[ntp:questions] What should the poll be for the shared memory driver (type 28)?
snews at lordynet.org
Mon Jun 17 16:12:25 UTC 2013
David Taylor wrote:
> What should the poll be for the shared memory driver (type 28)? This
> Web page:
> suggests that the driver internally has a poll interval of 1 second,
> another document I've seen suggests setting:
> server 127.127.28.1 minpoll 1 prefer
> and yet in the ntpq -p billboard the poll is shown as 8 seconds.
> Loopstats are reported at 8 second intervals, and the poll interval is
> shown as 3 (i.e. 8 seconds).
> I'm confused! What should be the correct setting in the ntp.conf file?
I've used type-28 + radioclkd2 for many years with MSF and for a
while with DCF. I've never set minpoll/maxpoll but it has always
defaulted to 6, ie 64 sec. DCF has a phase shift second marker
but is too distant for that to useful. When DCF reception was
good the timekeeping was better than from msf (+/- 0.1 ms vs 1ms).
As you mentioned above, type 28 refclock pages indicate the driver
is polled by ntp at 1 second intervals (as from ntpd-4.2.5p138).
> BTW: this comes about from Folkert van Heusden who is using a user-mode
> program to make NTP on a Raspberry Pi more precise, i.e. providing PPS
> support without having to modify the kernel. See:
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