[ntp:questions] Using ntpd with custom clock

Rob nomail at example.com
Wed Oct 17 07:06:10 UTC 2012

Chuck Swiger <cswiger at mac.com> wrote:
> Hi--
> On Oct 16, 2012, at 2:49 PM, Felipe Blauth wrote:
>> 2012/10/16 Brian Utterback <brian.utterback at oracle.com>
>>> I think the original poster is asking to do something a little bit different than the usual. If I am reading it right, he is not asking how to get ntpd to read a custom clock as a source of time (which as noted is what a refclock is for). I think he is asking how to get ntpd to *set* a custom clock, treating it as it would the system clock, so as to sync the custom clock with the upstream NTP server time.
>> That's exactly what I want to do.
> OK.  You can either hook into ntpd's calls to get/settimeofday() and adjtime() as you initially suggested, or perhaps look into the SHM driver.  The latter is a generic interface that puts clock timestamps into shared memory; but you can read from SHM instead of writing, if you like-- would be easier if you have something like a GPS receiver and gpsd populating the SHM timestamps.

Funny that, after you initially seem to indicate that you have
understood the question, you still come up with the SHM driver
that is a REFERENCE CLOCK driver, not an ADJUSTMENT CLOCK driver.

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