LKM Timemark Driver

Gary E. Miller gem at
Tue Aug 28 18:41:11 UTC 2018

Yo Achim!

On Tue, 28 Aug 2018 19:45:32 +0200
Achim Gratz via devel <devel at> wrote:

> > The time from clock_gettime() is very coarse.  Not up to our needs.
> > On a Raspberry Pi 3B+ running 64 bit kernel the granularity is only
> > 52 ns.  
> That doesn't really matter, it is still about three orders of
> magnitude improvement over what we get today for the error that
> matters.

Ah no.  Lukas says 200 ns.  I can easily get under 1,000 ns.  Sometimes
down to 400 ns with care.  That is 2x, maybe 5x, certinaly not three
orders of magnitude.  You'll have 3 orders of magnitude when you
get to 1 ns jitter.  No consumer GPS can do that.

> We don't need to determine any interrupt latency when there's no such
> latency involved because we don't go through an interrupt for doing
> the measurement.

No need to keep beating that dead horse.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at  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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