[ntp:questions] Re: Question to NTP developers

John Ackermann N8UR jra at febo.com
Thu Aug 24 13:23:03 UTC 2006

Hal Murray wrote:
>> There is only one GPS receiver and, of course, one PPS hardware signal.
>> How could the PPS signal be present on one server and absent on the
>> other in the same time ? This is my problem and I suspect 50% the
>> hardware on the motherboards and 50% the software (OS + NTP) !

What is the PPS pulse width coming out of the GPS?  A pulse that's too 
narrow won't be seen by the PC serial port hardware/software.

I have this issue with my Cs and Rb clocks.  One of the clock pulses 
about 15us wide, and will not work with my Linux system that uses the 
shared memory PPS refclock.  The same pulse works just fine with the 
ATOM driver on a FreeBSD box, on a slightly slower processor.  Another 
clock has a pulse that's a bit more than 20us wide, and that works fine 
on the Linux system.

While I think the Motorola receivers all have a wide pulse, some others 
are also down in the microsecond range.


More information about the questions mailing list