[ntp:questions] Panic stop captured
agcarver+ntp at acarver.net
Sat Dec 15 20:15:06 UTC 2012
On 12/15/2012 02:43, Rob wrote:
> A C <agcarver+ntp at acarver.net> wrote:
>> Yes, the SHM is configured currently as the preferred peer and PPS is
>> the system peer usually. SHM is coming from gpsd and PPS is coming
>> directly from a serial port (separate from the one used by gpsd).
> I take it that you then use the first SHM provided by gpsd, the one
> that is calculated from the serial messages from the GPS receiver?
> It is quite usual that it wobbles by several hundred milliseconds
> on some receivers.
> The second SHM provided by gpsd is the PPS one, but in reality it is
> not independent of the first one, because of a limitation of SHM.
> It is not possible to convey PPS information via SHM, only absolute
> time information. So gpsd works around this by adding the current
> system time to the relative time provided by the PPS signal. As
> this is a circular definition, gpsd attempts to keep sanity by only
> putting valid time into the second segment when the system time is
> within some defined offset from the time received in the GPS serial
I only use the first SHM from gpsd (the time stamp). I do not use the
PPS SHM from gpsd. I use the ATOM refclock (22) and send the PPS signal
directly to ntpd via DCD on a second serial port. Yes, the first SHM
does wander around a bit but for the most part it stays on one side of
zero (on purpose, I have been tweaking the fudge time to try and keep it
More information about the questions