Not sure if I consider this as a spam but...

Zucca

I've spent way too much time configuring chrony (complex ntp program).
I added several ntp servers into my list, but only four pools, which are those in the default config.
From those pools chrony gets some random servers. I assume chrony is given the servers with least delay or based on location.

Anyways. I sometimes go and list the "sources" (servers) to see the stats:

pietinger · Posted: Sun Jan 14, 2024 7:03 pm Post subject:

As a paranoid person, I would never use a pool where I don't know which server I will actually be connected to. ;-)

My chrony is only allowed to connect to two servers with atom time in my country (secured by FW).

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NeddySeagoon · Posted: Sun Jan 14, 2024 7:53 pm Post subject:

I cheat, I have my own stratum 1 ntp server.
I use the gentoo pools as backup.

Hmm, it can only see two satellites :(
The garage roof must be wet.
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Zucca · Posted: Sun Jan 14, 2024 8:05 pm Post subject:

szatox · Advocate Joined: 27 Aug 2013 Posts: 3137

Zucca · Posted: Sun Jan 14, 2024 8:29 pm Post subject:

NeddySeagoon · Posted: Sun Jan 14, 2024 8:47 pm Post subject:

szatox,

PPS tells you the boundary between seconds, its just an IRQ.
Serial tells you which second, so you need both.

If you don't care about subsecond precision, serial alone will do what you want.
Jitter may be horrible as the NEMA sentence length varies.
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Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

pietinger · Posted: Sun Jan 14, 2024 8:58 pm Post subject:

szatox · Advocate Joined: 27 Aug 2013 Posts: 3137

Yeah, I know what PPS does, it's just that my GPS receiver doesn't provide that line, and the last time I tried it, I did not get the impression that ntpd would accept any input at all from a GPS receiver unless it provided PPS too. Hence my question about alternatives... Would be pretty cool if it was actually already supported and I just missed it though.
Or maybe it was gpsd that was the problem? It's been a while, I only vaguely remember it. Still, the fact remains that I came, I saw, I advanced in a different direction.

sMueggli · Guru Joined: 03 Sep 2022 Posts: 370

pa4wdh · l33t Joined: 16 Dec 2005 Posts: 812

Zucca · Posted: Mon Jan 15, 2024 8:48 pm Post subject:

Thanks. I'll keep that in mind. I have some PCs lying around which have DB9 serial. Some even have good old parallel port.
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szatox · Advocate Joined: 27 Aug 2013 Posts: 3137

Zucca · Posted: Mon Jan 15, 2024 9:43 pm Post subject:

Banana · Veteran Joined: 21 May 2004 Posts: 1392 Location: Germany

Not the latest but a nice display how it got slower: https://danluu.com/input-lag/
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pa4wdh · l33t Joined: 16 Dec 2005 Posts: 812

szatox · Advocate Joined: 27 Aug 2013 Posts: 3137

Sure PPS is better, I'm not arguing against that. What exactly are you going to do with those 1.998ms though?

I'd rather get whatever value I can out of a device I already have in front of me than get a new device which does the same thing marginally better. 1000 times 0 is still 0, I won't be able to tell a difference with pps or without.
Bonus points if said device happens to be a mobile phone with a GPS receiver soldered to the board and no exposed GPIO, so now I need 2 new devices just to put something on each end of discipline, instead of 1 I already have which would be good enough if I was able to make it actually do the thing it is already capable of doing.

pa4wdh · l33t Joined: 16 Dec 2005 Posts: 812

To me running your own ntp server is all about accuracy, because if it isn't for accuracy, why wouldn't i just use some timesource from the internet?
Part of the fun is to tune it and try to get to even higher accuracy. Having PPS helps, PPS connected to a serial port or GPIO helps even more, running ntpd with high priority helps, running the least amount of other processes helps. Ideally i'd want the GPIO interrupt and ntpd to be isolated and handled by the same CPU core with nothing else, but i can't do that with my Pi2B+ because all hardware interrupts seem to be fixed to cpu core 0.
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szatox · Advocate Joined: 27 Aug 2013 Posts: 3137

Well, if timekeeping is your hobby, that's a a valid point. Have you tried comparing your gps-pie to another atomic clock? I wonder how it fares.

pa4wdh · l33t Joined: 16 Dec 2005 Posts: 812

Yeah, i always had a fascination with time ... :-)

I've never compared it to any atomic clock, and i guess/assume the atomic clock will be better by a big margin. If i remember correctly the GPS signal should be capable of delivering 0,1us accuracy but my Pi simply can't keep up.
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The gentoo way of bringing peace to the world:
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Ralphred · Guru Joined: 31 Dec 2013 Posts: 501