14 Aug 2004 3 3 The GPSD Project GPSD Documentation libgpsd service library for GPS applications C: #include <gpsd.h> int gpsd_open_dgps char * dgpsserver void gpsd_init struct gps_device_t *session struct * gps_context_t * char * device int gpsd_activate struct gps_device_t *session void gpsd_deactivate struct gps_device_t * session gps_mask_t gpsd_poll struct gps_device_t * session void gpsd_wrap struct gps_device_t * session libgpsd is a service library which supports querying GPS devices; link it with the linker option -lgpsd. It is a set of low-level device-handling calls, which gpsd1 itself uses. See gpsd3 for a description of the high-level interface, which is almost certainly what you want. Calling gpsd_init() initializes a session structure to hold the data collected by the GPS. The second argument must be a context structure. The library will use it for information that need to be shared between sessions; presently this includes the leap-second correction and possibly a pointer to a shared-memory segment used to communicate with the Network Time Protocol daemon. After the session structure has been set up, you may modify some of its members. gpsd_device This member should hold the path name of the device. baudrate Communication speed in bits per second. For NMEA or SiRF devices, the library automatically hunts through all plausible baud rates, stopping on the one where it sees valid packets. By setting this field you can designate a speed to be tried at the front of the hunt queue raw_hook A hook function to be executed on each NMEA sentence or as it is read from the GPS. The data from non-NMEA GPSes like the EarthMate will be translated to an NMEA sentence before being passed to the hook. Parameters are a pointer to a gps_data structure full of parsed data, the sentence, and the length of the sentene.. gpsd_activate() initializes the connection to the GPS. gpsd_deactivate() closes the connection. These functions are provided so that long-running programs can release a connection when there is no activity requiring the GPS, and re-acquire it later. gpsd_poll() queries the GPS and updates the part of the session structure that holds position, speed, GPS signal quality, and other data returned by the GPS. It returns a mask describing which fields have changed. gpsd_wrap() ends the session, implicitly performing a gpsd_deactivate(). The calling application must define one additional function: gpsd_report(). The library will use this to issue ordinary status messages. See gpsd.h in the source distribution for the set of logging levels. The low-level functions do not allocate or free any dynamic storage. They can thus be used in a long-running application (such as gpsd8 itself) with a guarantee that they won't cause memory leaks. Writes to the context structure members are not guarded by a mutex. gpsd8, gps1, libgps3. Eric S. Raymond <esr@thyrsus.com> based partly on earlier work by Remco Treffkorn, Derrick Brashear, and Russ Nelson.