C/C++ - Line Bricklet

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

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

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

    // Create device object
    Line l;
    line_create(&l, 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 reflectivity
    uint16_t reflectivity;
    if(line_get_reflectivity(&l, &reflectivity) < 0) {
        fprintf(stderr, "Could not get reflectivity, probably timeout\n");
        return 1;
    }

    printf("Reflectivity: %u\n", reflectivity);

    printf("Press key to exit\n");
    getchar();
    line_destroy(&l);
    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_line.h"

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

// Callback function for reflectivity callback
void cb_reflectivity(uint16_t reflectivity, void *user_data) {
    (void)user_data; // avoid unused parameter warning

    printf("Reflectivity: %u\n", reflectivity);
}

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

    // Create device object
    Line l;
    line_create(&l, 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 reflectivity callback to function cb_reflectivity
    line_register_callback(&l,
                           LINE_CALLBACK_REFLECTIVITY,
                           (void *)cb_reflectivity,
                           NULL);

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

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

Threshold

Download (example_threshold.c)

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#include <stdio.h>

#include "ip_connection.h"
#include "bricklet_line.h"

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

// Callback function for reflectivity reached callback
void cb_reflectivity_reached(uint16_t reflectivity, void *user_data) {
    (void)user_data; // avoid unused parameter warning

    printf("Reflectivity: %u\n", reflectivity);
}

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

    // Create device object
    Line l;
    line_create(&l, 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 threshold callbacks with a debounce time of 1 second (1000ms)
    line_set_debounce_period(&l, 1000);

    // Register reflectivity reached callback to function cb_reflectivity_reached
    line_register_callback(&l,
                           LINE_CALLBACK_REFLECTIVITY_REACHED,
                           (void *)cb_reflectivity_reached,
                           NULL);

    // Configure threshold for reflectivity "greater than 2000"
    line_set_reflectivity_callback_threshold(&l, '>', 2000, 0);

    printf("Press key to exit\n");
    getchar();
    line_destroy(&l);
    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 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
  • E_STREAM_OUT_OF_SYNC = -12

as defined in ip_connection.h.

All functions listed below are thread-safe.

Basic Functions

void line_create(Line *line, const char *uid, IPConnection *ipcon)

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

Line line;
line_create(&line, "YOUR_DEVICE_UID", &ipcon);

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

void line_destroy(Line *line)

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

int line_get_reflectivity(Line *line, uint16_t *ret_reflectivity)

Returns the currently measured reflectivity. The reflectivity is a value between 0 (not reflective) and 4095 (very reflective).

Usually black has a low reflectivity while white has a high reflectivity.

If you want to get the reflectivity periodically, it is recommended to use the LINE_CALLBACK_REFLECTIVITY callback and set the period with line_set_reflectivity_callback_period().

Advanced Functions

int line_get_api_version(Line *line, 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 line_get_response_expected(Line *line, 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 line_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 line_set_response_expected() for the list of function ID defines available for this function.

int line_set_response_expected(Line *line, 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:

  • LINE_FUNCTION_SET_REFLECTIVITY_CALLBACK_PERIOD = 2
  • LINE_FUNCTION_SET_REFLECTIVITY_CALLBACK_THRESHOLD = 4
  • LINE_FUNCTION_SET_DEBOUNCE_PERIOD = 6
int line_set_response_expected_all(Line *line, bool response_expected)

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

int line_get_identity(Line *line, 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 line_register_callback(Line *line, int16_t callback_id, void *function, 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 line_set_reflectivity_callback_period(Line *line, uint32_t period)

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

The LINE_CALLBACK_REFLECTIVITY callback is only triggered if the reflectivity has changed since the last triggering.

The default value is 0.

int line_get_reflectivity_callback_period(Line *line, uint32_t *ret_period)

Returns the period as set by line_set_reflectivity_callback_period().

int line_set_reflectivity_callback_threshold(Line *line, char option, uint16_t min, uint16_t max)

Sets the thresholds for the LINE_CALLBACK_REFLECTIVITY_REACHED callback.

The following options are possible:

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

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

The following defines are available for this function:

  • LINE_THRESHOLD_OPTION_OFF = 'x'
  • LINE_THRESHOLD_OPTION_OUTSIDE = 'o'
  • LINE_THRESHOLD_OPTION_INSIDE = 'i'
  • LINE_THRESHOLD_OPTION_SMALLER = '<'
  • LINE_THRESHOLD_OPTION_GREATER = '>'
int line_get_reflectivity_callback_threshold(Line *line, char *ret_option, uint16_t *ret_min, uint16_t *ret_max)

Returns the threshold as set by line_set_reflectivity_callback_threshold().

The following defines are available for this function:

  • LINE_THRESHOLD_OPTION_OFF = 'x'
  • LINE_THRESHOLD_OPTION_OUTSIDE = 'o'
  • LINE_THRESHOLD_OPTION_INSIDE = 'i'
  • LINE_THRESHOLD_OPTION_SMALLER = '<'
  • LINE_THRESHOLD_OPTION_GREATER = '>'
int line_set_debounce_period(Line *line, uint32_t debounce)

Sets the period in ms with which the threshold callback

is triggered, if the threshold

keeps being reached.

The default value is 100.

int line_get_debounce_period(Line *line, uint32_t *ret_debounce)

Returns the debounce period as set by line_set_debounce_period().

Callbacks

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

line_register_callback(&line, LINE_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.

LINE_CALLBACK_REFLECTIVITY
void callback(uint16_t reflectivity, void *user_data)

This callback is triggered periodically with the period that is set by line_set_reflectivity_callback_period(). The parameter is the reflectivity of the sensor.

The LINE_CALLBACK_REFLECTIVITY callback is only triggered if the reflectivity has changed since the last triggering.

LINE_CALLBACK_REFLECTIVITY_REACHED
void callback(uint16_t reflectivity, void *user_data)

This callback is triggered when the threshold as set by line_set_reflectivity_callback_threshold() is reached. The parameter is the reflectivity of the sensor.

If the threshold keeps being reached, the callback is triggered periodically with the period as set by line_set_debounce_period().

Constants

LINE_DEVICE_IDENTIFIER

This constant is used to identify a Line Bricklet.

The line_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.

LINE_DEVICE_DISPLAY_NAME

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