[LinuxPPS] Processing PPS through NTPs shared-memory reference clock

[Loretta Goldberg]

I have both a pulse-per-second signal and a time-of-day message coming from my gps.  The pulse-per-second will be designated as the "prefer" instance of the shared-memory reference clock.  The time stamp for the pulse-per-second will not be passed to NTP until NTP has "locked on" to the time stamp coming from the time-of-day message.
 
I have a GPS for which a reference clock does not exist, so I have to write an external app, and pass the time to NTP via the shared-memory reference clock.
 
My restrictions are RHEL as is, no adding the PPS support to the kernel.
ntp4.2.4p4 as provided by Redhat (no changes allowed).  I know that the shared-memory reference clock was modified  for (ntp-4.2.5p138) to collect data each second, rather than once per polling interval.  
 
What would be the impact of this modification on how accurately I can estimate the current time from a given GPS?  
 
If my system requirements specify that I have to use a version of NTP that predates this modification, can I attain the same accuracy from my GPS?
 
Is the limitation that it will take me longer to synchronize to my GPS?  Or does the increased polling interval prevent me from attaining the same degree of accuracy in my estimation of the current time?
 


      
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://ml.enneenne.com/pipermail/linuxpps/attachments/20100223/89a74859/attachment.htm