[ntp:questions] Change reference clock soon after DCF-signal is lost

Rob nomail at example.com
Thu Jul 8 15:06:10 UTC 2010

Matuschka, Sebastian <Sebastian.Matuschka at gcd-solutions.de> wrote:
> Hi,
> i'm new here and have a question I couldn't answer by myself by
> searching the internet and reading the documentation for hours.
> I have a DCF77 Clock connected to the UART. The line in the ntp.conf
> looks like this:
> server mode 5 prefer
> Receiving the time works, but when I disconnect the DCF77-Receiver from
> the UART, ntpq -p says that ntpd still synchronizes with it for minutes
> (about 4), until it changes to another clock.
> I want that the ntpd changes the synchronization source as soon as no
> signal is received for a few seconds.
> How can I achieve this?

A question: why do you want that?

Because of the structure of the DCF77 format, it is basically only
known that the synchronization is lost at the end of every minute.
At that time the bits of the transmitted time, that are spread out
over the entire minute, are evaluated to see if there are parity
errors or other errors that indicate loss of sync.

So maybe it should lose sync after a minute, but not much sooner
than that.

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