On 06/25/12 18:43, Damien Dusha wrote:
Dear NTP list,
I would like to use the shared memory driver to push time from a GPS
receiver into NTP (Note 1) - host OS is Linux, using NTP 4.2.6p5.
According to documentation at
http://www.eecis.udel.edu/~mills/ntp/html/drivers/driver28.html, I
need to populate the following structure in shared memory:
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; /* external clock */
int clockTimeStampUSec; /* external clock */
time_t receiveTimeStampSec; /* internal clock, when external
value was received */
int receiveTimeStampUSec; /* internal clock, when external
value was received */
int leap;
int precision;
int nsamples;
int valid;
int dummy[10];
};
Whilst "mode" is clearly documented in the designated HTML page, the
remaining fields are not and it's not obvious as to how they should be
populated.
For poking around ntpd and gpsd, I have made guesses that:
* The timestamps are unix timestamps in UTC
* "leap" is an enumeration 0 - 3, though I am not entirely sure of
its meaning, (3 is unknown leap seconds applied?)
* "Precision" is 2^(precision) seconds estimated accuracy
* "count" and "valid" are populated according to the "mode" selected
But this is little more than a stab in the dark. Is there a better
place where these fields are documented that I have missed?
I think you have pretty much what you need. The leap values are just
what they are for the rest of NTP. Since the timestamps are in
microseconds, you probably want to set precision to -20. You get to
choose what mode you want to use. The nsamples field is set by ntpd.
Seems pretty clear.
--
blu
Always code as if the guy who ends up maintaining your code will be a
violent psychopath who knows where you live. - Martin Golding
-----------------------------------------------------------------------|
Brian Utterback - Solaris RPE, Oracle Corporation.
Ph:603-262-3916, Em:[email protected]
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