Re: [chrony-dev] adjusting frequency on the basis of temperature

[Bill Unruh <unruh@xxxxxxxxxxxxxx>]

On Tue, 7 Dec 2010, Michael Ashley wrote:

> Hi folks,
>
> Firstly, thanks for chrony, it is a very nice bit of software.
>
> I have some computers in Antarctica that are disconnected from the
> internet for days (potentially months) at a time. The temperature of
> these computers can range from -40C to +30C, and over this range there
> is a large (and highly predictable) variation in the clock frequency.

They really go from outside to inside (even that is surely not 30C) ?

> I wonder if chrony could be extended to allow for the frequency to be
> adjusted manually during periods where no reference clocks were
> available?

It already does allow you to feed in reference times by yourself. 
What you really want is for it to use measurements of the temp to estimate the
temp correction and to then adjust the clock for that change in temp. 
crystals have varying responses to temp. and it is not even clear how linear
it is over that range 70 c range.

> I was contemplating hacking into the refclock_sock.c code to add a new
> "sample" message which adjusted the frequency. Is this a sensible
> approach? Any pointers appreciated.

The better way would be link in a temp measurement (most motherboards have
temp probes on them) to do a regression on the temp as well as the time.
There have been a couple of attempts to do this with ntpd, but none that I know
of with chrony.


> Cheers,
> Michael
>
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William G. Unruh   |  Canadian Institute for|     Tel: +1(604)822-3273
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