[time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

Chris Albertson albertson.chris at gmail.com
Wed Feb 15 13:17:17 EST 2017

On Tue, Feb 14, 2017 at 9:38 PM, MLewis <mlewis000 at rogers.com> wrote:

> That dual set model is new to me. Interesting to see its fall-back on
> failures. And the offline model.
> It's the poor-man's version of that model that I was aiming for (and one,
> not two sets of receiver-with-server):
> - A small box as "GPS receiver" with NTP, receiving the PPS from a GPS
> timing module.
> - That box as a source to an NTP Server that also looks at six internet pool
> sources (pools are the 'backup' if GPS/receiver-box fails).
> - My systems (two boxes) look to the NTP Server for their time reference.

Why set up a dedicated NTP server if you only have two computers that
will use it?    Your server will be accurate to a few microseconds but
your two computers will only by good to a few milliseconds because
ethernet is not nearly as good as PPS.

You could save some money and just run NTP on the two computers.   A
dedicated server does not get you much because you can't get GPS level
accuracy out of it to your other devices.     But this is a hobby and
setting it up is educational  And maybe you find other uses for the
server like maybe it can keep backups or store media files (videos) or
host a small web site   NTP is almost zero load on the CPU and the
best thing is the NTP accuracy is not effected by CPU load  SO you can
run other service without degrading the NTP server.  (All the time
critical stuff happens inside a tiny interrupt handler, not in user


Chris Albertson
Redondo Beach, California

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