[ntp:questions] Re: PPS working or not? FreeBSD 5.4

John Pettitt jpp at cloudview.com
Sun Jan 29 19:00:33 UTC 2006

David J Taylor wrote:
> I just spent an interesting few hours setting up a FreeBSD 5.4 system from 
> scratch, and interfacing it to a Garmin GPS 18 LVC.  Well, there was a lot 
> of help in the Web, and it must be 10 or more years since I messed with 
> I'm getting what seem to be sensible results, but the jitter from the GPS 
> seems to be higher than some of the Internet servers (3ms versus 1ms), so 
> I'm wondering if the PPS signal on the DCD line is being used at all. 
> I've set flag3 = 1 in the fudge command.
> Any suggestions?  I'm really new to FreeBSD so I might have missed the 
> glaringly obvious!
> Thanks,
> David 

I have the same setup.

Jitter from a GPS18LVC should be on the order of 3-5 microseconds so I think your PPS is not working.

Things to check

1) PPS is wired to DCD
2) you are on a real serial port not a USB one
3) you made the sym link from /dev/pps0 to /dev/ttyd?
4) you have pps enabled in the GPS18 (download the garmin utils and turn off all the NMEA stuff you
don't need and make sure PPS is on)
5) you have "options PPS_SYNC" in your kernel config


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