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[gpsd-dev] PTP

From: Gary E. Miller
Subject: [gpsd-dev] PTP
Date: Fri, 20 Feb 2015 21:02:52 -0800

Yo All!

Harlan has been pushing me to look at PTP for a while and I finally did.

My initial interest was as another SHM based refclock, but this thing
is way cool.

On my local GigE network I have an NTP chimer with PPS that keeps
time with jitter on the order of 250 nSec.  Great.

Other NTP clients on the local network can only seem to sync to that
master to around 150 uS jitter.  Not great.

Linux PTP has the answer with their ptp4l daemon.  It uses special
low level protocols that do not require (but can use) special
ethernet adapters.  It syncs time between clients and then acts as
an SHM based refclock to chronyd or ntpd.

After installing ptp4l on my server and clients they now sync to
around 5 uSec jitter.  Wow.

So, before I forgot what I did, and before 3.12 ships, I added a new
section to the gpsd-time-service-howto.txt called:
         == Providing local NTP service ==

All the required steps are there in condensed form.  It may even make
sense to me in the morning.  It needs a lot of love and I'll try to add
it as I gain experience with it.  No doubt Eric and others will pick it
to pieces and thus make it a better document.  Please let the picking

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
        address@hidden  Tel:+1(541)382-8588

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