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

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

.. _dual_relay_bricklet_c:

C/C++ - Dual Relay Bricklet
===========================

This is the description of the :ref:`C/C++ API bindings <api_bindings_c>` for the :ref:`Dual Relay Bricklet <dual_relay_bricklet>`. General information and technical
specifications for the Dual Relay Bricklet are summarized in its :ref:`hardware description
<dual_relay_bricklet_description>`.

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

.. _dual_relay_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/dual-relay-bricklet/raw/master/software/examples/c/example_simple.c>`__

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

.. _dual_relay_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 dual_relay_create(DualRelay *dual_relay, const char *uid, IPConnection *ipcon)

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

 .. code-block:: c

    DualRelay dual_relay;
    dual_relay_create(&dual_relay, "YOUR_DEVICE_UID", &ipcon);

 This device object can be used after the IP connection has been connected
 (see examples :ref:`above <dual_relay_bricklet_c_examples>`).

.. c:function:: void dual_relay_destroy(DualRelay *dual_relay)

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


.. c:function:: int dual_relay_set_state(DualRelay *dual_relay, bool relay1, bool relay2)

 Sets the state of the relays, *true* means on and *false* means off. 
 For example: (true, false) turns relay 1 on and relay 2 off.
 
 If you just want to set one of the relays and don't know the current state
 of the other relay, you can get the state with :c:func:`dual_relay_get_state` or you
 can use :c:func:`dual_relay_set_selected_state`.
 
 Running monoflop timers will be overwritten if this function is called.
 
 The default value is (*false*, *false*).
 
.. c:function:: int dual_relay_get_state(DualRelay *dual_relay, bool *ret_relay1, bool *ret_relay2)

 Returns the state of the relays, *true* means on and *false* means off. 
 


Advanced Functions
^^^^^^^^^^^^^^^^^^

.. c:function:: int dual_relay_set_monoflop(DualRelay *dual_relay, uint8_t relay, bool state, uint32_t time)

 The first parameter can be 1 or 2 (relay 1 or relay 2). The second parameter 
 is the desired state of the relay (*true* means on and *false* means off).
 The third parameter indicates the time (in ms) that the relay should hold 
 the state.
 
 If this function is called with the parameters (1, true, 1500):
 Relay 1 will turn on and in 1.5s it will turn off again.
 
 A monoflop can be used as a failsafe mechanism. For example: Lets assume you 
 have a RS485 bus and a Dual Relay Bricklet connected to one of the slave 
 stacks. You can now call this function every second, with a time parameter
 of two seconds. The relay will be on all the time. If now the RS485 
 connection is lost, the relay will turn off in at most two seconds.
 
.. c:function:: int dual_relay_get_monoflop(DualRelay *dual_relay, uint8_t relay, bool *ret_state, uint32_t *ret_time, uint32_t *ret_time_remaining)

 Returns (for the given relay) the current state and the time as set by 
 :c:func:`dual_relay_set_monoflop` as well as the remaining time until the state flips.
 
 If the timer is not running currently, the remaining time will be returned
 as 0.
 
.. c:function:: int dual_relay_set_selected_state(DualRelay *dual_relay, uint8_t relay, bool state)

 Sets the state of the selected relay (1 or 2), *true* means on and *false* means off. 
 
 The other relay remains untouched.
 
.. c:function:: int dual_relay_get_api_version(DualRelay *dual_relay, 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 dual_relay_get_response_expected(DualRelay *dual_relay, 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:`dual_relay_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:`dual_relay_set_response_expected`
 for the list of function ID defines available for this function.
 
.. c:function:: int dual_relay_set_response_expected(DualRelay *dual_relay, 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:
 
 * DUAL_RELAY_FUNCTION_SET_STATE = 1
 * DUAL_RELAY_FUNCTION_SET_MONOFLOP = 3
 * DUAL_RELAY_FUNCTION_SET_SELECTED_STATE = 6
 
.. c:function:: int dual_relay_set_response_expected_all(DualRelay *dual_relay, bool response_expected)

 Changes the response expected flag for all setter and callback configuration
 functions of this device at once.
 
.. c:function:: int dual_relay_get_identity(DualRelay *dual_relay, 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 dual_relay_register_callback(DualRelay *dual_relay, 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 <dual_relay_bricklet_c_callbacks>`.




.. _dual_relay_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:`dual_relay_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);
    }

    dual_relay_register_callback(&dual_relay, DUAL_RELAY_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:: DUAL_RELAY_CALLBACK_MONOFLOP_DONE

 .. code-block:: c

  void callback(uint8_t relay, bool state, void *user_data)


 This callback is triggered whenever a monoflop timer reaches 0. The 
 parameter contain the relay (1 or 2) and the current state of the relay 
 (the state after the monoflop).
 


.. _dual_relay_bricklet_c_constants:

Constants
^^^^^^^^^

.. c:var:: DUAL_RELAY_DEVICE_IDENTIFIER

 This constant is used to identify a Dual Relay Bricklet.

 The :c:func:`dual_relay_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.

