Good evening!
On 1/10/2021 12:03 PM, ASSI wrote:
All modern OS that NTPsec runs on provide nanosecond resolution. The prcision
and accuracy of those measurements vary with the hardware, the rasPi in
particular is limited to something on the order of 150ns granularity as it
runs the GPIO off a 19.2MHz clock.
Thank you much for your reply - I wasn't aware that the RPi ran the GPIO off of
a 19.2 MHz clock, so this makes a lot of sense. :)
So, for a "normal" setup I'd trust maybe 10 microsecond figures, but you can
get it down into the 100 nanosecond range with some care.
Very good! Nice to know that the displayed figures are believable. :)
delay offset jitter
=======================
0.076 1.180 0.261
The jitter seems pretty high and the delay is oddly low. Has the NTP loop
actually converged already? If you use a rasPi with Gigabit Ethernet make
sure you switch off any link power management and set a fixed CPU frequency.
I'm not sure if the NTP loop has converged or not. This RPi that I'm using has
not had any power management or fixed CPU frequency adjustments - it has the
stock software load. However, now that it has been running for a while, ntpq
is now reporting:
pi@spy-pi:~ $ ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
*192.168.4.66 .PPS. 1 u 94 1024 377 0.097 0.320 0.081
+192.168.4.50 .PPS. 1 u 849 1024 377 0.374 0.371 0.072
+192.168.4.57 .PPS. 1 u 1071 1024 377 0.341 0.377 0.114
So perhaps now the NTP loop has converged? I'm not sure.
I should note:
192.168.4.66 is the Teensy 4.1 based GPS/NTP server.
192.168.4.50 is the RPi with standard NTP-based GPS/NTP server.
192.168.4.57 is the RPi with the NPT-Sec based GPS/NTP server.
Thanks much and 73,
ben, kd5byb
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