C/C++ - Hall Effect Bricklet – Tinkerforge

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# C/C++ - Hall Effect Bricklet

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

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

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

        // Create device object
        HallEffect he;
        hall_effect_create(&he, 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 edge count without reset
        uint32_t edge_count;
        if(hall_effect_get_edge_count(&he, false, &edge_count) < 0) {
            fprintf(stderr, "Could not get value, probably timeout\n");
            exit(1);
        }

        printf("Edge Count: %d\n", edge_count);

        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_hall_effect.h"

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

    // Callback function for edge_count callback
    void cb_edge_count(int32_t edge_count, bool value, void *user_data) {
        (void)value; // avoid unused parameter warning
        (void)user_data; // avoid unused parameter warning

        printf("Edge Count: %d\n", edge_count);
    }

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

        // Create device object
        HallEffect he;
        hall_effect_create(&he, 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 edge_count callback to 0.05s (50ms)
        // Note: The edge_count callback is only called every 50ms if the
        //       edge_count has changed since the last call!
        hall_effect_set_edge_count_callback_period(&he, 50);

        // Register edge_count callback to function cb_edge_count
        hall_effect_register_callback(&he,
                                      HALL_EFFECT_CALLBACK_EDGE_COUNT,
                                      (void *)cb_edge_count,
                                      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 `hall_effect_create`(HallEffect *hall_effect, const char *uid, IPConnection *ipcon)

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

      HallEffect hall_effect;
      hall_effect_create(&hall_effect, "YOUR_DEVICE_UID", &ipcon);

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

void `hall_effect_destroy`(HallEffect *hall_effect)

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

int `hall_effect_get_value`(HallEffect *hall_effect, bool *ret_value)

  Returns true if a magnetic field of 35 Gauss (3.5mT) or greater is detected.

int `hall_effect_get_edge_count`(HallEffect *hall_effect, bool reset_counter, uint32_t *ret_count)

  Returns the current value of the edge counter. You can configure edge type (rising, falling, both) that is counted with `hall_effect_set_edge_count_config()`.

  If you set the reset counter to true, the count is set back to 0 directly after it is read.

### Advanced Functions

int `hall_effect_set_edge_count_config`(HallEffect *hall_effect, uint8_t edge_type, uint8_t debounce)

  The edge type parameter configures if rising edges, falling edges or both are counted. Possible edge types are:

  - 0 = rising (default)
  - 1 = falling
  - 2 = both

  A magnetic field of 35 Gauss (3.5mT) or greater causes a falling edge and a magnetic field of 25 Gauss (2.5mT) or smaller causes a rising edge.

  If a magnet comes near the Bricklet the signal goes low (falling edge), if a magnet is removed from the vicinity the signal goes high (rising edge).

  The debounce time is given in ms.

  Configuring an edge counter resets its value to 0.

  If you don't know what any of this means, just leave it at default. The default configuration is very likely OK for you.

  Default values: 0 (edge type) and 100ms (debounce time)

  The following defines are available for this function:

  - HALL_EFFECT_EDGE_TYPE_RISING = 0
  - HALL_EFFECT_EDGE_TYPE_FALLING = 1
  - HALL_EFFECT_EDGE_TYPE_BOTH = 2

int `hall_effect_get_edge_count_config`(HallEffect *hall_effect, uint8_t *ret_edge_type, uint8_t *ret_debounce)

  Returns the edge type and debounce time as set by `hall_effect_set_edge_count_config()`.

  The following defines are available for this function:

  - HALL_EFFECT_EDGE_TYPE_RISING = 0
  - HALL_EFFECT_EDGE_TYPE_FALLING = 1
  - HALL_EFFECT_EDGE_TYPE_BOTH = 2

int `hall_effect_get_api_version`(HallEffect *hall_effect, 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 `hall_effect_get_response_expected`(HallEffect *hall_effect, 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 `hall_effect_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 `hall_effect_set_response_expected()` for the list of function ID defines available for this function.

int `hall_effect_set_response_expected`(HallEffect *hall_effect, 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:

  - HALL_EFFECT_FUNCTION_SET_EDGE_COUNT_CONFIG = 3
  - HALL_EFFECT_FUNCTION_SET_EDGE_INTERRUPT = 5
  - HALL_EFFECT_FUNCTION_SET_EDGE_COUNT_CALLBACK_PERIOD = 7

int `hall_effect_set_response_expected_all`(HallEffect *hall_effect, bool response_expected)

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

int `hall_effect_get_identity`(HallEffect *hall_effect, 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 `hall_effect_register_callback`(HallEffect *hall_effect, 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 `hall_effect_set_edge_interrupt`(HallEffect *hall_effect, uint32_t edges)

  Sets the number of edges until an interrupt is invoked.

  If edges is set to n, an interrupt is invoked for every n-th detected edge.

  If edges is set to 0, the interrupt is disabled.

  Default value is 0.

int `hall_effect_get_edge_interrupt`(HallEffect *hall_effect, uint32_t *ret_edges)

  Returns the edges as set by `hall_effect_set_edge_interrupt()`.

int `hall_effect_set_edge_count_callback_period`(HallEffect *hall_effect, uint32_t period)

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

  `HALL_EFFECT_CALLBACK_EDGE_COUNT` is only triggered if the edge count has changed since the last triggering.

  The default value is 0.

int `hall_effect_get_edge_count_callback_period`(HallEffect *hall_effect, uint32_t *ret_period)

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

### Callbacks

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

>     hall_effect_register_callback(&hall_effect, HALL_EFFECT_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.

`HALL_EFFECT_CALLBACK_EDGE_COUNT`

      void callback(uint32_t count, bool value, void *user_data)

  This callback is triggered periodically with the period that is set by `hall_effect_set_edge_count_callback_period()`. The parameters are the current count and the current value (see `hall_effect_get_value()` and `hall_effect_get_edge_count()`).

  `HALL_EFFECT_CALLBACK_EDGE_COUNT` is only triggered if the count or value changed since the last triggering.

### Constants

`HALL_EFFECT_DEVICE_IDENTIFIER`

  This constant is used to identify a Hall Effect Bricklet.

  The `hall_effect_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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