[time-nuts] Noob question, NTP stratum 1.

[Peter Membrey]

Hi guys,

A little late to the party but hopefully someone finds this useful.

As the Raspberry Pi family of IoT devices are so popular and have been used in a host of different research projects to gather data (much of it including timing information), we were curious as to how stable the Raspberry Pi was and whether it was suitable for such work. To understand this better we characterised the main counter on the board (the STC) for all three generations of Pi available at the time. We presented the results at IMC2016 in "Time to measure the Pi" which is available here:

http://crin.eng.uts.edu.au/~darryl/Publications/Pi-hat_current.pdf

We also looked at how well it performed with NTP and also characterised the uBlox M8Q as a potential time source.

The Pi's (especially the latest generation at the time, the Pi 3) did surprisingly well and behaved similarly to what we previously observed in a "big box" machine.

In terms of its suitability as an NTP server, again it held up really well. That said until the Pi 4 (which I am still waiting to get my hands on), the network interface on the Pi goes through an internal USB hub and suffers from significant jitter. I've not sat down and studied it in depth, but initial tests showed occasional spikes well into the millisecond range.

Lastly although the Pi's are impressive given their price point and they can perform well for many use cases, there is a reason why Microsemi sells their solutions for 100x the price. At home or in the office, a Pi3 with a uBlox M8Q (with a good view of the sky) is likely to give you better results than using a random server from the Internet's NTP Pool, but I wouldn't want to bet on it for keeping critical infrastructure in sync (it's not going to do well in holdover situations for example).

Kind Regards,

Peter Membrey



----- Original Message -----
From: "Luiz Paulo Damaceno" <luizpauloeletrico42 at gmail.com>
To: "wildylion" <wildylion at protonmail.com>, "Discussion of precise time and frequency measurement" <time-nuts at lists.febo.com>
Sent: Tuesday, 23 July, 2019 01:31:34
Subject: Re: [time-nuts] Noob question, NTP stratum 1.

Dear colleagues, i've made some tests and wrote an article about Raspberry
Pi as a timeserver. I think we can trust on it and this board can keep a
good time from GNSS PPS. I'm open to suggestions. I hope this can help in
the decision making process. The link: rpi_article
<https://www.researchgate.net/publication/334179026_Credit_card_size_computer_Stratum_1_NTP_Server>

Also, in our tests as you can see in the article, for general purposes the
RPI has a good dealing with high loads. The difference is we've removed the
crystal oscillator and put a signal from a synthesizer, you can keep the
crystal and trust on pps signal too. I'm using a server at home with a
cheap module NEO-6M and also one with SAM-M8Q. For comparsions effect i've
put the NEO-6M to compare the ntp time of the rpi that this receiver is
connected to with the server from the article: you can see in the
thingspeak: thingspeak_channel
<https://thingspeak.com/channels/691405/>

If you want the source code for the 1 PPS generation thats it:
1pps_generation_src_code
<https://github.com/LuizPauloDamaceno/rpi_pps_out/blob/master/ppsout.c>

Best regards,

Luiz

Em seg, 22 de jul de 2019 às 11:05, wildylion via time-nuts <
time-nuts at lists.febo.com> escreveu:

> Hello there,
>
> I wanted to ask for advice regarding NTP
>
> Situation 1:
> What I currently have is a uBlox M8N GPS puck I'm planning to use with the
> Raspberry PI. Seems like it should work almost out of the box with some
> kernel tuning, but I have a question about short term stability in the
> event of GPS loss - how well will the board hold over if it's lost GPS for,
> say, 24 hours?
>
> Situation 2:
> Also, there's a need for more dependable NTP time sources for our
> colocated spaces.
>
> What we have is about 100 servers, some of them running DBMS that wouldn't
> like clock drift at all. After a recent incident involving NTP I've got an
> idea to install GPSDO time servers in each datacenter and slave them to
> stratum2's that will be actually distributing time to clients.
>
> All the certified GNSS disciplined clocks are really expensive (way more
> than the management would approve), so what I'm planning to do is possibly
> getting a couple LeoNTP units and using them as the root time sources,
> would this be a good plan? Of course, all the NTP infrastructure will be
> monitored, and possibly we'll use Stratum 2 servers which would be slaved
> to GPSDO S1's AND the public NTP pool for sanity checks.
>
> Maybe BG7TBL's units instead of LeoNTP?
> Is that a good idea?
>
> Sent with [ProtonMail](https://protonmail.com) Secure Email.
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.
>
_______________________________________________
time-nuts mailing list -- time-nuts at lists.febo.com
To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.