[time-nuts] NTP Servers - RPi, NTP-Sec, Teensy 4.1, and one on the way from eBay

[ASSI]

Am Sonntag, 10. Januar 2021, 17:30:52 CET schrieb Ben Hall:
> While on the NTP-Sec server, on the output of ntpq, there are at least four:
> 
> delay   offset  jitter
> ======================
>   0.0000   0.0740   0.0027
> 85.4951  -1.7276  11.7616
> 40.9579  -1.9249  13.8848
> 25.7753  -0.5499  16.9417

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.

> Is this just trickery or is that real precision?  I don't know.

Here's the statistics from the NTP loop data of my NTPsec boxes for the last 
seven days:

tb1      PLL/FLL: bias = +1.284e-10s, mabs = 1.362e-07s (de-biased)
tb2      PLL/FLL: bias = +5.827e-10s, mabs = 2.510e-07s (de-biased)
rpi2     PLL/FLL: bias = -6.607e-11s, mabs = 2.507e-07s (de-biased)
rpi3     PLL/FLL: bias = -2.640e-09s, mabs = 1.665e-07s (de-biased)
rpi4     PLL/FLL: bias = -1.397e-09s, mabs = 3.081e-07s (de-biased)
rpi5     PLL/FLL: bias = -1.058e-09s, mabs = 2.743e-07s (de-biased)

These are all self-ovenized so they do run close to the measurement 
resolution.  One day I'll get around to try polling instead of interrupts to 
get rid of some of the noise and/or up the frequency on the GPIO, the hardware 
would allow 250MHz there…

These three are non-ovenized and have at least 10x worse performance:

rpi1     PLL/FLL: bias = -1.246e-07s, mabs = 1.552e-05s (de-biased)
gertrud  PLL/FLL: bias = -6.350e-07s, mabs = 6.341e-06s (de-biased)
otto     PLL/FLL: bias = -1.541e-07s, mabs = 1.456e-05s (de-biased)

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.

> While the Win10 box has yet to reach the Teensy 4.1-based NTP server,
> the RPi has no issues, likes what it sees, and uses it for time-sync
> without problem:
> 
> 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.


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

Factory and User Sound Singles for Waldorf Blofeld:
http://Synth.Stromeko.net/Downloads.html#WaldorfSounds