[ntp:questions] dcf77 receiver makes ntp unstable? (drift and offset get jumpy)

Brad Knowles brad at stop.mail-abuse.org
Mon Feb 7 14:55:03 UTC 2005

At 3:27 PM +0100 2005-02-07, Folkert van Heusden wrote:

>  But in that case it is a problem over here, isn't it? My system does use a
>  dcf receiver across a rs232 line.

	Which is why I mentioned that point.

>>  -- the sort of thing that you'd want to use the
>>  PPSKit mods for, if you were using kernel 2.4.
>  Unfortunately my dcf receiver doesn't emit a pps signal.

	Hmm.  Looking at the output from "ntpq -p" on your machine, I see 
that your system has declared the local refclock to be insane.  If 
the system had declared it to be the syspeer, but it had higher 
jitter due to the lack of PPS, then I would imagine that that could 
affect the overall jitter on your system.

	However, with your local refclock being considered insane, the 
only thing I can think of is that you might still be losing 
interrupts as your system tries to service the serial port, and this 
could result in your drift and offset wandering around like that.

	Or maybe you're clock-hopping?  Going back and forth between 
being considered insane and the syspeer for this local refclock and 
other upstream Stratum 1 servers, could also explain what's happening 
to your drift and offset.

	I dunno.  Are you seeing anything in the logs related to ntpd?

Brad Knowles, <brad at stop.mail-abuse.org>

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."

     -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
     Assembly to the Governor, November 11, 1755

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