[ntp:questions] ntpd on embedded risc
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
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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