[LEAPSECS] real-time UT1 realisation
imp at bsdimp.com
Thu Sep 22 13:26:50 EDT 2011
On Sep 22, 2011, at 11:15 AM, Tom Van Baak wrote:
>> Eyeballing it says around a couple of milliseconds, which, unless
>> you have done things to your hardware, is lost in the NTP noise.
> That was my conclusion too. It's one thing to work with hardware
> at the micro- nano- or picosecond level. But the threshold with
> PC's, even PC's running NTP, is so relaxed that I figured almost
> any hack that uses a dut1 database would do the trick. The one
> I usually fetch is http://maia.usno.navy.mil/ser7/ser7.dat.
> Yesterday DUT1 was -0.30806, today is -0.30862, and tomorrow
> will be -0.30937. So it seems to me you could implement the
> google ntp server lie() function with essentially one line of code
> and it would be accurate to better than 1 ms. No interpolation,
> no filtering, no prediction; just a table lookup. Hard to beat that
> performance/simplicity ratio.
Yea, the hard part is keeping that table up to date, but I guess that's the job of a crontab entry not ntpd itself.
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