C/C++ - GPS Bricklet – Tinkerforge

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# C/C++ - GPS Bricklet

This is the description of the C/C++ API bindings for the GPS Bricklet. General information and technical specifications for the GPS Bricklet are summarized in its hardware description.

An installation guide for the C/C++ API bindings is part of their general description.

## Examples

The example code below is Public Domain (CC0 1.0).

### Simple

Download (example_simple.c)

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    #include <stdio.h>

    #include "ip_connection.h"
    #include "bricklet_gps.h"

    #define HOST "localhost"
    #define PORT 4223
    #define UID "ABC" // Change to your UID

    int main() {
        // Create ip connection to brickd
        IPConnection ipcon;
        ipcon_create(&ipcon);

        // Create device object
        GPS gps;
        gps_create(&gps, UID, &ipcon);

        // Connect to brickd
        if(ipcon_connect(&ipcon, HOST, PORT) < 0) {
            fprintf(stderr, "Could not connect\n");
            exit(1);
        }
        // Don't use device before ipcon is connected

        // Get current coordinates
        uint32_t ret_latitude, ret_longitude;
        char ret_ns, ret_ew;
        uint16_t ret_pdop, ret_hdop, ret_vdop, ret_epe;
        if(gps_get_coordinates(&gps,
                               &ret_latitude, &ret_ns, &ret_longitude, &ret_ew,
                               &ret_pdop, &ret_hdop, &ret_vdop, &ret_epe) < 0) {
            fprintf(stderr, "Could not get value, probably timeout\n");
            exit(1);
        }

        printf("Latitude: %f° %c\n", ret_latitude/1000000.0, ret_ns);
        printf("Longiutde: %f° %c\n", ret_longitude/1000000.0, ret_ew);

        printf("Press key to exit\n");
        getchar();
        ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
    }

### Callback

Download (example_callback.c)

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    #include <stdio.h>

    #include "ip_connection.h"
    #include "bricklet_gps.h"

    #define HOST "localhost"
    #define PORT 4223
    #define UID "ABC" // Change to your UID

    // Callback function for current callback (parameter has unit mA)
    void cb_coordinates(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) {
        (void)pdop; (void)hdop; (void)vdop; (void)epe;
        (void)user_data;

        printf("Latitude: %f° %c\n", latitude/1000000.0, ns);
        printf("Longiutde: %f° %c\n", longitude/1000000.0, ew);
    }

    int main() {
        // Create ip connection to brickd
        IPConnection ipcon;
        ipcon_create(&ipcon);

        // Create device object
        GPS gps;
        gps_create(&gps, UID, &ipcon);

        // Connect to brickd
        if(ipcon_connect(&ipcon, HOST, PORT) < 0) {
            fprintf(stderr, "Could not connect\n");
            exit(1);
        }
        // Don't use device before ipcon is connected

        // Set Period for coordinates callback to 1s (1000ms)
        // Note: The callback is only called every second if the
        //       coordinates have changed since the last call!
        gps_set_coordinates_callback_period(&gps, 1000);

        // Register coordinates callback to function cb_coordinates
        gps_register_callback(&gps, GPS_CALLBACK_COORDINATES,
                              (void *)cb_coordinates, NULL);

        printf("Press key to exit\n");
        getchar();
        ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
    }

## 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 `ip_connection.h`.

All functions listed below are thread-safe.

### Basic Functions

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`:

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

  This device object can be used after the IP connection has been connected (see examples above).

void `gps_destroy`(GPS *gps)

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

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 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 for more information.

  This data is only valid if there is currently a fix as indicated by `gps_get_status()`.

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:

  Value | Description
  --- | ---
  1 | No Fix, `gps_get_coordinates()` and `gps_get_altitude()` return invalid data
  2 | 2D Fix, only `gps_get_coordinates()` returns valid data
  3 | 3D Fix, `gps_get_coordinates()` and `gps_get_altitude()` return valid data

  There is also a blue 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

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 `gps_get_status()`.

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 `gps_get_status()`.

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

int `gps_restart`(GPS *gps, uint8_t restart_type)

  Restarts the GPS Bricklet, the following restart types are available:

  Value | Description
  --- | ---
  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

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.

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 `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 `gps_set_response_expected()` for the list of function ID defines available for this 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

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.

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 here. There is also a constant for the device identifier of this Bricklet.

### Callback Configuration Functions

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 below.

int `gps_set_coordinates_callback_period`(GPS *gps, uint32_t period)

  Sets the period in ms with which the `GPS_CALLBACK_COORDINATES` callback is triggered periodically. A value of 0 turns the callback off.

  `GPS_CALLBACK_COORDINATES` is only triggered if the coordinates changed since the last triggering.

  The default value is 0.

int `gps_get_coordinates_callback_period`(GPS *gps, uint32_t *ret_period)

  Returns the period as set by `gps_set_coordinates_callback_period()`.

int `gps_set_status_callback_period`(GPS *gps, uint32_t period)

  Sets the period in ms with which the `GPS_CALLBACK_STATUS` callback is triggered periodically. A value of 0 turns the callback off.

  `GPS_CALLBACK_STATUS` is only triggered if the status changed since the last triggering.

  The default value is 0.

int `gps_get_status_callback_period`(GPS *gps, uint32_t *ret_period)

  Returns the period as set by `gps_set_status_callback_period()`.

int `gps_set_altitude_callback_period`(GPS *gps, uint32_t period)

  Sets the period in ms with which the `GPS_CALLBACK_ALTITUDE` callback is triggered periodically. A value of 0 turns the callback off.

  `GPS_CALLBACK_ALTITUDE` is only triggered if the altitude changed since the last triggering.

  The default value is 0.

int `gps_get_altitude_callback_period`(GPS *gps, uint32_t *ret_period)

  Returns the period as set by `gps_set_altitude_callback_period()`.

int `gps_set_motion_callback_period`(GPS *gps, uint32_t period)

  Sets the period in ms with which the `GPS_CALLBACK_MOTION` callback is triggered periodically. A value of 0 turns the callback off.

  `GPS_CALLBACK_MOTION` is only triggered if the motion changed since the last triggering.

  The default value is 0.

int `gps_get_motion_callback_period`(GPS *gps, uint32_t *ret_period)

  Returns the period as set by `gps_set_motion_callback_period()`.

int `gps_set_date_time_callback_period`(GPS *gps, uint32_t period)

  Sets the period in ms with which the `GPS_CALLBACK_DATE_TIME` callback is triggered periodically. A value of 0 turns the callback off.

  `GPS_CALLBACK_DATE_TIME` is only triggered if the date or time changed since the last triggering.

  The default value is 0.

int `gps_get_date_time_callback_period`(GPS *gps, uint32_t *ret_period)

  Returns the period as set by `gps_set_date_time_callback_period()`.

### Callbacks

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

>     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.

`GPS_CALLBACK_COORDINATES`

      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 `gps_set_coordinates_callback_period()`. The parameters are the same as for `gps_get_coordinates()`.

  `GPS_CALLBACK_COORDINATES` is only triggered if the coordinates changed since the last triggering and if there is currently a fix as indicated by `gps_get_status()`.

`GPS_CALLBACK_STATUS`

      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 `gps_set_status_callback_period()`. The parameters are the same as for `gps_get_status()`.

  `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

`GPS_CALLBACK_ALTITUDE`

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

  This callback is triggered periodically with the period that is set by `gps_set_altitude_callback_period()`. The parameters are the same as for `gps_get_altitude()`.

  `GPS_CALLBACK_ALTITUDE` is only triggered if the altitude changed since the last triggering and if there is currently a fix as indicated by `gps_get_status()`.

`GPS_CALLBACK_MOTION`

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

  This callback is triggered periodically with the period that is set by `gps_set_motion_callback_period()`. The parameters are the same as for `gps_get_motion()`.

  `GPS_CALLBACK_MOTION` is only triggered if the motion changed since the last triggering and if there is currently a fix as indicated by `gps_get_status()`.

`GPS_CALLBACK_DATE_TIME`

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

  This callback is triggered periodically with the period that is set by `gps_set_date_time_callback_period()`. The parameters are the same as for `gps_get_date_time()`.

  `GPS_CALLBACK_DATE_TIME` is only triggered if the date or time changed since the last triggering.

### Constants

`GPS_DEVICE_IDENTIFIER`

  This constant is used to identify a GPS Bricklet.

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

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