[ntp:questions] site with lots of GPS's and accessories

Dennis Ferguson dennis.c.ferguson at gmail.com
Mon Mar 19 18:40:08 UTC 2012


On 19 Mar, 2012, at 13:58 , Alby VA wrote:
> Compared to this history of Atomic Clocks at NIST
> and this chart of accuracy, I'd say my NTP Server is
> in the 50yrs behind the curve.   lol  At least its portable.
> 
> History: http://www.nist.gov/pml/div688/grp40/nist-clocks.cfm
> Chart: http://upload.wikimedia.org/wikipedia/commons/9/9a/Clock_accurcy.jpg

You could do a lot better with hardware designed to timestamp
an edge.  The timestamp-in-an-interrupt-routine thing is a
hack that has never been outgrown.

This can be done with a peripheral interface designed for the
purpose, though this still leaves one with the problem of
transferring the peripheral clock's time to the computer (the
latter also seems to be the problem with IEEE 1588).  A
better way would be for Intel (or someone) to devote a CPU
pin to receiving signal transitions, along with the logic
to sample in hardware and deliver to software the contents
of the TSC at the time of an edge.  Then there'd be a
market for "timekeeping" motherboards, with that pin wired
to an appropriate receiver with an input connector and maybe
with a better quality crystal (with a synchronization
frequency input?) clocking the CPU complex.

Dennis Ferguson




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