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)

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
#include <stdio.h>

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

#define HOST "localhost"
#define PORT 4223
#define UID "XYZ" // Change XYZ to the UID of your GPS Bricklet

int main(void) {
    // Create IP connection
    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");
        return 1;
    }
    // Don't use device before ipcon is connected

    // Get current coordinates
    uint32_t latitude, longitude; char ns, ew; uint16_t pdop, hdop, vdop, epe;
    if(gps_get_coordinates(&gps, &latitude, &ns, &longitude, &ew, &pdop, &hdop, &vdop,
                           &epe) < 0) {
        fprintf(stderr, "Could not get coordinates, probably timeout\n");
        return 1;
    }

    printf("Latitude: %f °\n", latitude/1000000.0);
    printf("N/S: %c\n", ns);
    printf("Longitude: %f °\n", longitude/1000000.0);
    printf("E/W: %c\n", ew);

    printf("Press key to exit\n");
    getchar();
    gps_destroy(&gps);
    ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
    return 0;
}

Callback

Download (example_callback.c)

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
#include <stdio.h>

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

#define HOST "localhost"
#define PORT 4223
#define UID "XYZ" // Change XYZ to the UID of your GPS Bricklet

// Callback function for coordinates callback
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; // avoid unused parameter warning

    printf("Latitude: %f °\n", latitude/1000000.0);
    printf("N/S: %c\n", ns);
    printf("Longitude: %f °\n", longitude/1000000.0);
    printf("E/W: %c\n", ew);
    printf("\n");
}

int main(void) {
    // Create IP connection
    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");
        return 1;
    }
    // Don't use device before ipcon is connected

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

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

    printf("Press key to exit\n");
    getchar();
    gps_destroy(&gps);
    ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
    return 0;
}

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 output parameters. 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
  • E_STREAM_OUT_OF_SYNC = -12
  • E_INVALID_UID = -13

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(), gps_get_altitude() and gps_get_motion() return invalid data
2 2D Fix, only gps_get_coordinates() and gps_get_motion() return valid data
3 3D Fix, gps_get_coordinates(), gps_get_altitude() and gps_get_motion() 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, int32_t *ret_altitude, int32_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.

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, int16_t callback_id, void (*function)(void), void *user_data)

Registers the given function with the given callback_id. The user_data will be passed as the last parameter to the function.

The available callback 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.

The GPS_CALLBACK_COORDINATES callback 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.

The GPS_CALLBACK_STATUS callback 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.

The GPS_CALLBACK_ALTITUDE callback 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.

The GPS_CALLBACK_MOTION callback 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.

The GPS_CALLBACK_DATE_TIME callback 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().

The GPS_CALLBACK_COORDINATES callback 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().

The GPS_CALLBACK_STATUS callback 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(int32_t altitude, int32_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().

The GPS_CALLBACK_ALTITUDE callback 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().

The GPS_CALLBACK_MOTION callback 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().

The GPS_CALLBACK_DATE_TIME callback 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.

GPS_DEVICE_DISPLAY_NAME

This constant represents the human readable name of a GPS Bricklet.