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

A C agcarver+ntp at acarver.net
Wed Aug 24 05:26:39 UTC 2011

On 8/23/2011 21:26, David Lord wrote:
> A C wrote:
>> On 8/23/2011 15:27, unruh wrote:
>>> On 2011-08-23, Uwe Klein<uwe at klein-habertwedt.de> wrote:
>>>> unruh wrote:
>>>>> But from his test, his system is labelling both edges.
>>>> so he has bounces on the line?
>>>> either that or rise/falltime is so low and noise so high
>>>> that receiver hysteris is not sufficient to supress multiple
>>>> HL/LH changes?
>>> No, his test shows that the line changes and then 100ms later it changes
>>> back and 900ms later it changes again (ie once per second it rises and
>>> falls.) Ie, it is behaving exactly as it should if it were detecting a
>>> pulse 100ms long.It is detecting both the rising and falling edge.
>> I just checked and the pulse is almost exactly 100 ms low going and
>> 900 ms high (within about 1 ms) so it's 90% duty cycle high most of
>> the time with a swing low. The signal itself is clean down to
>> microvolt levels. The total voltage swing is about 12 volts (which
>> would stand to reason since I'm feeding the TTL level PPS output of
>> the GPS board through one channel of a MAX232 level shifter).
>> Therefore the machine is receiving a nice, clean PPS signal on DCD
>> (DCD pin was also verified yet again and is correct by hardware
>> specifications).
> You seem to be saying that the rs232 signal is low going,
> ie low for 100ms then high for 900ms?
> Previously I had the impression the pulse was high going
> and you were using 'flag2 0'.
> Ntpd requires the prefer peer to be within mindist before
> even considering the PPS and then the system clock has to
> be within a millisec of the PPS. Using one of your other
> sources as prefer peer and having NMEA disabled might give
> you a better chance of getting the pps working without
> having to bother about the time2 value.

At first I couldn't remember which way the pulse went.  But having 
measured it now the voltage goes low (which would be an assert under 
RS232) for 100ms and then returns to high voltage for 900ms.

Either way, flag2 made no difference (I did try it both ways) but I'll 
try it again using another network clock as the preferred peer and see 
what happens.

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