1.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-no-invariants-or-later
2.. c:namespace:: RC
3
4.. _lirc-write:
5
6************
7LIRC write()
8************
9
10Name
11====
12
13lirc-write - Write to a LIRC device
14
15Synopsis
16========
17
18.. code-block:: c
19
20    #include <unistd.h>
21
22.. c:function:: ssize_t write( int fd, void *buf, size_t count )
23
24Arguments
25=========
26
27``fd``
28    File descriptor returned by ``open()``.
29
30``buf``
31    Buffer with data to be written
32
33``count``
34    Number of bytes at the buffer
35
36Description
37===========
38
39:c:func:`write()` writes up to ``count`` bytes to the device
40referenced by the file descriptor ``fd`` from the buffer starting at
41``buf``.
42
43The exact format of the data depends on what mode a driver is in, use
44:ref:`lirc_get_features` to get the supported modes and use
45:ref:`lirc_set_send_mode` set the mode.
46
47When in :ref:`LIRC_MODE_PULSE <lirc-mode-PULSE>` mode, the data written to
48the chardev is a pulse/space sequence of integer values. Pulses and spaces
49are only marked implicitly by their position. The data must start and end
50with a pulse, therefore, the data must always include an uneven number of
51samples. The write function blocks until the data has been transmitted
52by the hardware. If more data is provided than the hardware can send, the
53driver returns ``EINVAL``.
54
55When in :ref:`LIRC_MODE_SCANCODE <lirc-mode-scancode>` mode, one
56``struct lirc_scancode`` must be written to the chardev at a time, else
57``EINVAL`` is returned. Set the desired scancode in the ``scancode`` member,
58and the :ref:`IR protocol <Remote_controllers_Protocols>` in the
59:c:type:`rc_proto`: member. All other members must be
60set to 0, else ``EINVAL`` is returned. If there is no protocol encoder
61for the protocol or the scancode is not valid for the specified protocol,
62``EINVAL`` is returned. The write function blocks until the scancode
63is transmitted by the hardware.
64
65Return Value
66============
67
68On success, the number of bytes written is returned. It is not an error if
69this number is smaller than the number of bytes requested, or the amount
70of data required for one frame.  On error, -1 is returned, and the ``errno``
71variable is set appropriately. The generic error codes are described at the
72:ref:`Generic Error Codes <gen-errors>` chapter.
73