[ntp:questions] problem with ntpd refclock and pps via parallel port

unruh unruh at wormhole.physics.ubc.ca
Mon Feb 1 17:52:49 UTC 2010

On 2010-02-01, David Lord <snews at lordynet.org> wrote:
> unruh wrote:
>> On 2010-01-31, David Lord <snews at lordynet.org> wrote:
>>> problem with ntpd refclock and  pps via parallel port
>>> Hi
>>> So does pps really need a refclock and/or does pps via
>>> parallel work ok or not on NetBSD-5?
>> Yes. Otherwise it has no idea what the seconds is. Ie, all pps does is
>> deliver a pulse at the exact second boundary, but that says nothing
>> about which second that is the boundary of. You need some other source
>> to give you the seconds.
> Sorry, I missed mention of the local ntp peers.
> There were three local servers to give time to second, one being
> a pool server with radioclock that I was attempting to distribute
> pps from via parallel port. Docs I have indicate a server can be
> used to get "second" in place of refclock,

Yes, it certainly can. However you should make sure that your system is
within a half second of the correct time before starting the PPS.
Otherwise the PPS will just take the current seconds, and lock you onto
a time which is out by seconds.

> I'm now thinking that might still be the case and parallel port
> implementation on NetBSD isn't correct. I've not yet had time
> to figure out where I'm currently getting my pps from, DCD on
> serial, or NACK on lpt0.
> I can try again on desktop but now I have present config working
> will give that a week to get some reasonable stats.
> cheers
> David

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