[time-nuts] TEC party file format?

Hal Murray hmurray at megapathdsl.net
Tue Jun 28 22:39:20 UTC 2011

> How does NTP handle the cases where an accurate 1PPS is available but the
> time itself isn't? This would be the case for most cesium or OCXO
> references, or maybe even some GPS 1PPS references.

You need to get the rough time from some other source, say the network or  
from GPS via the serial port.

I thought the PPS driver would ignore input pulses that are not close enough 
(say 125ms or 250ms) but I can't find it in a quick scan of the code so maybe 
I'm imagining things.

Note that a Cesium or OCXO will drift.   Even if the drift isn't a problem, 
you have to get their PPS lined up with the second ticks.  GPSDOs are good.  
:)  [You can also measure the offset.  NTP can work with that.]

> Or, use a software divider: let the user program that's reading the 60 bytes/
> second pulse DTR once every 60 bytes, tie this to NTP's DCD pin and -- the
> PC is generating its own 1PPS. 

There is a shared memory driver that lets you do something like that without 
any hardware.  Look at the gpsd sources if you want to see how to feed it.

For things like this, ntpd has a "noselect" option for a server or refclock.  
It collects all the data but doesn't use it, just puts it in log files.

These are my opinions, not necessarily my employer's.  I hate spam.

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