[ntp:questions] Problem troubleshooting gps/pps on freebsd 8.1
pst at telia.com
Thu Dec 16 15:19:34 UTC 2010
> I have successfully done that with FreeBSD V8.0, and following the
> instructions "To the letter" it works fine, all on an old Gateway small
> format desktop PC. The GPS (Garmin GPS16LVS) is powered by the
> reduntant mouse port too.
Hi Dave B.
The instruction didn't work 100% as when I installed 8.1 as it
installed another ntpd but an older one in another directory which
took me a while to catch because the version numbers didn't match.
Also my serial ports are named /dev/cuau0 and /dev/cuau1.
> You do have to configure the GPS RX to only spit out 1 posibly 2
> sentences (I went for GPRMC only.) What GPS RX are you using? Have
> you made sure with a 'scope for example, that the PPS signal is getting
> to the DCD pin, and is still enough volts, and wide enough to trigger it
> (he does suggest using a pulse of 200ms, but it's the leading edge
> that's used, not the entire pulse as such.)
> Some COM ports are a little reluctant to work relaibly with just a 0..5V
> signal, so it may need a buffer.
I have some electronics between the GPS and com port.
The scope looks like this:
(DCD on channel one and Rx on channel two)
I think it the voltage levels are OK.
I hope I use the correct flank on the DCD???
> One thing I did notice... Your ref clock server addresses 127.127.20.0
> Is that right? Should be 127.127.20.1 ???
> Assuming you got the symlink OK.
> link cuau0 gps1
> From that blog page... It does say:-
> It has the special IP address 127.127.20.x where x is the number of the
> GPS unit in /dev/gpsx.
> And illustrates that with:-
> server 127.127.20.1 mode 0 minpoll 4 maxpoll 4 prefer
> fudge 127.127.20.1 flag1 1 flag3 1 refid GPS
> Doing all that "*Exactly*" as he describes does work. I know, if I can
> make it work, the instructions must be OK! :-)
I used this instead:
link cuau0 gps0
I just used gps0 instead of gps1 since it seemed more logical. So that
why it's 127.127.20.0.
and I have "mode 16" because I use 9600 baud instead of 4800.
> Unless something is significantly different between FreeBSD V8.0 and 8.1
> And of course, you did recompile the Kernel, to support PPS? It has to
> be asked...
> Best Regards.
> Dave B.
Yes I did and I think the correct why to check if it works is to do:
[root@ ~]# ntpdc -c kern
And then look for this:
pps frequency: 25.103 ppm
pps stability: 1.537 ppm
pps jitter: 2.367e-06 s
calibration interval: 256 s
calibration cycles: 188
jitter exceeded: 24
stability exceeded: 0
calibration errors: 1
Thank for your help. It was the ntpd bug that was the primary problem
but there may still be other problems.
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