Mailinglist Archive: opensuse (1420 mails)

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Re: [opensuse] openSUSE + gpsd + PPS + NTP
  • From: Roger Oberholtzer <roger@xxxxxx>
  • Date: Wed, 15 Jan 2014 08:24:19 +0100
  • Message-id: <1519476.S7VD7asBfE@acme>
On Tuesday, January 14, 2014 09:47:42 PM Carlos E. R. wrote:

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.

Leaving those Linux processes that rely on accurate time at all times to fend
for themselves... This is a I understand things to be.

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).

Sounds good. But in the case of a GPS providing the times, it assumes that the
GPS has satellite fix when it runs. In a moving vehicle, this is not always the

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 :-)

This is something I am trying to design. I need to know (1) did the GPS have
sat fix when ntp started and (2) has the time completed being adjusted as
needed. #2 must, I would imagine, be ascertainable from NTP logs. #1 is most
likely something we will need to implement.

Yours sincerely,

Roger Oberholtzer

Ramböll RST / Systems

Office: Int +46 10-615 60 20
Mobile: Int +46 70-815 1696

Ramböll Sverige AB
Krukmakargatan 21
P.O. Box 17009
SE-104 62 Stockholm, Sweden
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