[ntp:questions] ntpd: time reset problem

David Lord snews at lordynet.org
Thu Sep 17 09:35:52 UTC 2009

David J Taylor wrote:
> "David Lord" <> wrote in message news:7hd884F2t62hbU1 at mid.individual.net...
> []
>> That's good enough for me. The usb connection rules out
>> PPS mode and seems to limit to +/-10ms.
>> cheers
>> David
> Why rule out PPS?  I tried a GPS/PPS signal over USB and found a jitter 
> of about 45 microseconds:
>  http://www.satsignal.eu/ntp/NTP-on-Windows-serial-port.html#usb
> I suspect that's far better than a radio-clock would require.  If your 
> USB hardware/software allows, I would certainly try PPS.


I have tried it with radioclkd2 and that locks up with
100% load on both systems tried from NetBSD or Linux on
eeepc whenever timepps is selected via serial to usb
and correct source is selected, ie if source doesn't
have signal active, receiver off, it does nothing but
with receiver powered up it locks up and if logging
output there are many MBs of errors in a few seconds
before lock up.

NetBSD doesn't support TIOCMIOWAIT mode available on
Linux and using poll mode gets me +/- 10ms.

On Linux I can use wait mode which gives better than
+/- 2ms.

The NetBSD server has multiple serial ports anyway and in
that case timepps mode of radioclkd2 does work very well,
much better than GPS without pps, but I can't find the
table of comparative results just now.

What I've not tried so far over usb or direct to serial
port, is pps on DCD with type 22 driver and radioclkd2
using signal on a different pin CTS, DSR or possibly RNG.

There are a couple of problems with that, the pps signal
needs to be extracted from the demodulated carrier, and
cable I have wired up only has DCD.

I have a monostable setup to give a 950ms pulse before
it can be retriggered and other half of chip generates a
short pulse when 950ms pulse is triggered. I believe that
should give me a pps output from MSF but not yet given it
a try.


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