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:breadcrumbs: <a href="../../index.html">Home</a> / <a href="../../index.html#software-c">Software</a> / C/C++ - Hall Effect Bricklet

.. |device_identifier_constant| replace:: There is also a :ref:`constant <hall_effect_bricklet_c_constants>` for the device identifier of this Bricklet.

.. _hall_effect_bricklet_c:

C/C++ - Hall Effect Bricklet
============================

This is the description of the :ref:`C/C++ API bindings <api_bindings_c>` for the :ref:`Hall Effect Bricklet <hall_effect_bricklet>`. General information and technical
specifications for the Hall Effect Bricklet are summarized in its :ref:`hardware description
<hall_effect_bricklet_description>`.

An :ref:`installation guide <api_bindings_c_install>` for the C/C++ API
bindings is part of their general description.

.. _hall_effect_bricklet_c_examples:


Examples
--------

The example code below is `Public Domain (CC0 1.0)
<http://creativecommons.org/publicdomain/zero/1.0/>`__.

Simple
^^^^^^

`Download (example_simple.c) <https://github.com/Tinkerforge/hall-effect-bricklet/raw/master/software/examples/c/example_simple.c>`__

.. literalinclude:: HallEffect_Bricklet_C_example_simple.c
 :language: c
 :linenos:
 :tab-width: 4

Callback
^^^^^^^^

`Download (example_callback.c) <https://github.com/Tinkerforge/hall-effect-bricklet/raw/master/software/examples/c/example_callback.c>`__

.. literalinclude:: HallEffect_Bricklet_C_example_callback.c
 :language: c
 :linenos:
 :tab-width: 4

.. _hall_effect_bricklet_c_api:

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 :file:`ip_connection.h`.

All functions listed below are thread-safe.




Basic Functions
^^^^^^^^^^^^^^^


.. c:function:: 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``:

 .. code-block:: c

    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 :ref:`above <hall_effect_bricklet_c_examples>`).

.. c:function:: 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.


.. c:function:: 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.
 
.. c:function:: 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
 :c:func:`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
^^^^^^^^^^^^^^^^^^

.. c:function:: 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
 
.. c:function:: 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 :c:func:`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
 
.. c:function:: 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.
 
.. c:function:: 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
 :c:func:`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 :c:func:`hall_effect_set_response_expected`
 for the list of function ID defines available for this function.
 
.. c: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
 
.. c:function:: 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.
 
.. c:function:: 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 :ref:`here <device_identifier>`.
 |device_identifier_constant|
 


Callback Configuration Functions
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


.. c:function:: 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
 :ref:`below <hall_effect_bricklet_c_callbacks>`.


.. c:function:: 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.
 
.. c:function:: int hall_effect_get_edge_interrupt(HallEffect *hall_effect, uint32_t *ret_edges)

 Returns the edges as set by :c:func:`hall_effect_set_edge_interrupt`.
 
.. c:function:: int hall_effect_set_edge_count_callback_period(HallEffect *hall_effect, uint32_t period)

 Sets the period in ms with which the :c:data:`HALL_EFFECT_CALLBACK_EDGE_COUNT` callback is triggered
 periodically. A value of 0 turns the callback off.
 
 :c:data:`HALL_EFFECT_CALLBACK_EDGE_COUNT` is only triggered if the edge count has changed since the
 last triggering.
 
 The default value is 0.
 
.. c:function:: int hall_effect_get_edge_count_callback_period(HallEffect *hall_effect, uint32_t *ret_period)

 Returns the period as set by :c:func:`hall_effect_set_edge_count_callback_period`.
 


.. _hall_effect_bricklet_c_callbacks:

Callbacks
^^^^^^^^^

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

 .. code-block:: c

    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.

.. c:var:: HALL_EFFECT_CALLBACK_EDGE_COUNT

 .. code-block:: c

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


 This callback is triggered periodically with the period that is set by
 :c:func:`hall_effect_set_edge_count_callback_period`. The parameters are the
 current count and the current value (see :c:func:`hall_effect_get_value` and :c:func:`hall_effect_get_edge_count`).
 
 :c:data:`HALL_EFFECT_CALLBACK_EDGE_COUNT` is only triggered if the count or value changed since the
 last triggering.
 


.. _hall_effect_bricklet_c_constants:

Constants
^^^^^^^^^

.. c:var:: HALL_EFFECT_DEVICE_IDENTIFIER

 This constant is used to identify a Hall Effect Bricklet.

 The :c:func:`hall_effect_get_identity` function and the :c:data:`IPCON_CALLBACK_ENUMERATE`
 callback of the IP Connection have a ``device_identifier`` parameter to specify
 the Brick's or Bricklet's type.

