[time-nuts] Time stamping with a PICPET

["Björn"]

Chris,

> So basically what you are proposing is an NTP reference clock that queries
> a known good external clock at semi-random intervals.  The query method is
> to send a pulse then read the time from the external clock.
>
> GPS is a "push" device.  It just sends data forever.  What you are wanting
> is a "pull" device, one that will tell you the absolute time of a pulse.
> It would not be hard to build.  Get a 32 bit counter that is driven by a
> 10MHz GPSDO.  then a pulse will latch the counter.   You'd need a very
> fast logic family if you plan to count nanoseconds.

This is already available even in some small mass market receivers. See
the uBlox Lea-6T and other uBlox receivers.

    "Time mark of external event inputs"

This has also been available in high quality L1 receivers and L1/L2
receivers used for airborne photogrammetry.

Read the text on page 40 and onwards of the Ashtech G12 manual

    http://goo.gl/Oc1htQ

The same feature is also available in all(?) the bus interface T/F cards
from Bancomm/Datum/Symmetricom/Truetime/Spectracom/KSI/Odetics etc.

   "Event Time Capture. An Event Time Capture feature provides a means of
latching time for an external event input."

from

    http://www.symmetricom.com/products/bus-level-timing/legacy-pci/bc635PCI-U-IRIG/


> The query would not be once per second.  NTP would use its normal method
> to
> determine the interval, usually it is much longer than one second.
>
> I bet there must already be an NTP ref clock that is based on query.  that
> could be a starting place.

See the Palisade refclock driver

     http://www.eecis.udel.edu/~mills/ntp/html/drivers/driver29.html

kind regards,

    Björn