[ntp:questions] NTPD Refclock Driver documentation

Thomas Koehler mailbox.koehler at gmail.com
Thu Mar 24 10:28:35 UTC 2016


my question refers to the documentation of Refclock Driver (Type 22).

The following is included in this documentation:

"The driver includes extensive signal sanity checks and grooming
algorithms. A range gate and frequency discriminator reject noise and
signals with incorrect frequency. A multiple-stage median filter rejects
jitter due to hardware interrupt and operating system latencies. A
trimmed-mean algorithm determines the best time samples. With typical
workstations and processing loads, the incidental jitter can be reduced
to a few microseconds."

According to my review of the source, this does not apply to the type 22
driver only. As I understand, the mentioned filters are part of
ntpd_refclock.c and so apply to all refclock drivers.

Am I right and this description should be moved to the refclock
documentation site? A few thesis papers I read cite this fact only as
part of the type 22 driver.

Thanks for answer,


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