VERSION 1.0 -- JOHN BATTLES -- DECEMBER 2004

NTP PRE-FLIGHT CHECK PROCEDURE.


1) Make sure gps is attached and sending good data to COM4 /dev/ttyS3

2) Type ntpq at command prompt as root

3) type the peers command at the ntpq> prompt.

ntpq> peers

     remote           refid      st t when poll reach   delay   offset  
jitter
==============================================================================
*GPS_NMEA(0)     .GPS.            0 l    8   64   37    0.000  -754.53  49.693
 infohost.NMT.ED 132.163.4.102    2 u    7  256   17    1.127  -62.079   5.837
 LOCAL(0)        LOCAL(0)        10 l    3   64   37    0.000    0.000   0.001


You should get something similar to the above.  The thing to check is that 
        1) the GPS_NMEA(0) line is present.  
        2) The stratum (st) is set to 0
        3) The jitter column is less than 4000 ms.  4000ms is the max. 
jitter. the deaomon will handle before ignoring the clock driver.
values of 50-200 are in the normal range.


The next command to check is 
ntpq>clockvar

status=0000 clk_okay, last_clk_okay,
device="NMEA GPS Clock",
timecode="$GPGGA,224346,3403.9667,N,10654.4480,W,1,07,1.7,1453.7,M,-23.7,M,,*4F",
poll=3, noreply=0, badformat=0, baddata=0, fudgetime1=0.000, stratum=0,
refid=GPS, flags=0
 
Here you should see the last line from the gps under "timecode=$GPGGA.."
You can check the status fields for any erros in helping to debug.  
noreply=  gives a count of how many times the ntpd tried to poll the gps 
and didn't get a response.  

Notes:
- The 'date' command can be used to see what the current time is. 

-Use 'date -s hh:mm'  to set the time as close as possible to UTC.  This will 
speed up the time lock on.

About ntp.conf in /etc

Should have a config line that looks like:

server 127.127.20.0 mode 2 burst prefer

       127.127.20.0 - sets ntpd to use NMEA serial gps /dev/gps0
		    gps0 should be a link to /dev/ttyS? wher ? is 0-3

        mode 2 - Use NMEA GGA string for time.
	burst - when checking time use 2s burst intervals.  Time is set faster.
	prefer - Use as statum 0 (highest) level clock driver.