[ntp:questions] Re: PPS working or not? FreeBSD 5.4

John Pettitt jpp at cloudview.com
Mon Jan 30 08:51:37 UTC 2006

David J Taylor wrote:

> Per, thanks for that.  I think I understand what you are saying (although 
> I may not next week!):
> - you need to recompile the kernel if you want the PPS signal to 
> discipline the local clock directly
> - there is an alternative programming interface, the PPSAPI, which FreeBSD 
> supports, but this API is not used by the NEMA driver.  (Why not?)
> - you may be able to use the PPSAPI if you install the ATOM driver as well 
> as the NMEA driver.
> I wonder which the preferred approach is, and which would give the better 
> results?
> I'm trying to put together a small Web page on this, so I may quote your 
> words (if that's OK).
> Thanks,
> David 

Both approaches work - I find the PPS_SYNC approach works better on machines that are subject to
thermal drift - letting ntpd do it is too slow and my machines spend all day chasing the thermal
drift and never get close to the right time.  You can turn kernel PPS on and off with a flag so once
you have build a kernel with PPS_SYNC you can use it either way.

The ntptime command will show you a bunch of info on the current PPS status.


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