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

A C agcarver+ntp at acarver.net
Tue Aug 23 14:25:58 UTC 2011

On 8/23/2011 06:02, Thomas Laus wrote:
> 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.

The duty cycle is about 10% (100ms on 900ms off).  I'll try tossing in 
the pulse stretcher and/or inverter just after the GPS receiver and see 
what happens.

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