From owner-freebsd-hackers  Wed Aug 22 21:49:10 2001
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Message-Id: <200108230449.f7N4n6W81268@harmony.village.org>
To: Poul-Henning Kamp <phk@critter.freebsd.dk>
Subject: Re: clock synchronization quality via NTP ? 
Cc: Thierry Herbelot <thierry@herbelot.com>, hackers@FreeBSD.ORG
In-reply-to: Your message of "Thu, 23 Aug 2001 06:43:26 +0200."
		<46651.998541806@critter> 
References: <46651.998541806@critter>  
Date: Wed, 22 Aug 2001 22:49:06 -0600
From: Warner Losh <imp@harmony.village.org>
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In message <46651.998541806@critter> Poul-Henning Kamp writes:
: In message <200108230242.f7N2gfW80510@harmony.village.org>, Warner Losh writes:
: 
: >: More precisely : is it reasonable to hope having a system clock not
: >: farther from the GPS clock by more than 50 micro-seconds ?
: 
: 50 microseconds should be feasible provided that you either
: provide a very stable temperature or replace the 14.318 MHz
: xtal on the motherboard with a something more stable.

Yea.  I just took a look at the data that we have, and we're seeing
more like +- 15us on machines here without temerpature stability
beyond "normal HVAC" and stock xtals on the motherboard.  This is
after we've done the fast interrupt hack.  Without it, the other
system activity was causing enough interrupt latncy variance that we
would see more like +- 80us with outliers way off in the weeds
(+- just under 10ms!).

Warner


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