[time-nuts] Re: Clock display on Linux systems?

[Adam Space]

Cool set-up :) Where are all of these clocks in the ntpq picture though?
I'm surprised that stratum 1 devices have such large offsets from each
other... A solid PPS set-up should easily give sub 1ms accuracy, but it
looks like these all disagree by a few, if not dozens of, ms. I assume this
is due to asymmetric network paths in NTP? Even so, I would've expected the
offsets to be lower. And what's up with the 80ms offset from time-c-wwv?

On Tue, Dec 7, 2021 at 8:59 AM John Sloan <jsloan at diag.com> wrote:

> I have four home-built clocks, each using a Raspberry Pi, all with
> slightly different designs, all running gpsd and ntpd (so all are NTP
> servers on my home network). Three are GPS disciplined; one is WWVB
> disciplined. Two of the GPS clocks use the modem-control lines on a serial
> port for the 1PPS signal, one uses the simulated modem-control signals on a
> USB-connected GPS dongle. One of the GPS clocks has a cesium chip-scale
> atomic clock - specifically, a Jackson Labs Technologies dev board with a
> Microsemi CSAC - for holdover (there’s no kill like overkill).
>
> All four clocks use an Adafruit “Pi Plate” LCD board with a two-line
> display to display the date and time.
>
> https://www.adafruit.com/product/1115
>
> The display format could have been anything I chose, but I implemented one
> that looks like this (using a 24-hour time so no AM/PM).
>
> Tue 2021-Dec-07
>  06:33:49 MST
>
> They all run the same trivial Python script that I wrote to read the
> system clock (which is disciplined to NTP, and hence to GPS or WWVB time)
> and drive the display. The script runs five times a second. Efficiency is
> not really an issue since this is running on a quad-core processor. An
> entire core could be dedicated to just updating the display. I leave that
> to the Linux scheduler. This approach combines the accuracy of
> GPS-disciplined time with support for time zones and Daylight Saving Time
> adjustments in the system clock.
>
> The time on the LCD is as accurate as I need it to be, since it’s just a
> human-read display. The NTP time provided by each clock is at least
> competitive with getting the time from NTP servers across the internet. I
> have another Raspberry Pi that uses ntpq to query all of my clocks, along
> with two commercial NTP servers on my network, plus two external servers,
> and compares them. Based on its own measurements, it typically chooses the
> atomic clock as the best reference.
>
> There is undoubtedly a lot of room for improvement in all of this,
> especially in my WWVB clock.
>
> Here is a link of all of my blog articles on clock- and time-related stuff.
>
> https://coverclock.blogspot.com/search/label/Horology
>
> Some of those articles will include links to my GitHub repositories for
> those projects.
>
> Here is an album of photographs of all of my NTP servers, both home-brew
> and commercial.
>
> https://flic.kr/s/aHsmgrizkL
>
> :John
>
> --
> J. L. Sloan             Digital Aggregates Corporation
> +1.303.489.5178         3440 Youngfield Street
> mailto:jsloan at diag.com  #209
> http://www.diag.com     Wheat Ridge CO 80033 USA
>
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