Look at the program shmpps which takes a pps signal, and populates the shm structure with the current offset .
On 2012-06-25, Damien Dusha <[email protected]> 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? > > Regards, > Damien. > > (Note 1: In this project, we are processing our own GPS solution and > time based on raw observables and are hence are not using NMEA or > other GPS protocol. PPS is supplied to us via a GPIO line and we are > using the ATOM driver to capture this via linuxpps). _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
