[ntp:questions] ntpd on embedded risc

David Woolley david at ex.djwhome.demon.co.uk.invalid
Thu Feb 19 07:56:57 UTC 2009

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.

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