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

John Hasler jhasler at newsguy.com
Fri Jul 16 12:53:38 UTC 2010

Sebastian writes:
> 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 RTC.  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.

So your FPGA is decoding the DCF-77 format and extracting the PPS from
it?  And the controlling MCU is doing likewise?  And you want the MCU to
tell the FPGA to switch from decoding the DCF-77 signal to using a PPS
from the MCU the instant the DCF-77 signal goes down?

Why not just have the FPGA use the PPS from the MCU all the time?  And
why involve Ntpd?  You don't seem to want or need it's capabilities.
John Hasler 
jhasler at newsguy.com
Dancing Horse Hill
Elmwood, WI USA

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