Well, I got a WWV signal (also verified by John Miles) and it looks like the
Thunderbolt post dates the 1PPS pulse. The start of the TSIP primary timing
message follows the 1PPS pulse by around 20 msec.
The timing message ends 40-45 msec after the 1PPS pulse. Interesting that is
it is not a fixed or random delay. It seems to be quantized to 40, 45, or
occasionally 50 msec. The delay does not change randomly, but seems to
settle on a particular value for extended periods. Heather now assumes it is
45 msec. Not sure how much of the message jitter is from the Tbolt or Windoze.
Here is a run that John Miles did that compares Heather Standard Time to NIST.
I think you need to add the ping delay (or ping/2 ?) to the reported NIST
offset to get the true offset...
Anyway it looks like Heather can keep your Windoze clock fairly accurate...
probably within a Windoze timer tick (or two). One could probably do better
by hooking the 1PPS signal to a modem control interrupt (Carrier Detect?) but
that opens up a fresh can 'o nematodes.
C:\dev\gpib\tools>ping time-a.timefreq.bldrdoc.gov Pinging
time-a.timefreq.bldrdoc.gov [132.163.4.101] with 32 bytes of data: Reply from
132.163.4.101: bytes=32 time=63ms TTL=52
Reply from 132.163.4.101: bytes=32 time=65ms TTL=52
Reply from 132.163.4.101: bytes=32 time=65ms TTL=52
Reply from 132.163.4.101: bytes=32 time=62ms TTL=52 Ping statistics for
132.163.4.101:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 62ms, Maximum = 65ms, Average = 63ms C:\dev\gpib\tools>daytime 4
Usage: daytime [/set] [tries] [delay] PC= Mon Mar 22 17:02:28 2010
55278.001725 55278 10-03-23 00:02:29 50 0 0 0.0 UTC(NIST) PC= -0.018 s
55278.001732 55278 10-03-23 00:02:30 50 0 0 341.9 UTC(NIST) PC= -0.051 s
55278.001739 55278 10-03-23 00:02:31 50 0 0 714.0 UTC(NIST) PC= -0.054 s
55278.001747 55278 10-03-23 00:02:31 50 0 0 86.1 UTC(NIST) PC= -0.041 s
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