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diff --git a/host/docs/gpsdo.rst b/host/docs/gpsdo.rst new file mode 100644 index 000000000..dc03f6ae9 --- /dev/null +++ b/host/docs/gpsdo.rst @@ -0,0 +1,66 @@ +======================================================================== +UHD - Internal GPSDO Application Notes +======================================================================== + +.. contents:: Table of Contents + +This application note describes the use of integrated GPS-disciplined +oscillators with Ettus Research USRP devices. It pertains specifically +to the Jackson Labs Firefly-1A device unless noted otherwise. + +------------------------------------------------------------------------ +Specifications +------------------------------------------------------------------------ +Receiver type: 50 channel with WAAS, EGNOS, MSAS +10MHz ADEV: 1e-11 over >24h +1PPS RMS jitter: <50ns 1-sigma +Holdover: <11us over 3h +Phase noise: 1Hz: -80dBc/Hz, 10Hz: -110dBc/Hz, 100Hz: -135dBc/Hz, 1kHz: -145dBc/Hz, 10kHz: <-145dBc/Hz + +------------------------------------------------------------------------ +Installation +------------------------------------------------------------------------ +See the documentation for your device for specifics on installing the GPSDO. + +------------------------------------------------------------------------ +Configuring the USRP to use the GPSDO +------------------------------------------------------------------------ +This is necessary if you require absolute GPS time in your application, +or need to communicate with the GPSDO to obtain location, satellite info, etc. +If you only require 10MHz and PPS signals for reference or MIMO use, +(see the Synchronization application note), it is not necessary to perform +this step. + +To configure the USRP to communicate with the GPSDO, use the +usrp_burn_mb_eeprom utility: + +:: + $ cd <install-path>/share/uhd/utils + $ ./usrp_burn_mb_eeprom --key=gpsdo --val=internal + +This will configure the driver to communicate with the GPSDO on startup. + +------------------------------------------------------------------------ +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. + +GPS data is obtained through the mboard_sensors interface. To retrieve +the current GPS time, use the "gps_time" sensor: + +:: +usrp->get_mboard_sensor("gps_time"); + +The returned value will be the current epoch time, in seconds since +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. + +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_gpgsa", "gps_gprmc", and "gps_gpgga" sensors. Location +information can be parsed out of the "gps_gpgga" sensor by using gpsd or +another NMEA parser. |