[ntp:questions] Time synchronization

Rob nomail at example.com
Fri Feb 6 19:59:25 UTC 2009


David Mills <mills at udel.edu> wrote:
> Third, the data reported is not from ntpd, but another daemon called 
> gpsd. Apparently it doesn'tt like the PPS signal. I don't know what 
> grooming algorithm it uses, but both the kernel and atom driver use a 
> trimmed-mean median filter, which is a rather heave dose of signal 
> processing that probably would not be the first inspiration of folks who 
> have not studied the detailed statistics.

gpsd does not perform any filtering at all.  it puts the timestamp
data from NMEA and PPS into shared memory and lets ntpd do all the
filtering via the shm driver.




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