Experimental Physics and
Industrial Control System

Bill Cruise <[email protected]> · Mon, 28 Jul 2003 15:06:39 -1000

Hi,

We are using a Datum TymServ(tm) 2100 Network Time Server with GPS
receiver option to provide our observatory with stratum one NTP.

In our IOC we have a Datum bc635VME Time and Frequency Processor.  This
is basically the same board which some other observatories use, only
most have GPS receiver options and ours gets the time from the 2100
by means of an IRIG connection.

We use the receiver to directly read time from the internal registers
via the VME buss, using direct calls.  This is done from inside a 
genSub record, and is the basic timing for our whole system.  We do not 
use any "real" drivers, and do not use the timing capabilities of the 
board.  We just read the time -- NOW.

The problem is that we have seen some timing glitches of 1 second and
10 seconds.  Last night there were four 1 second glitches.  The time
seems to be 1 second fast on one read, and then OK 0.050 seconds later.
This happens very rarely, and so far hasn't caused any real problems,
but the capability seems to be there.

Has anyone else encountered any such glitches in reading time from a
Datum GPS?  If so, have you developed a solution?  

Thanks for any help,

Bill

-- 

William L. Cruise                             [email protected]
Electronics System Supervisor                   FAX:    808 885-7288
Canada-France-Hawaii Telescope                  Voice:  808 885-3121
65-1238 Mamalahoa Highway         http://www.cfht.hawaii.edu/~cruise
Kamuela, HI   96743

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System