[time-nuts] Leap second glitches on NTP using Z3801A

M. Warner Losh imp at bsdimp.com
Mon Nov 17 05:01:41 UTC 2008


In message: <fbddc0730811162028o44c0f8fcl185ac139794f5b53 at mail.gmail.com>
            "Eric Garner" <garnere at gmail.com> writes:
: Sorry for not forming my question better. I guess what I wanted to
: know is that given that the first leap second was in 1972 and that the
: first GPS satellite was launched in 1993. why was it decided to not
: incorporate leap seconds into how GPS "tells" time, but still alerts
: you to the fact that they are coming up? Or why was the decision made
: to have UTC-GPS different than UTC. My understanding is that they
: "tick" simultaneously but "tell" different times.(sorry for the
: overuse of quotes)  Is there some navigational reason? Is it actually
: intentional?

Leap seconds suck.  There's no reason to have them unless you need
time to sync up with the way that the earth is pointing.  GPS doesn't
need to synchronize to the earth's directions to solve for location,
so it saves a ton of hassles by just counting seconds since an
arbitrary epoch.  Since UTC is important, GPS's almanac gives the
conversion from GPS to UTC.

Warner


: -eric
: 
: On Sun, Nov 16, 2008 at 8:08 PM, Brooke Clarke <brooke at pacific.net> wrote:
: > Hi Eric:
: >
: > So that you can figure out UTC.  But there's no DST bit on any of the
: > satellites so for that you need a local time broadcast.
: >
: >
: > Have Fun,
: >
: > Brooke Clarke
: > http://www.prc68.com
: >
: > Eric Garner wrote:
: >> Ascending from Lurk Mode, I have a (possibly stupid) question: according to
: >>
: >> http://tycho.usno.navy.mil/leapsec.html
: >>
: >> and Tony Jones's book "The Story of Atomic Time" GPS time does not
: >> account for leap seconds, So why does it alert you to them?
: >>
: >> -eric
: >>
: >> On Sun, Nov 16, 2008 at 7:21 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
: >>> Is anybody running ntpd with their Z3801A?
: >>>
: >>> If so, please check your log files and tell me if you see a bogus leap second
: >>> at the end of the past several months.  I've seen them for Aug, Sep, and Oct.
: >>>  I think they are coming from my Z3801A, but it might be something else.
: >>>
: >>> The GPS satellites are now announcing a leap second that will happen at the
: >>> end of the year.   The refclock driver passes that to ntpd and ntpd passes it
: >>> to the kernel and magic happens.
: >>>
: >>> I think the refclock-ntpd interface assumes the leap second will happen at
: >>> the end of the current month.  NIST only announces leap seconds a month ahead
: >>> on WWVB and ACTS.
: >>>
: >>> The Oncore refclock driver has a filter to wait until the current month to
: >>> pass the info to ntpd.  I'm working on something similar for the HP driver.
: >>>
: >>> --
: >>> These are my opinions, not necessarily my employer's.  I hate spam.
: >>>
: >>>
: >>>
: >>>
: >>> _______________________________________________
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: >>>
: >>
: >>
: >>
: >
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: 
: 
: 
: -- 
: --Eric
: _________________________________________
: Eric Garner
: 
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