[ntp:questions] Fwd: Re: NetBSD GPS/PPS using 4.2.6p3

Thomas Laus lausts at acm.org
Tue Aug 23 13:02:54 UTC 2011


On 2011-08-22, A C <agcarver+ntp at acarver.net> wrote:
> Yes but ntpd still doesn't see the PPS signal on DCD with or without 
> flag3.  So I'm lost on how to solve this problem.  I know the PPS signal 
> is there on the wire, I know DCD is being asserted and cleared.  I know 
> the test code can see it but for some reason I just can't make ntpd see it.
>
Does your PPS signal stay at logic 0 for most of the time and go to
logic 1 for a short time?  Does the PPS signal stay at logic 1 level
for most of the time and then go to logic 0 for a short time?  You
will require either an analog voltmeter or oscilloscope to read this
data.  Some GPS receivers generate a very short pulse and require
intervening hardware to stretch the pulse width to something the PC
can read reliably.  The capture / assert configuration options does
not select reading the leading or trailing edge of a PPS pulse, NTP
only reads timestamps to the on the leading edge and you may require
an inverter to swap polatity for NetBSD to read and sync to your PPS
pulse.

Tom

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