C/C++ - Compass Bricklet

This is the description of the C/C++ API bindings for the Compass Bricklet. General information and technical specifications for the Compass 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_compass.h"

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

int main(void) {
    // Create IP connection
    IPConnection ipcon;
    ipcon_create(&ipcon);

    // Create device object
    Compass c;
    compass_create(&c, 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 heading
    int16_t heading;
    if(compass_get_heading(&c, &heading) < 0) {
        fprintf(stderr, "Could not get heading, probably timeout\n");
        return 1;
    }

    printf("Heading: %f °\n", heading/10.0);

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

Callback

Download (example_callback.c)

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#include <stdio.h>

#include "ip_connection.h"
#include "bricklet_compass.h"

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

// Callback function for heading callback
void cb_heading(int16_t heading, void *user_data) {
    (void)user_data; // avoid unused parameter warning

    printf("Heading: %f °\n", heading/10.0);
}

int main(void) {
    // Create IP connection
    IPConnection ipcon;
    ipcon_create(&ipcon);

    // Create device object
    Compass c;
    compass_create(&c, 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 heading callback to function cb_heading
    compass_register_callback(&c,
                              COMPASS_CALLBACK_HEADING,
                              (void (*)(void))cb_heading,
                              NULL);

    // Set period for heading callback to 0.1s (100ms) without a threshold
    compass_set_heading_callback_configuration(&c, 100, false, 'x', 0, 0);

    printf("Press key to exit\n");
    getchar();
    compass_destroy(&c);
    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
  • E_NON_ASCII_CHAR_IN_SECRET = -14

as defined in ip_connection.h.

All functions listed below are thread-safe.

Basic Functions

void compass_create(Compass *compass, const char *uid, IPConnection *ipcon)

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

Compass compass;
compass_create(&compass, "YOUR_DEVICE_UID", &ipcon);

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

void compass_destroy(Compass *compass)

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

int compass_get_heading(Compass *compass, int16_t *ret_heading)

Returns the heading in 1/10 degree (north = 0 degree, east = 90 degree).

Alternatively you can use compass_get_magnetic_flux_density() and calculate the heading with heading = atan2(y, x) * 180 / PI.

If you want to get the value periodically, it is recommended to use the COMPASS_CALLBACK_HEADING callback. You can set the callback configuration with compass_set_heading_callback_configuration().

int compass_get_magnetic_flux_density(Compass *compass, int32_t *ret_x, int32_t *ret_y, int32_t *ret_z)

Returns the magnetic flux density (magnetic induction) for all three axis in 1/10 mG (milli Gauss).

If you want to get the value periodically, it is recommended to use the COMPASS_CALLBACK_MAGNETIC_FLUX_DENSITY callback. You can set the callback configuration with compass_set_magnetic_flux_density_callback_configuration().

int compass_set_configuration(Compass *compass, uint8_t data_rate, bool background_calibration)

Configures the data rate and background calibration.

  • Data Rate: Sets the data rate that is used by the magnetometer. The lower the data rate, the lower is the noise on the data.
  • Background Calibration: Set to true to enable the background calibration and false to turn it off. If the background calibration is enabled the sensing polarity is flipped once per second to automatically calculate and remove offset that is caused by temperature changes. This polarity flipping takes about 20ms. This means that once a second you will not get new data for a period of 20ms. We highly recommend that you keep the background calibration enabled and only disable it if the 20ms off-time is a problem in your application.

Default values: Data rate of 100Hz and background calibration enabled.

The following constants are available for this function:

  • COMPASS_DATA_RATE_100HZ = 0
  • COMPASS_DATA_RATE_200HZ = 1
  • COMPASS_DATA_RATE_400HZ = 2
  • COMPASS_DATA_RATE_600HZ = 3
int compass_get_configuration(Compass *compass, uint8_t *ret_data_rate, bool *ret_background_calibration)

Returns the configuration as set by compass_set_configuration().

The following constants are available for this function:

  • COMPASS_DATA_RATE_100HZ = 0
  • COMPASS_DATA_RATE_200HZ = 1
  • COMPASS_DATA_RATE_400HZ = 2
  • COMPASS_DATA_RATE_600HZ = 3

Advanced Functions

int compass_set_calibration(Compass *compass, int16_t offset[3], int16_t gain[3])

Sets offset and gain for each of the three axes.

The Bricklet is factory calibrated. If you want to re-calibrate the Bricklet we recommend that you do the calibration through Brick Viewer.

The calibration is saved in non-volatile memory and only has to be done once.

int compass_get_calibration(Compass *compass, int16_t ret_offset[3], int16_t ret_gain[3])

Returns the calibration parameters as set by compass_set_calibration().

int compass_get_api_version(Compass *compass, 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 compass_get_response_expected(Compass *compass, 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 compass_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.

The following constants are available for this function:

  • COMPASS_FUNCTION_SET_HEADING_CALLBACK_CONFIGURATION = 2
  • COMPASS_FUNCTION_SET_MAGNETIC_FLUX_DENSITY_CALLBACK_CONFIGURATION = 6
  • COMPASS_FUNCTION_SET_CONFIGURATION = 9
  • COMPASS_FUNCTION_SET_CALIBRATION = 11
  • COMPASS_FUNCTION_SET_WRITE_FIRMWARE_POINTER = 237
  • COMPASS_FUNCTION_SET_STATUS_LED_CONFIG = 239
  • COMPASS_FUNCTION_RESET = 243
  • COMPASS_FUNCTION_WRITE_UID = 248
int compass_set_response_expected(Compass *compass, 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 constants are available for this function:

  • COMPASS_FUNCTION_SET_HEADING_CALLBACK_CONFIGURATION = 2
  • COMPASS_FUNCTION_SET_MAGNETIC_FLUX_DENSITY_CALLBACK_CONFIGURATION = 6
  • COMPASS_FUNCTION_SET_CONFIGURATION = 9
  • COMPASS_FUNCTION_SET_CALIBRATION = 11
  • COMPASS_FUNCTION_SET_WRITE_FIRMWARE_POINTER = 237
  • COMPASS_FUNCTION_SET_STATUS_LED_CONFIG = 239
  • COMPASS_FUNCTION_RESET = 243
  • COMPASS_FUNCTION_WRITE_UID = 248
int compass_set_response_expected_all(Compass *compass, bool response_expected)

Changes the response expected flag for all setter and callback configuration functions of this device at once.

int compass_get_spitfp_error_count(Compass *compass, uint32_t *ret_error_count_ack_checksum, uint32_t *ret_error_count_message_checksum, uint32_t *ret_error_count_frame, uint32_t *ret_error_count_overflow)

Returns the error count for the communication between Brick and Bricklet.

The errors are divided into

  • ACK checksum errors,
  • message checksum errors,
  • framing errors and
  • overflow errors.

The errors counts are for errors that occur on the Bricklet side. All Bricks have a similar function that returns the errors on the Brick side.

int compass_set_bootloader_mode(Compass *compass, uint8_t mode, uint8_t *ret_status)

Sets the bootloader mode and returns the status after the requested mode change was instigated.

You can change from bootloader mode to firmware mode and vice versa. A change from bootloader mode to firmware mode will only take place if the entry function, device identifier and CRC are present and correct.

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

The following constants are available for this function:

  • COMPASS_BOOTLOADER_MODE_BOOTLOADER = 0
  • COMPASS_BOOTLOADER_MODE_FIRMWARE = 1
  • COMPASS_BOOTLOADER_MODE_BOOTLOADER_WAIT_FOR_REBOOT = 2
  • COMPASS_BOOTLOADER_MODE_FIRMWARE_WAIT_FOR_REBOOT = 3
  • COMPASS_BOOTLOADER_MODE_FIRMWARE_WAIT_FOR_ERASE_AND_REBOOT = 4
  • COMPASS_BOOTLOADER_STATUS_OK = 0
  • COMPASS_BOOTLOADER_STATUS_INVALID_MODE = 1
  • COMPASS_BOOTLOADER_STATUS_NO_CHANGE = 2
  • COMPASS_BOOTLOADER_STATUS_ENTRY_FUNCTION_NOT_PRESENT = 3
  • COMPASS_BOOTLOADER_STATUS_DEVICE_IDENTIFIER_INCORRECT = 4
  • COMPASS_BOOTLOADER_STATUS_CRC_MISMATCH = 5
int compass_get_bootloader_mode(Compass *compass, uint8_t *ret_mode)

Returns the current bootloader mode, see compass_set_bootloader_mode().

The following constants are available for this function:

  • COMPASS_BOOTLOADER_MODE_BOOTLOADER = 0
  • COMPASS_BOOTLOADER_MODE_FIRMWARE = 1
  • COMPASS_BOOTLOADER_MODE_BOOTLOADER_WAIT_FOR_REBOOT = 2
  • COMPASS_BOOTLOADER_MODE_FIRMWARE_WAIT_FOR_REBOOT = 3
  • COMPASS_BOOTLOADER_MODE_FIRMWARE_WAIT_FOR_ERASE_AND_REBOOT = 4
int compass_set_write_firmware_pointer(Compass *compass, uint32_t pointer)

Sets the firmware pointer for compass_write_firmware(). The pointer has to be increased by chunks of size 64. The data is written to flash every 4 chunks (which equals to one page of size 256).

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

int compass_write_firmware(Compass *compass, uint8_t data[64], uint8_t *ret_status)

Writes 64 Bytes of firmware at the position as written by compass_set_write_firmware_pointer() before. The firmware is written to flash every 4 chunks.

You can only write firmware in bootloader mode.

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

int compass_set_status_led_config(Compass *compass, uint8_t config)

Sets the status LED configuration. By default the LED shows communication traffic between Brick and Bricklet, it flickers once for every 10 received data packets.

You can also turn the LED permanently on/off or show a heartbeat.

If the Bricklet is in bootloader mode, the LED is will show heartbeat by default.

The following constants are available for this function:

  • COMPASS_STATUS_LED_CONFIG_OFF = 0
  • COMPASS_STATUS_LED_CONFIG_ON = 1
  • COMPASS_STATUS_LED_CONFIG_SHOW_HEARTBEAT = 2
  • COMPASS_STATUS_LED_CONFIG_SHOW_STATUS = 3
int compass_get_status_led_config(Compass *compass, uint8_t *ret_config)

Returns the configuration as set by compass_set_status_led_config()

The following constants are available for this function:

  • COMPASS_STATUS_LED_CONFIG_OFF = 0
  • COMPASS_STATUS_LED_CONFIG_ON = 1
  • COMPASS_STATUS_LED_CONFIG_SHOW_HEARTBEAT = 2
  • COMPASS_STATUS_LED_CONFIG_SHOW_STATUS = 3
int compass_get_chip_temperature(Compass *compass, int16_t *ret_temperature)

Returns the temperature in °C as measured inside the microcontroller. The value returned is not the ambient temperature!

The temperature is only proportional to the real temperature and it has bad accuracy. Practically it is only useful as an indicator for temperature changes.

int compass_reset(Compass *compass)

Calling this function will reset the Bricklet. All configurations will be lost.

After a reset you have to create new device objects, calling functions on the existing ones will result in undefined behavior!

int compass_write_uid(Compass *compass, uint32_t uid)

Writes a new UID into flash. If you want to set a new UID you have to decode the Base58 encoded UID string into an integer first.

We recommend that you use Brick Viewer to change the UID.

int compass_read_uid(Compass *compass, uint32_t *ret_uid)

Returns the current UID as an integer. Encode as Base58 to get the usual string version.

int compass_get_identity(Compass *compass, 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 compass_register_callback(Compass *compass, 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 compass_set_heading_callback_configuration(Compass *compass, uint32_t period, bool value_has_to_change, char option, int16_t min, int16_t max)

The period in ms is the period with which the COMPASS_CALLBACK_HEADING callback is triggered periodically. A value of 0 turns the callback off.

If the value has to change-parameter is set to true, the callback is only triggered after the value has changed. If the value didn't change within the period, the callback is triggered immediately on change.

If it is set to false, the callback is continuously triggered with the period, independent of the value.

It is furthermore possible to constrain the callback with thresholds.

The option-parameter together with min/max sets a threshold for the COMPASS_CALLBACK_HEADING callback.

The following options are possible:

Option Description
'x' Threshold is turned off
'o' Threshold is triggered when the value is outside the min and max values
'i' Threshold is triggered when the value is inside or equal to the min and max values
'<' Threshold is triggered when the value is smaller than the min value (max is ignored)
'>' Threshold is triggered when the value is greater than the min value (max is ignored)

If the option is set to 'x' (threshold turned off) the callback is triggered with the fixed period.

The default value is (0, false, 'x', 0, 0).

The following constants are available for this function:

  • COMPASS_THRESHOLD_OPTION_OFF = 'x'
  • COMPASS_THRESHOLD_OPTION_OUTSIDE = 'o'
  • COMPASS_THRESHOLD_OPTION_INSIDE = 'i'
  • COMPASS_THRESHOLD_OPTION_SMALLER = '<'
  • COMPASS_THRESHOLD_OPTION_GREATER = '>'
int compass_get_heading_callback_configuration(Compass *compass, uint32_t *ret_period, bool *ret_value_has_to_change, char *ret_option, int16_t *ret_min, int16_t *ret_max)

Returns the callback configuration as set by compass_set_heading_callback_configuration().

The following constants are available for this function:

  • COMPASS_THRESHOLD_OPTION_OFF = 'x'
  • COMPASS_THRESHOLD_OPTION_OUTSIDE = 'o'
  • COMPASS_THRESHOLD_OPTION_INSIDE = 'i'
  • COMPASS_THRESHOLD_OPTION_SMALLER = '<'
  • COMPASS_THRESHOLD_OPTION_GREATER = '>'
int compass_set_magnetic_flux_density_callback_configuration(Compass *compass, uint32_t period, bool value_has_to_change)

The period in ms is the period with which the COMPASS_CALLBACK_MAGNETIC_FLUX_DENSITY callback is triggered periodically. A value of 0 turns the callback off.

If the value has to change-parameter is set to true, the callback is only triggered after the value has changed. If the value didn't change within the period, the callback is triggered immediately on change.

If it is set to false, the callback is continuously triggered with the period, independent of the value.

The default value is (0, false).

int compass_get_magnetic_flux_density_callback_configuration(Compass *compass, uint32_t *ret_period, bool *ret_value_has_to_change)

Returns the callback configuration as set by compass_set_magnetic_flux_density_callback_configuration().

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the compass_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);
}

compass_register_callback(&compass, COMPASS_CALLBACK_EXAMPLE, (void (*)(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.

COMPASS_CALLBACK_HEADING
void callback(int16_t heading, void *user_data)

This callback is triggered periodically according to the configuration set by compass_set_heading_callback_configuration().

The parameter is the same as compass_get_heading().

COMPASS_CALLBACK_MAGNETIC_FLUX_DENSITY
void callback(int32_t x, int32_t y, int32_t z, void *user_data)

This callback is triggered periodically according to the configuration set by compass_set_magnetic_flux_density_callback_configuration().

The parameters are the same as compass_get_magnetic_flux_density().

Constants

COMPASS_DEVICE_IDENTIFIER

This constant is used to identify a Compass Bricklet.

The compass_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.

COMPASS_DEVICE_DISPLAY_NAME

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