[ntp:questions] Use of the shmTime-struct

meder at whoi.edu meder at whoi.edu
Wed Jun 30 21:20:58 UTC 2010


I am looking at the shared memory structure and code used by NTP and was
wondering if I could get some guidance on these values.  The big question is
how NTP uses the clockTime vs the receiveTime.

Trying to also understand the unit (unitptr) concept and which shared memory
location(s) I should use if I have just a single time source.

I also do not see a big difference between mode 0 and 1 especially given the
valid field, but maybe someone could shed light on those.  I gather precision
is not used?

struct shmTime {
	int    mode; /* 0 - if valid set
		      *       use values,
		      *       clear valid
		      * 1 - if valid set
		      *       if count before and after read of values is equal,
		      *         use values
		      *       clear valid
		      */
	int    count;
	time_t clockTimeStampSec;
	int    clockTimeStampUSec;
	time_t receiveTimeStampSec;
	int    receiveTimeStampUSec;
	int    leap;
	int    precision;
	int    nsamples;
	int    valid;
	int    dummy[10];
};

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