|
From: | David Taylor |
Subject: | Re: Web page updates following recent discussions |
Date: | Thu, 21 Jan 2021 10:44:02 +0000 |
User-agent: | Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 |
On 20/01/2021 17:48, Gary E. Miller wrote:
Yo David! On Wed, 20 Jan 2021 11:35:52 +0000 David Taylor <gm8arv@yahoo.co.uk> wrote:On 19/01/2021 19:31, Gary E. Miller wrote:There has been lots of earlier discussion on this with ntpviz providing read data. I suggest you setup ntpviz and collect real data. RGDS GARYThanks for that pointer, Gary. I've been collecting NTP data for some years now, and I'm basically happy with this.Care to sahre your data?- to disable the OS from setting the RTC - I gather there's an 11-minute time controlling thisThat is certainly not the way Uputronics says to do it. That breaks the RTC disciplining. The preferred method is to let it free run and store the drift. See "man hwclock".- to have the RTC cause an interrupt (say every minute) and record the PPS-disciplined system time when that happens.I don't see how the Uputrnics can do that.There's no suggestion of using the RTC to control system time other than at initial power-up. It's more an exercise to measure the RTC itself.If you just want ntpd to measure, not use, the RTC, then set it "noselect". Otherewise ntpd will eventually use it4. RGDS GARY
My simple NTP data is on my Web site, and the MRTG/Perl scripts I use. For example:
https://www.satsignal.eu/mrtg/performance_ntp.php https://www.satsignal.eu/ntp/NTPandMRTG.htmlYes, I am trying to measure the RTC without disciplining. As interrupts are not possible I will try polling, recording the time when the second digit (or value) changes. This with just the i2c connection to the RTC - no OS or server connection. Reading the bytes directly. Something to experiment with.
The first problem with NTP reading the RTC may be that once NTP knows about it it may try and discipline it, preventing a long-term measurement, and the second that the RTC can only be read in seconds, so even without the disciplining you might be waiting for many weeks for the RTC to be a second off!
On making the RPi alone as accurate as possible, some RPI 4B show a ppm offset of -9 -11, and -19, so far worse than the RTC.
Cheers, David -- SatSignal Software - Quality software for you Web: https://www.satsignal.eu Email: david-taylor@blueyonder.co.uk Twitter: @gm8arv
[Prev in Thread] | Current Thread | [Next in Thread] |