[ntp:questions] NTP.conf using Dave Hart code.

BK bkreiger at sigmatechcorp.com
Tue Feb 9 20:19:09 UTC 2010


First I installed NTP4.2.4p8
Then I updated the binaries with your updates labeled 4.2.7p8
Then I installed the serial PPS driver 20091228

Although for NTP purposes, you would like only one output string, I
have to output two NMEA strings because there is another device
looking at the serial stream also.  I am outputting GGA and RMC
messages.  According to the GPS manufacturer (I am using a Garmin
GPS15H) the PPS signal is applied just before outputting the NMEA
sentences that would be for that time period.  I have the PPS signal
set to 80ms width.  One oddity about my configuration is that the NTP
server will not be up 24x7.  The machine will be booted, and I would
like the ntpd to discipline the local clock to a reasonable (+-10ms)
accuracy within 10 minutes. I have another machine that I will then
synchronize to the computer with the GPS.

Looking at the documentation it appears you can specify which NMEA
string to use so perhaps this is better

#the below line is just to remind me how cruddy the base clock might
fudge stratum 5

#tell NMEA reflclock to use RMC messages
server minpoll 4 mode 1
# tell NMEA refclock to use PPS
fudge refid gps stratum 1 flag1 1

It really doesn't matter to me if I install the serialPPS driver or
not.  From your discussion it appears using the serialPPS driver is
more accurate than the NMEA driver? Does that make it a better choice
or is that just making it more confusing?

And I really appreciate your help, I have been trying to research this
as much as possible on the internet, but I am having a little
difficulty because it appears that there are a fair number of
differences between the Linux usage of PPS and the windows PPS, etc.

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