[ntp:questions] ATOM falseticker with flag3 enabled

A C agcarver+ntp at acarver.net
Sun Apr 1 04:16:19 UTC 2012

On 3/31/2012 20:19, David Lord wrote:
> A C wrote:
>>> I'm not sure which value you are referring to. From the
>>> "ntpq -p" billboard over a day, I see values of jitter
>>> of the GPS as low as 0.002
>> Yes, it's that jitter however there's a minimum computed value below
>> which it never goes (varies per system). On my system it used to be
>> computed at 0.061 (and all the configured clocks would report that as
>> an initial jitter until some data came in). On the same system with
>> 4.2.7 the value is now computed to be 0.122.
>> In any case apparently according to David Hart the code has indeed
>> changed so the computations are different.
> Even after warm restarts I don't concern myself with the
> level of jitter until ntpd has had time to stabilise. After
> an update to ntpd or kernel, and without a pps source, it
> can be a day or more until a stable value for drift has
> been established.

It's not that I'm concerned about the jitter of the sources.  I just 
didn't understand why my copy was calculating a minimum system jitter 
that was twice the previous value.

> Has using 4.2.7 solved the problem with the type 20 and 22
> drivers both being marked as falsetickers?

Not that I've seen.  I'm still getting a falseticker on ATOM but I 
haven't figured out why just yet.  It might simply be my system and not 
a general bug.

> Were you able to determine a reasonable fudge time value
> for the type 20 driver by using noselect for the type 20
> driver and having several good internet sources?

I picked a reasonable number and it seems to hold but my GPS wanders by 
upwards of +/- 50ms so I didn't play with the fudge time much beyond a 
basic round number.  I got close enough and left it alone.

More information about the questions mailing list