On 2015-02-21, Rob <[email protected]> wrote: > William Unruh <[email protected]> wrote: >> On 2015-02-19, Rob <[email protected]> wrote: >>> Miroslav Lichvar <[email protected]> wrote: >>>> On Thu, Feb 19, 2015 at 12:48:46PM +0000, Rob wrote: >>>>> I am still finding out what sensor is best to use, we do have a room >>>>> temperature sensor that has .1C resolution and is readable via snmp, >>>>> and there are the usual sensors for board- and inlet air temperature. >>>>> (and of course CPU temperature) >>>>> >>>>> It does not matter if it is only a course indication, the room temperature >>>>> varies over a -10 .. 50C range (don't ask...) and a 1C resolution is not >>>>> bad relative to that. >>>> >>>> In my tests using a sensor with 1C resolution it was barely useful >>>> with NTP sources and 1024s polling interval. If the sensitivity is >>>> around 0.1 ppm per degree, 1C resolution means the compensation >>>> jumping the frequency in 0.1ppm steps. That's a lot, especially if you >>>> compare it to the tracking skew with a refclock. >>> >>> Ok but of course we are using PPS and a 16 second polling interval. >>> (or maybe the PPS refclock polls even faster although it displays 4 as >>> the poll interval indicator) >> >> The shm refclock will get one pulse per second, and then average the >> offsets over a 16 sec period after getting rid of the outliers. > > I am not using the SHM refclock in those systems.
What are you using? Are you on ntpd or chrony? As I recall ntpd in its pps refclock also collect say 16 outputs of PPS, finds the median, thros away the 40% greatest outliers and reports the resultant median to ntpd as the current offset. That is the same kind of filter chrony uses in its shm driver. _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
