In article ],
isw wrote:

Functionally impossible. By adding money, you can reduce the drift rate
but you can't make it zero. Period. Just use NTP.

Or, if you prefer something stand-alone which will give you a good time
reference if your network connection is down: use GPS.

It's not hard to find a GPS receiver which has a decent "pulse per
second" output on its serial port, as well as standard NMEA sentences.
Software packages are available which will monitor the NMEA output and
the PPS signal, and synchronize your PC's clock very accurately.

The better receivers (those specifically intended for timing purposes)
synchronize the PPS pulse edge with the start-of-second to within a
small number of nanoseconds. The limiting factor in your PC's clock
accuracy is likely to be the speed at which it can respond to the
change in the PPS signal (which typically requires taking an
interrupt).

A good timekeeping package should be able to compare an averaged PPS
timing (over a period of some minutes) with your system's inherent
clock drift, and figure out how to jiggle the internal clock so that
the drift averages down to zero. You should end up with time accuracy
good to within a few milliseconds.

On Linux, you can do this by running "gpsd" to monitor the GPS, and
having it feed timing information into the NTP daemon. In effect,
your GPS then serves as a new time source to the local NTP timing
pool... it's very accurate in the long term but somewhat prone to
short-term jitter. You can, if you wish, configure the ntp daemon to
use both the local GPS time source, and one or more network time
servers... this will give you redundency in both directions.

And *stay away* from
the stratum one servers like NIST; they have better things to do than
keep your computer's clock on time.

Correct. Use "pool.ntp.org", or one of the regional subdomains
thereof (e.g. "us.pool.ntp.org"). These domains point to a list
of well-connected, relatively-high-stratrum servers which have
volunteered to serve as public NTP resources.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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