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+========================================================================
+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
+
+**Antenna Types:**
+
+The GPSDO is capable of supplying a 3V for active GPS antennas or supporting passive antennas
+
+------------------------------------------------------------------------
+Installation instructions
+------------------------------------------------------------------------
+Installation instructions can be found here:
+`www.ettus.com/downloads/gpsdo-kit.pdf <http://www.ettus.com/downloads/gpsdo-kit.pdf>`_
+
+********************************************
+Post installation task (N-Series only)
+********************************************
+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 Notes <./sync.html>`_),
+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 --args=<optional device args> --key=gpsdo --val=internal
+
+    -- restore original setting --
+    ./usrp_burn_mb_eeprom --args=<optional device args> --key=gpsdo --val=none
+
+------------------------------------------------------------------------
+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.