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:breadcrumbs: <a href="../../index.html">Home</a> / <a href="../../index.html#software-c">Software</a> / C/C++ - GPS Bricklet

.. |device_identifier_constant| replace:: There is also a :ref:`constant <gps_bricklet_c_constants>` for the device identifier of this Bricklet.

.. _gps_bricklet_c:

C/C++ - GPS Bricklet
====================

This is the description of the :ref:`C/C++ API bindings <api_bindings_c>` for the :ref:`GPS Bricklet <gps_bricklet>`. General information and technical
specifications for the GPS Bricklet are summarized in its :ref:`hardware description
<gps_bricklet_description>`.

An :ref:`installation guide <api_bindings_c_install>` for the C/C++ API
bindings is part of their general description.

.. _gps_bricklet_c_examples:


Examples
--------

The example code below is `Public Domain (CC0 1.0)
<http://creativecommons.org/publicdomain/zero/1.0/>`__.

Simple
^^^^^^

`Download (example_simple.c) <https://github.com/Tinkerforge/gps-bricklet/raw/master/software/examples/c/example_simple.c>`__

.. literalinclude:: GPS_Bricklet_C_example_simple.c
 :language: c
 :linenos:
 :tab-width: 4

Callback
^^^^^^^^

`Download (example_callback.c) <https://github.com/Tinkerforge/gps-bricklet/raw/master/software/examples/c/example_callback.c>`__

.. literalinclude:: GPS_Bricklet_C_example_callback.c
 :language: c
 :linenos:
 :tab-width: 4

.. _gps_bricklet_c_api:

API
---

Every function of the C/C++ bindings returns an integer which describes an
error code. Data returned from the device, when a getter is called,
is handled via call by reference. These parameters are labeled with the
``ret_`` prefix.

Possible error codes are:

* E_OK = 0
* E_TIMEOUT = -1
* E_NO_STREAM_SOCKET = -2
* E_HOSTNAME_INVALID = -3
* E_NO_CONNECT = -4
* E_NO_THREAD = -5
* E_NOT_ADDED = -6 (unused since bindings version 2.0.0)
* E_ALREADY_CONNECTED = -7
* E_NOT_CONNECTED = -8
* E_INVALID_PARAMETER = -9
* E_NOT_SUPPORTED = -10
* E_UNKNOWN_ERROR_CODE = -11

as defined in :file:`ip_connection.h`.

All functions listed below are thread-safe.




Basic Functions
^^^^^^^^^^^^^^^


.. c:function:: void gps_create(GPS *gps, const char *uid, IPConnection *ipcon)

 Creates the device object ``gps`` with the unique device ID ``uid`` and adds
 it to the IPConnection ``ipcon``:

 .. code-block:: c

    GPS gps;
    gps_create(&gps, "YOUR_DEVICE_UID", &ipcon);

 This device object can be used after the IP connection has been connected
 (see examples :ref:`above <gps_bricklet_c_examples>`).

.. c:function:: void gps_destroy(GPS *gps)

 Removes the device object ``gps`` from its IPConnection and destroys it.
 The device object cannot be used anymore afterwards.


.. c:function:: int gps_get_coordinates(GPS *gps, uint32_t *ret_latitude, char *ret_ns, uint32_t *ret_longitude, char *ret_ew, uint16_t *ret_pdop, uint16_t *ret_hdop, uint16_t *ret_vdop, uint16_t *ret_epe)

 Returns the GPS coordinates. Latitude and longitude are given in the
 ``DD.dddddd°`` format, the value 57123468 means 57.123468°.
 The parameter ``ns`` and ``ew`` are the cardinal directions for
 latitude and longitude. Possible values for ``ns`` and ``ew`` are 'N', 'S', 'E'
 and 'W' (north, south, east and west).
 
 PDOP, HDOP and VDOP are the dilution of precision (DOP) values. They specify
 the additional multiplicative effect of GPS satellite geometry on GPS 
 precision. See 
 `here <http://en.wikipedia.org/wiki/Dilution_of_precision_(GPS)>`__
 for more information. The values are give in hundredths.
 
 EPE is the "Estimated Position Error". The EPE is given in cm. This is not the
 absolute maximum error, it is the error with a specific confidence. See
 `here <http://www.nps.gov/gis/gps/WhatisEPE.html>`__ for more information.
 
 This data is only valid if there is currently a fix as indicated by
 :c:func:`gps_get_status`.
 
.. c:function:: int gps_get_status(GPS *gps, uint8_t *ret_fix, uint8_t *ret_satellites_view, uint8_t *ret_satellites_used)

 Returns the current fix status, the number of satellites that are in view and
 the number of satellites that are currently used.
 
 Possible fix status values can be:
 
 .. csv-table::
  :header: "Value", "Description"
  :widths: 10, 100
 
  "1", "No Fix, :c:func:`gps_get_coordinates` and :c:func:`gps_get_altitude` return invalid data"
  "2", "2D Fix, only :c:func:`gps_get_coordinates` returns valid data"
  "3", "3D Fix, :c:func:`gps_get_coordinates` and :c:func:`gps_get_altitude` return valid data"
 
 There is also a :ref:`blue LED <gps_bricklet_fix_led>` on the Bricklet that
 indicates the fix status.
 
 The following defines are available for this function:
 
 * GPS_FIX_NO_FIX = 1
 * GPS_FIX_2D_FIX = 2
 * GPS_FIX_3D_FIX = 3
 
.. c:function:: int gps_get_altitude(GPS *gps, uint32_t *ret_altitude, uint32_t *ret_geoidal_separation)

 Returns the current altitude and corresponding geoidal separation.
 
 Both values are given in cm.
 
 This data is only valid if there is currently a fix as indicated by
 :c:func:`gps_get_status`.
 
.. c:function:: int gps_get_motion(GPS *gps, uint32_t *ret_course, uint32_t *ret_speed)

 Returns the current course and speed. Course is given in hundredths degree
 and speed is given in hundredths km/h. A course of 0° means the Bricklet is
 traveling north bound and 90° means it is traveling east bound.
 
 Please note that this only returns useful values if an actual movement
 is present.
 
 This data is only valid if there is currently a fix as indicated by
 :c:func:`gps_get_status`.
 
.. c:function:: int gps_get_date_time(GPS *gps, uint32_t *ret_date, uint32_t *ret_time)

 Returns the current date and time. The date is
 given in the format ``ddmmyy`` and the time is given
 in the format ``hhmmss.sss``. For example, 140713 means
 14.05.13 as date and 195923568 means 19:59:23.568 as time.
 


Advanced Functions
^^^^^^^^^^^^^^^^^^

.. c:function:: int gps_restart(GPS *gps, uint8_t restart_type)

 Restarts the GPS Bricklet, the following restart types are available:
 
 .. csv-table::
  :header: "Value", "Description"
  :widths: 10, 100
 
  "0", "Hot start (use all available data in the NV store)"
  "1", "Warm start (don't use ephemeris at restart)"
  "2", "Cold start (don't use time, position, almanacs and ephemeris at restart)"
  "3", "Factory reset (clear all system/user configurations at restart)"
 
 The following defines are available for this function:
 
 * GPS_RESTART_TYPE_HOT_START = 0
 * GPS_RESTART_TYPE_WARM_START = 1
 * GPS_RESTART_TYPE_COLD_START = 2
 * GPS_RESTART_TYPE_FACTORY_RESET = 3
 
.. c:function:: int gps_get_api_version(GPS *gps, uint8_t ret_api_version[3])

 Returns the version of the API definition (major, minor, revision) implemented
 by this API bindings. This is neither the release version of this API bindings
 nor does it tell you anything about the represented Brick or Bricklet.
 
.. c:function:: int gps_get_response_expected(GPS *gps, uint8_t function_id, bool *ret_response_expected)

 Returns the response expected flag for the function specified by the function
 ID parameter. It is *true* if the function is expected to send a response,
 *false* otherwise.
 
 For getter functions this is enabled by default and cannot be disabled,
 because those functions will always send a response. For callback configuration
 functions it is enabled by default too, but can be disabled by
 :c:func:`gps_set_response_expected`. For setter functions it is disabled by default
 and can be enabled.
 
 Enabling the response expected flag for a setter function allows to detect
 timeouts and other error conditions calls of this setter as well. The
 device will then send a response for this purpose. If this flag is disabled for
 a setter function then no response is send and errors are silently ignored,
 because they cannot be detected.
 
 See :c:func:`gps_set_response_expected`
 for the list of function ID defines available for this function.
 
.. c:function:: int gps_set_response_expected(GPS *gps, uint8_t function_id, bool response_expected)

 Changes the response expected flag of the function specified by the
 function ID parameter. This flag can only be changed for setter (default value:
 *false*) and callback configuration functions (default value: *true*). For
 getter functions it is always enabled and callbacks it is always disabled.
 
 Enabling the response expected flag for a setter function allows to detect
 timeouts and other error conditions calls of this setter as well. The
 device will then send a response for this purpose. If this flag is disabled for
 a setter function then no response is send and errors are silently ignored,
 because they cannot be detected.
 
 The following function ID defines are available for this function:
 
 * GPS_FUNCTION_RESTART = 6
 * GPS_FUNCTION_SET_COORDINATES_CALLBACK_PERIOD = 7
 * GPS_FUNCTION_SET_STATUS_CALLBACK_PERIOD = 9
 * GPS_FUNCTION_SET_ALTITUDE_CALLBACK_PERIOD = 11
 * GPS_FUNCTION_SET_MOTION_CALLBACK_PERIOD = 13
 * GPS_FUNCTION_SET_DATE_TIME_CALLBACK_PERIOD = 15
 
.. c:function:: int gps_set_response_expected_all(GPS *gps, bool response_expected)

 Changes the response expected flag for all setter and callback configuration
 functions of this device at once.
 
.. c:function:: int gps_get_identity(GPS *gps, char ret_uid[8], char ret_connected_uid[8], char *ret_position, uint8_t ret_hardware_version[3], uint8_t ret_firmware_version[3], uint16_t *ret_device_identifier)

 Returns the UID, the UID where the Bricklet is connected to, 
 the position, the hardware and firmware version as well as the
 device identifier.
 
 The position can be 'a', 'b', 'c' or 'd'.
 
 The device identifier numbers can be found :ref:`here <device_identifier>`.
 |device_identifier_constant|
 


Callback Configuration Functions
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


.. c:function:: void gps_register_callback(GPS *gps, uint8_t id, void *callback, void *user_data)

 Registers a callback with ID ``id`` to the function ``callback``. The
 ``user_data`` will be given as a parameter of the callback.

 The available IDs with corresponding function signatures are listed
 :ref:`below <gps_bricklet_c_callbacks>`.


.. c:function:: int gps_set_coordinates_callback_period(GPS *gps, uint32_t period)

 Sets the period in ms with which the :c:data:`GPS_CALLBACK_COORDINATES` callback is triggered
 periodically. A value of 0 turns the callback off.
 
 :c:data:`GPS_CALLBACK_COORDINATES` is only triggered if the coordinates changed since the
 last triggering.
 
 The default value is 0.
 
.. c:function:: int gps_get_coordinates_callback_period(GPS *gps, uint32_t *ret_period)

 Returns the period as set by :c:func:`gps_set_coordinates_callback_period`.
 
.. c:function:: int gps_set_status_callback_period(GPS *gps, uint32_t period)

 Sets the period in ms with which the :c:data:`GPS_CALLBACK_STATUS` callback is triggered
 periodically. A value of 0 turns the callback off.
 
 :c:data:`GPS_CALLBACK_STATUS` is only triggered if the status changed since the
 last triggering.
 
 The default value is 0.
 
.. c:function:: int gps_get_status_callback_period(GPS *gps, uint32_t *ret_period)

 Returns the period as set by :c:func:`gps_set_status_callback_period`.
 
.. c:function:: int gps_set_altitude_callback_period(GPS *gps, uint32_t period)

 Sets the period in ms with which the :c:data:`GPS_CALLBACK_ALTITUDE` callback is triggered
 periodically. A value of 0 turns the callback off.
 
 :c:data:`GPS_CALLBACK_ALTITUDE` is only triggered if the altitude changed since the
 last triggering.
 
 The default value is 0.
 
.. c:function:: int gps_get_altitude_callback_period(GPS *gps, uint32_t *ret_period)

 Returns the period as set by :c:func:`gps_set_altitude_callback_period`.
 
.. c:function:: int gps_set_motion_callback_period(GPS *gps, uint32_t period)

 Sets the period in ms with which the :c:data:`GPS_CALLBACK_MOTION` callback is triggered
 periodically. A value of 0 turns the callback off.
 
 :c:data:`GPS_CALLBACK_MOTION` is only triggered if the motion changed since the
 last triggering.
 
 The default value is 0.
 
.. c:function:: int gps_get_motion_callback_period(GPS *gps, uint32_t *ret_period)

 Returns the period as set by :c:func:`gps_set_motion_callback_period`.
 
.. c:function:: int gps_set_date_time_callback_period(GPS *gps, uint32_t period)

 Sets the period in ms with which the :c:data:`GPS_CALLBACK_DATE_TIME` callback is triggered
 periodically. A value of 0 turns the callback off.
 
 :c:data:`GPS_CALLBACK_DATE_TIME` is only triggered if the date or time changed since the
 last triggering.
 
 The default value is 0.
 
.. c:function:: int gps_get_date_time_callback_period(GPS *gps, uint32_t *ret_period)

 Returns the period as set by :c:func:`gps_set_date_time_callback_period`.
 


.. _gps_bricklet_c_callbacks:

Callbacks
^^^^^^^^^

Callbacks can be registered to receive
time critical or recurring data from the device. The registration is done
with the :c:func:`gps_register_callback` function. The parameters consist of
the device object, the callback ID, the callback function and optional
user data:

 .. code-block:: c

    void my_callback(int p, void *user_data) {
        printf("parameter: %d\n", p);
    }

    gps_register_callback(&gps, GPS_CALLBACK_EXAMPLE, (void *)my_callback, NULL);

The available constants with corresponding callback function signatures
are described below.

.. note::
 Using callbacks for recurring events is *always* preferred
 compared to using getters. It will use less USB bandwidth and the latency
 will be a lot better, since there is no round trip time.

.. c:var:: GPS_CALLBACK_COORDINATES

 .. code-block:: c

  void callback(uint32_t latitude, char ns, uint32_t longitude, char ew, uint16_t pdop, uint16_t hdop, uint16_t vdop, uint16_t epe, void *user_data)


 This callback is triggered periodically with the period that is set by
 :c:func:`gps_set_coordinates_callback_period`. The parameters are the same
 as for :c:func:`gps_get_coordinates`.
 
 :c:data:`GPS_CALLBACK_COORDINATES` is only triggered if the coordinates changed since the
 last triggering and if there is currently a fix as indicated by
 :c:func:`gps_get_status`.
 
.. c:var:: GPS_CALLBACK_STATUS

 .. code-block:: c

  void callback(uint8_t fix, uint8_t satellites_view, uint8_t satellites_used, void *user_data)


 This callback is triggered periodically with the period that is set by
 :c:func:`gps_set_status_callback_period`. The parameters are the same
 as for :c:func:`gps_get_status`.
 
 :c:data:`GPS_CALLBACK_STATUS` is only triggered if the status changed since the
 last triggering.
 
 The following defines are available for this function:
 
 * GPS_FIX_NO_FIX = 1
 * GPS_FIX_2D_FIX = 2
 * GPS_FIX_3D_FIX = 3
 
.. c:var:: GPS_CALLBACK_ALTITUDE

 .. code-block:: c

  void callback(uint32_t altitude, uint32_t geoidal_separation, void *user_data)


 This callback is triggered periodically with the period that is set by
 :c:func:`gps_set_altitude_callback_period`. The parameters are the same
 as for :c:func:`gps_get_altitude`.
 
 :c:data:`GPS_CALLBACK_ALTITUDE` is only triggered if the altitude changed since the
 last triggering and if there is currently a fix as indicated by
 :c:func:`gps_get_status`.
 
.. c:var:: GPS_CALLBACK_MOTION

 .. code-block:: c

  void callback(uint32_t course, uint32_t speed, void *user_data)


 This callback is triggered periodically with the period that is set by
 :c:func:`gps_set_motion_callback_period`. The parameters are the same
 as for :c:func:`gps_get_motion`.
 
 :c:data:`GPS_CALLBACK_MOTION` is only triggered if the motion changed since the
 last triggering and if there is currently a fix as indicated by
 :c:func:`gps_get_status`.
 
.. c:var:: GPS_CALLBACK_DATE_TIME

 .. code-block:: c

  void callback(uint32_t date, uint32_t time, void *user_data)


 This callback is triggered periodically with the period that is set by
 :c:func:`gps_set_date_time_callback_period`. The parameters are the same
 as for :c:func:`gps_get_date_time`.
 
 :c:data:`GPS_CALLBACK_DATE_TIME` is only triggered if the date or time changed since the
 last triggering.
 


.. _gps_bricklet_c_constants:

Constants
^^^^^^^^^

.. c:var:: GPS_DEVICE_IDENTIFIER

 This constant is used to identify a GPS Bricklet.

 The :c:func:`gps_get_identity` function and the :c:data:`IPCON_CALLBACK_ENUMERATE`
 callback of the IP Connection have a ``device_identifier`` parameter to specify
 the Brick's or Bricklet's type.

