Mailinglist Archive: opensuse (1420 mails)

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Re: [opensuse] openSUSE + gpsd + PPS + NTP
On 2014-01-14 09:51, Roger Oberholtzer wrote:

Our main question is how the system acts if, at boot, there is no GPS data.
the time left alone? When the time does arrive, how quickly will the system
clock reflect the time? For example, it may turn out that the PC clock and
GPS time differ by some hours. Does NTP always do a gradual time shift? Can
that be disabled? These systems are booted a couple times a day.

When the NTP daemon is already running, it always compensates very
slowly. It simply speeds up or slows down the system clock till it gets
in sync with the reference, and this can take hours. It is done
intentionally slowly so as not to disrupt (much) Linux processes that
rely on clock timings.

When the difference between the computer time and the found reference is
too large, ntp simply bails out.

However, when you start the ntp service, the service startup script does
first a clock setup to the reference, and this can jump years if needed
in a milisecond. Once the computer clock is adjusted, the daemon is
started and takes over syncing the computer system clock and the
reference (maybe again adjusting the clock, but slowly).

You probably will need "something" to tell the operator if the system
clock is in absolute sync with GPS or not, and then... well, you have to
decide if your software does something or if the operator does something
or whatever :-)

Cheers / Saludos,

Carlos E. R.
(from 12.3 x86_64 "Dartmouth" at Telcontar)

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