you assume a leap second every 5 years >: then the difference between UTC and TAI is about 6e-9 - being able > >Actually, that's wrong. If you assume a leap second every 18 months >you'd be better off, in the long run. That brings you into the high-end OCXO range I think - though I was thinking in terms of systems which needed to distinguish UTC and TAI without any external references. >: to tell the difference requires an atomic clock - which isn't common >: in embedded systems. > >Unless those embedded systems deal with time. Timing products are obviously a special case. I still stand by my "common" statement. >every time includes cases where the GPS reciever has been a powered >down spare for the past 9 months and therefore has no notion of the >leap seconds that have accumulated. This means it has to have an >extra long startup period while the GPS receive gets a new almanac. >This long wait is irritating to a customer, as you might imagine. In this case, the problem is that the connection to the outside world exists but does not provide the required information (UTC/GPS offset) in a timely manner. You could suggest that if the correct time is that critical to the customer, maybe they should be using hot-standby, not cold-standby spares :-). Does Galileo handle this any better? I now have a much better understanding of the background to your stance on leap seconds. -- Peter Jeremy