Gary E. Miller gem at rellim.com
Thu Sep 15 19:37:56 UTC 2016

Yo All!

I have some solid results on minpoll=maxpoll=2.  That gives a poll time
of 4 seconds.  This results set after about 43 hours of run time.  Eric
delegated me the task to fix for minnpoll=maxpoll=0.  On my list to fix
early next week.

First, the bbad news.  On a Raspberry Pi 3B, with Uputronics
hat, minpoll=maxpoll=2 (4s) results are a bit worse than than
minpoll=maxpoll=1 (2s).

At poll=4s:
      Local Clock Freq Offset: 90% 1.1ppm, Jitter 90% 0.08 us
      Local Stability 90%: 2.9 ppt
      PPS Offset  90% 2.2us, Jitter 90% 0.20 us

At poll=2s:
      Local Clock Freq Offset: 90% 1.1ppm, Jitter 90% 0.43 us
      Local Stability 90%: 2.3 ppt
      PPS Offset  90% 1.6us, Jitter 90% 0.34 us

At poll=64s:
      Local Clock Freq Offset: 90% 1.4ppm, Jitter 90% 3.3 us
      Local Stability 90%: 2.2 ppt
      PPS Offset  90% 68us, Jitter 90% 9.7 us

Poll=2s is still the bast for this hardware, but there is a little
tradeoff between offset and jitter.  Since NTP is about time, not
frequency, we go with the best time.

Now the good news.  On a quad XEON, with an MR-350P serial GPS:

At poll=4s:
    Local Clock Freq Offset: 90% 332ppb, Jitter 90% 20.9 us
    Local Stability 90%: 15,6 ppt
    PPS Offset  90% 40.6us, Jitter 90% 29.7 us

At poll=2s
    Local Clock Freq Offset: 90% 495ppb, Jitter 90% 16.9 us
    Local Stability 90%: 27.7 ppt
    PPS Offset  90% 39.0us, Jitter 90% 26.7 us

At poll=64s
    Local Clock Freq Offset: 90% 570ppb, Jitter 90% 10.2 us
    Local Stability 90%: 1.2 ppt
    PPS Offset  90% 34.2us, Jitter 90% 16.3 us

For this hardware poll=64s is stil the bast, and both low poll times are
much worse.

Not much to see in the graphs, so I skipped them.  Next time (poll=8s)
I'll put the numbers in chart form.

So, the answer to the best poll?  It depends, but poll=4s does not seem
optimal for my two cases.  So far poll=2s for RasPi+HAT, and poll=64s
for Xeon+Serial GPS.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588
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