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

Matuschka, Sebastian Sebastian.Matuschka at gcd-solutions.de
Tue Jul 13 07:32:56 UTC 2010

> > 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
> > signal is received for a few seconds.
> > How can I achieve this?
> A question: why do you want that?

Thank you for the answers.
The reason i want to switch very soon to another source when DCF77
signal is lost, is that I have to tell a FPGA when it should use the
DCF77 signal and when to use an alternative source. The FPGA doesn't
decodes the time but it uses the DCF77 signal to increment its internal
The MCU on which the ntpd runs has to decide whether the FPGA should use
the DCF77 or a "once per second pulse" from the MCU.
I guess I'm abusing ntpd a bit for something it isn't meant to be for.
But with a small hack somewhere in the ntpd sources it should be
possible to work as I need it.
Can you point me in the right direction? I've read through some
sourcefiles but I don't think I will find the correct location on my
Best Regards

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