[time-nuts] LTE-Lite module
phk at phk.freebsd.dk
Mon Oct 20 15:41:42 EDT 2014
In message <60CC0E0EEEE34928B664249EAC88407F at pc52>, "Tom Van Baak" writes:
>This is the best news I've heard in a long time; an overhaul of NTP!
>Instead of tweaking GPSDO algorithms or tuning parameters and
>having to wait days to see if it works or not, the idea was to
>"replay" pre-recorded 1PPS data and pre-recorded oscillator data
>into the PLL. This means one can test any new design change in a
>GPSDO in a matter of seconds instead of days.
>So the question is -- could you do the same for NTP?
Well, first of all it's not days any longer. My proto-PLL wrangles
the clock phase in a matter of seconds and frequency in a few
minutes. Some of the (really) old NTP assumptions and metrics no
longer hold, revisiting them opens up a lot of parameter space.
Second, I'm already doing such simulations, and the ability to
do that is part of the design basis of what I'm doing.
I spent a month of my NTP-time trying to resurrect the "SIM" code in
ntpd, in order to get some kind of reproducible test-bench going and
in the end I concluded that 100k lines of code is not the way forward.
My current plan is to release a brand new client-only NTP daemon
with a decent PLL and high attack resistance before X-mas and then
work from there to one or two other programs: NTP-slave server (ie:
stratum 2..14) and a NTP-master/stratum 1 server.
All along the way, the intent is to try to pull PTP into this also,
since there is no material (ie: only protocol) difference between
a NTP and PTP timekeeping program, and the user shouldn't need to
notice the difference.
More as it happens.
The "mini-blog" entries I've started will happen every so often
when there is some progress to report or interesting data to
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
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