diff options
| -rw-r--r-- | host/docs/gpsdo_x3x0.dox | 57 |
1 files changed, 49 insertions, 8 deletions
diff --git a/host/docs/gpsdo_x3x0.dox b/host/docs/gpsdo_x3x0.dox index 24997d50b..9577b930d 100644 --- a/host/docs/gpsdo_x3x0.dox +++ b/host/docs/gpsdo_x3x0.dox @@ -46,12 +46,22 @@ pins.</b> \section gpsdox_using Using the GPSDO in Your Application -By default, if a GPSDO is detected at startup, the USRP will be -configured to use it as a frequency and time reference. The internal -VITA timestamp will be initialized to the GPS time, and the internal -oscillator will be phase-locked to the 10MHz GPSDO reference. If the -GPSDO is not locked to satellites, the VITA time will not be -initialized. +If a GPSDO is detected at startup, the USRP will have `gpsdo` clock and time +source options. + +Select these by using UHD's + +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp} + usrp->set_clock_source("gpsdo"); + usrp->set_time_source("gpsdo"); +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +That will lock the reference clock to the disciplined 10MHz oscillator, and +will make the USRP listen for time signal pulses coming from the GPSDO. + +However, you will still need to explicitly set the device time on such a PPS +edge, using the `set_time_next_pps` or `set_time_unknown_pps` +calls. GPS data is obtained through the **mboard_sensors** interface. To retrieve the current GPS time, use the **gps_time** sensor: @@ -65,12 +75,43 @@ January 1, 1970. This value is readily converted into human-readable format using the **time.h** library in C, **boost::posix_time** in C++, etc. +\subsection Setting Device Time to GPS time + +If you want to set the device time to GPS time, the following procedure makes +sure you don't encounter timing problems while doing so: + +1. Wait for GPS lock, and then set the time source to GPSDO, +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp} + while(! (usrp->get_mboard_sensor("gps_locked",0).to_bool()) ) { + boost::this_thread::sleep(boost::posix_time::seconds(2)); + } + usrp->set_time_source("gpsdo"); +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +2. poll on `usrp->get_time_last_pps()` until a change is seen, and then sleep 200ms to allow new time data coming from the GPSDO to propagate through the system, +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp} + uhd::time_spec_t last = usrp->get_time_last_pps(); + uhd::time_spec_t next = usrp->get_time_last_pps(); + while(next == last) { + boost::this_thread::sleep(boost::posix_time::seconds(0.05)); + last = next; + next = usrp->get_time_last_pps(); + } + boost::this_thread::sleep(boost::posix_time::seconds(0.2)); +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +3. use +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp} +usrp->set_time_next_pps(uhd::time_spec_t(usrp->get_mboard_sensor("gps_time").to_int()+1)); +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +to set the time, +4. poll on `usrp->get_time_last_pps()` until a change is seen and sleep 200ms (allow NMEA string to propagate), +5. Verify that `usrp->get_time_last_pps()` and `usrp->get_mboard_sensor("gps_time")` return the same time. + +\subsection Further GPS sensors + Other information can be fetched as well. You can query the lock status with the **gps_locked** sensor, as well as obtain raw NMEA sentences using the **gps_gprmc**, and **gps_gpgga** sensors. Location information can be parsed out of the **gps_gpgga** sensor by using **gpsd** or another NMEA parser. - - */ // vim:ft=doxygen: |