Date: Sat, 30 Mar 2002 09:28:59 -0500 From: Leo Bicknell <bicknell@ufp.org> To: Paul Halliday <dp@penix.org> Cc: hackers@FreeBSD.ORG Subject: Re: GPS time. Message-ID: <20020330142859.GA19243@ussenterprise.ufp.org> In-Reply-To: <Pine.LNX.4.43L0.0203291757560.4473-100000@saruman.xwin.net> References: <Pine.LNX.4.43L0.0203291757560.4473-100000@saruman.xwin.net>
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In a message written on Fri, Mar 29, 2002 at 06:04:11PM -0600, Paul Halliday wrote:
> I just connected my gps (garmin gps III plus) to my serial port
> and realized that simply cat'ing cua0 displays date/time/position of the
> unit. (neato). Anyway, how accurate would it be to use the time from this
> output for ntp as opposed to my current setup using ntp servers.
Your NTP servers are better.
I tested a III Plus, and without a 1 PPS source (which that model
doesn't provide) it's accurate to about 100ms, give or take. Since
real NTP servers are < 1ms, they really aren't that good. It's
not that the time isn't accurate, it's that they were not designed
to communicate with that accuracy to an external device.
If you NTP off the Internet, and want a local backup clock it might
be an acceptable solution. However clocks that can achieve < 1ms
accuracy can be had for < $1000, so if you really care you should
get one of those.
You might want to do some searches for NTP in google.
--
Leo Bicknell - bicknell@ufp.org - CCIE 3440
PGP keys at http://www.ufp.org/~bicknell/
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