[ntp:questions] ntpd PLL and clock overshoot

Bart Van Assche bart.vanassche at gmail.com
Sun Oct 8 09:55:54 UTC 2006


As known the PLL implemented in ntpd/ntp_loopfilter.c can overshoot. In 
the source code of ntpd 4.1.2 it is documented that this overshoot is 
less than 5 percent. Measurements I performed confirm this.

The PLL algorithms in ntpd 4.1.x and are 4.2.x different. The source 
code of ntpd 4.2.0 specifies that document UDel TR 97-4-3 documents the 
ntpd 4.2 PLL algorithm. Anyone any idea where I can find that document ? 
I could not find it via Google, and it's not in David Mills list of 
papers (http://www.cis.udel.edu/~mills/papers.html). I'm asking this 
because for ntpd 4.2.0 I measured an overshoot of about 100 percent. Can 
anyone confirm this ?




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