[ntp:questions] Using Trimble TSIP under Linux

David Taylor david-taylor at blueyonder.co.uk.invalid
Mon Oct 29 09:11:06 UTC 2012

On 29/10/2012 08:38, Rob wrote:
> David Taylor <david-taylor at blueyonder.co.uk.invalid> wrote:
>> - use sudo ppstest /dev/pps0 and see assert pulses coming in
>>     (the clear field is always 0 though, perhaps the 150
>>      microsecond pulse is too narrow?)
> That is a problem!
> Now I remember...
> I tried different GPS receivers when writing the code for the PPS
> support in gpsd, and there was a receiver for which it would not
> work because the pulse is too narrow for the technique used in gpsd.
> It was the Trimble, I remember now.
> You need to add a circuit to stretch the narrow pulse into a 100ms
> pulse.  The exact duration is not important.  Just arrange for a
> monostable multivibrator that gets triggered by the rising edge
> of the pulse and extends the pulse by R/C time.  Make sure the pulse
> is shorter than 500ms or the autodetection logic will focus on the
> wrong edge of the pulse.

Thanks, Rob.  For the moment I have decided to use the pps-gpio code 
which has been written for the Raspberry Pi, rather than the gpsd route. 
  This is producing valid data when running the ppstest (although the 
entries of "0" in the clear values worry me slightly), and from the NTP 
log I believe that the version I have may not have ATOM support.  I've 
recompiled NTP, and am thinking about installing it....

I really would prefer not to have to add extra hardware at this point.
Web: http://www.satsignal.eu

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