[time-nuts] Cheap jitter measurements
Gary E. Miller
gem at rellim.com
Tue Apr 10 18:58:51 EDT 2018
Yo Hal!
On Tue, 10 Apr 2018 15:41:41 -0700
Hal Murray <hmurray at megapathdsl.net> wrote:
> > Yeah, but the granularity is much worse.
>
> Do you have code that demonstrates that? (or tell me how and I'll
> try it)
Look in gpsd git head. In the contrib directory here is a program:
clock_test.c
It tests the time to do two back to back clock_gettime(). Output
looks like this:
# ./clock_test
samples 101, delay 10000000 ns
min 67 ns, max 302 ns, mean 176 ns, median 197 ns, StdDev 52 ns
You run it a few times and you will see the granularity in the
measurements is 10's of ns, or more, depending on your CPU.
Probably better discussed on the gpsd-users@ or NTPsec devel@ mailing
list. 67 ns not exactly time-nuts precision.
RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
gem at rellim.com Tel:+1 541 382 8588
Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin
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