[time-nuts] TSIP, SCIP time sync

[Hal Murray]

holrum at hotmail.com said:
> 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.

I'm running NTP on Linux.  I'm seeing about 10 ms of jitter.  That's after 
all of NTP's filtering.

My stuff changed when I turn on the low-latency flag for that serial port.  I 
didn't say "got better".  The graph looks cleaner.  I think it removed some 
of the high frequency jitter.  The remainder reminds me of the hanging 
bridges - very hard to filter out.


> 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.

That's the way to go if you want good timing.  Beware, there is a big 
rat-hole in making computers keep good time, and it's got "time-nuts" written 
all over it.

DCD is the common pin for that purpose.  Some OSes support other pins.

Pin 1 (DCD) on the TBolt isn't connected to anything.  I added a jumper over 
to the PPS connector which is conveniently nearby.  More news when the 
self-survey finishes.  (Which may take a long time since my antenna setup is 
poor.)

Pins 6 (DSR) and 9  (RI) have traces that are visible.  One goes to an empty 
resistor.  The other goes to chip marked "232".  I assume it's a level 
converter.  If so, it's an output pin.  All the documentation I've found says 
"Not used".  Maybe I mistraced someting.




-- 
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