[time-nuts] Re: Poor's man NTP

[David Taylor]

On 16/12/2021 23:37, giuseppe at marullo.it wrote:
> Hi,
> 
> just wondering if a PI4 could be a suitable NTP server for a small lab (and
> maybe with some other NTP servers for my company, about 2000 clients).
> 
> Main use is for correct timestamp on logs/computer time sync.
> 
> I setup the NTP using Adafruit Ultimate GPS shield(with battery), and the
> GPS/GLONASS Antenna(cheap one, not a timing antenna). Antenna is on a roof
> window with a small metal base, outside.
> 
> What is the accuracy I could expect from it?

You can see the offsets reported by a number of Raspberry Pi NTP servers here:

   https://www.satsignal.eu/mrtg/performance_ntp.php

As a very rough guide I would expect a PPS-based RPi to be within 100 us 
easily, and perhaps considerably better (~10 us) in a constant temperature 
environment, and with no other load.  I don't know about load capacity as I've 
not tested that, but here it's serving perhaps 50 devices.  With classic NTP 
which is what I use there will be a period before the offset becomes near-zero 
so 24 x 7 is the way to operate.

Although there are some devices on that page with LAN, 2.4 GHz or 5 GHz 
connections, for beat accuracy you must use the PPS signal from the GPS as you 
know.  The "o" tally code suggests that's OK.

I suggest using the "pool" directive rather than multiple pool servers:

   https://www.satsignal.eu/ntp/setup.html#pool

Cheers,
David
-- 
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