From owner-freebsd-arch Mon Oct 29 21: 9:32 2001 Delivered-To: freebsd-arch@freebsd.org Received: from rover.village.org (rover.bsdimp.com [204.144.255.66]) by hub.freebsd.org (Postfix) with ESMTP id D328637B401 for ; Mon, 29 Oct 2001 21:09:28 -0800 (PST) Received: from harmony.village.org (harmony.village.org [10.0.0.6]) by rover.village.org (8.11.3/8.11.3) with ESMTP id f9U59RV02463; Mon, 29 Oct 2001 22:09:27 -0700 (MST) (envelope-from imp@harmony.village.org) Received: from harmony.village.org (localhost [127.0.0.1]) by harmony.village.org (8.11.6/8.11.6) with ESMTP id f9U59Q701756; Mon, 29 Oct 2001 22:09:26 -0700 (MST) (envelope-from imp@harmony.village.org) Message-Id: <200110300509.f9U59Q701756@harmony.village.org> To: Poul-Henning Kamp Subject: Re: 64 bit times revisited.. Cc: arch@FreeBSD.ORG In-reply-to: Your message of "Sat, 27 Oct 2001 00:20:52 +0200." <613.1004134852@critter.freebsd.dk> References: <613.1004134852@critter.freebsd.dk> Date: Mon, 29 Oct 2001 22:09:26 -0700 From: Warner Losh Sender: owner-freebsd-arch@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG In message <613.1004134852@critter.freebsd.dk> Poul-Henning Kamp writes: : In message , Ju : lian Elischer writes: : >trouble is, that ticks are: : >1: not guaranteed to be constant : >2/ inaccurate. : > : >also, : >you can represent ticks in terms of 1/(2^64) units, certainly to the : >accuracy of the crystals that we use for timekeeping at this time. : : The 1/(10^9 * 2^32) resolution we have now would allow us to track : the NIST Cesium fountain with about a factor of at least 50 to : spare (we're still not sure just how good the fountain actually : is: what do you compare the worlds best clock to ? :-) : : 1/(2^64) would increase that to a safety factor of at least 185. : : I have successfully been able to measure the effect of turning my : HP5061 Cesium 90 degrees using our current code (changes the direction : of the earths magnetic field on the cesium beam), and that is an : effect down in the 1/10^14 range. : : I'm pretty sure no crystal will give you any trouble :-) Xtals in PCs SUCKSUCKSUCKSUCK. They are accurate to a factor of 1E-8 or so. This is >> 1/(2^64). When something drifts a second or two a day (or even a week or a month), you know it is really bad. Warner To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message