On 1/27/20 4:17 PM, Rick Moen wrote:
Quoting Dr. Nikolaus Klepp (dr.kl...@gmx.at):
Just for your amusement: systemd breaks linuxcnc on RPi4 - who's not
into machining will most likely not see the fun part of it, but anyway
:)
https://www.youtube.com/watch?v=RDKaFJmB254
Nik --
Thank you for the link. I think it should be of interest for people
wanting to observe an inquisitive mind doing good diagnosis work,
whether they are interested in linuxcnc or not, e.g., right around the
11:35 minute mark (out of 14:43) he arrives at the important conclusion,
through logical testing, that systemd's timesyncd implements an
un-gentle jerk-forward-or-back of time all at once -- as opposed to the
gradual adjustment any of the real NTP daemons would do -- and that such
rough time discontinuities are problematic for real-time operations.
(It's distinctive that the entire RPi series lacks by default any RTC
circuitry, so it's particularly vulnerable to such software problems.)
Starting around 13:00, he tests his hypothesis by switching to ntpd, and
indeed the observed symptom immediately goes away.
I have an OpenSUSE system that exhibits a similar thing... Periodically xymon
tells me the time server isn't acceptable, and the shuttle motherboard HAS an
RTC. It's not running ntpd.
I also have a PI with a GPS clock board and a special build of ntpd to enable support for it. From time to time, even though checks of the GPS clock show it's running correctly,
IT does the same thing too.
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