[ntp:questions] ntpd on embedded risc

Hans Jørgen Jakobsen hjj at wheel.dk
Sat Feb 21 21:10:56 UTC 2009


On Thu, 19 Feb 2009 13:14:01 -0800 (PST), cnm3332 at gmail.com wrote:
> On Feb 19, 1:56 am, David Woolley
><da... at ex.djwhome.demon.co.uk.invalid> wrote:
>> Hans Jørgen Jakobsen wrote:
>> > precision=-7 is not that spectacular.
>> > Are there other options for clocks on the board?
>>
>> Exactly, although the convergence time requirements are also unrealistic
>> for ntpd.
>>
>> precision -7 tends to suggest the hardware is using a 10ms clock with no
>> interpolation, which means that times read by the application, and in
>> ntpd offsets, have a built in 10ms peak to peak error term.
>>
>> Once converged to a network source, one would expect up to an order of
>> magnitude better setting for the time than indicated by the offset, but
>> you will still only be able to read it to 10ms.  I'm not sure that there
>> will be enough noise in the SHM PPS readings to dither them
>> successfully, so there is some risk that it will hop between two 10ms steps.
>
> Hm, so perhaps hardware is not ideal for NTP server then.  I think I
> will
> start looking at other embedded systems then, maybe sticking with
> x86 like via eden or something.  Is there anyway I can know accuracy
> of clock?  People have recommendations on what small systems
> I should try?

Or you should look at soekris.com. I have no personal exp.
PHK and other has written something about these boards.
http://phk.freebsd.dk/soekris/pps/
Warning: You are entering an area that will take much of your time :)
/hjj




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