Date: Sat, 27 Oct 2001 00:20:52 +0200 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: Julian Elischer <julian@elischer.org> Cc: Matthew Dillon <dillon@apollo.backplane.com>, John Baldwin <jhb@FreeBSD.ORG>, arch@FreeBSD.ORG, Peter Wemm <peter@wemm.org>, Bakul Shah <bakul@bitblocks.com> Subject: Re: 64 bit times revisited.. Message-ID: <613.1004134852@critter.freebsd.dk> In-Reply-To: Your message of "Fri, 26 Oct 2001 16:25:09 PDT." <Pine.BSF.4.21.0110261622450.11653-100000@InterJet.elischer.org>
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In message <Pine.BSF.4.21.0110261622450.11653-100000@InterJet.elischer.org>, 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 :-) -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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