[ntp:questions] Re: May ntp be off by a second in case of GPSsource?

Eric ejensen at spamcop.net
Fri Dec 30 17:09:02 UTC 2005

On Fri, 30 Dec 2005 14:22:12 GMT, KomkaP at prolan.hu (Komka Péter) wrote
for the entire planet to see:

>Thomas Laus wrote:
>> "At the tone, the time will be xx:xx"
>> The GPS receiver sends the timestamp message for the next PPS pulse and
>> the NTP software uses the exact time of the pulse to synchronize the
>> local clock.
>So, can it be stated that NTP (strictly) requires (and will require) such a 
>GPS receiver?
>(Operating such that the stamp tells, in advance, what will be the time at the 
>following PPS-signal.)

NTP doesn't require a local reference clock at all.  And if you want
one, NTP supports quite a few drivers for different models.  

I use one that interfaces the other way, where the NTP (on the PC)
raises an RS232 signal line (RTS, I think) and the reference clock
saves the time at that instant and then sends that time, a variable
number of  milliseconds later, to the PC/NTP via the serial
connection.  No PPS in use, but it does sync pretty well.

- Eric

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