[time-nuts] PPS stats

[Hal Murray]

> NTP is using the PPS and my stats look good, but when I run
>     ntpq -c kerninfo
> The pps frequency, stability, and jitter are all zero.

>     dmesg | grep pps
> and
>      ppstest /dev/pps0
> both indicate the kernel pps support is working.

> Why isn't the kerninfo showing any info on the pps
> frequency, stability, and jitter?

There are 2 modes of PPS.  ntpq -p doesn't show the difference.

The normal mode is that ntpd processes each PPS pulse as a data point, just 
like a data point from a packet exchange with a NTP server.  (Not quite, there 
is an extra level of filtering, but close enough.)

The second mode is that the kernel does everything after ntpd turns on a bit.  
It's a kernel option.  Most distros don't include it - it conflicts with a 
scheduler option that saves power.  (aka you have to build your own kernel)  
Those slots get filled in when the kernel mode is running.

pll offset:            0
pll frequency:         -28.451
maximum error:         0.1055
estimated error:       3e-06
kernel status:         pll ppsfreq ppstime ppssignal nano
pll time constant:     6
precision:             1e-06
frequency tolerance:   500
pps frequency:         -28.451
pps stability:         0.012085
pps jitter:            0.007
calibration interval   256
calibration cycles:    1020
jitter exceeded:       13
stability exceeded:    0
calibration errors:    0


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