Documentation/media/uapi/rc/lirc-dev-intro.rst

.. -*- coding: utf-8; mode: rst -*-

.. _lirc_dev_intro:

************
Introduction
************

The LIRC device interface is a bi-directional interface for transporting
raw IR data between userspace and kernelspace. Fundamentally, it is just
a chardev (/dev/lircX, for X = 0, 1, 2, ...), with a number of standard
struct file_operations defined on it. With respect to transporting raw
IR data to and fro, the essential fops are read, write and ioctl.

Example dmesg output upon a driver registering w/LIRC:

.. code-block:: none

    $ dmesg |grep lirc_dev
    lirc_dev: IR Remote Control driver registered, major 248
    rc rc0: lirc_dev: driver ir-lirc-codec (mceusb) registered at minor = 0

What you should see for a chardev:

.. code-block:: none

    $ ls -l /dev/lirc*
    crw-rw---- 1 root root 248, 0 Jul 2 22:20 /dev/lirc0

.. _lirc_modes:

**********
LIRC modes
**********

LIRC supports some modes of receiving and sending IR codes, as shown
on the following table.

.. _lirc-mode-mode2:

``LIRC_MODE_MODE2``

    The driver returns a sequence of pulse and space codes to userspace,
    as a series of u32 values.

    This mode is used only for IR receive.

    The upper 8 bits determine the packet type, and the lower 24 bits
    the payload. Use ``LIRC_VALUE()`` macro to get the payload, and
    the macro ``LIRC_MODE2()`` will give you the type, which
    is one of:

    ``LIRC_MODE2_PULSE``

        Signifies the presence of IR in microseconds.

    ``LIRC_MODE2_SPACE``

        Signifies absence of IR in microseconds.

    ``LIRC_MODE2_FREQUENCY``

        If measurement of the carrier frequency was enabled with
        :ref:`lirc_set_measure_carrier_mode` then this packet gives you
        the carrier frequency in Hertz.

    ``LIRC_MODE2_TIMEOUT``

        If timeout reports are enabled with
        :ref:`lirc_set_rec_timeout_reports`, when the timeout set with
        :ref:`lirc_set_rec_timeout` expires due to no IR being detected,
        this packet will be sent, with the number of microseconds with
        no IR.

.. _lirc-mode-lirccode:

``LIRC_MODE_LIRCCODE``

    This mode can be used for IR receive and send.

    The IR signal is decoded internally by the receiver, or encoded by the
    transmitter. The LIRC interface represents the scancode as byte string,
    which might not be a u32, it can be any length. The value is entirely
    driver dependent. This mode is used by some older lirc drivers.

    The length of each code depends on the driver, which can be retrieved
    with :ref:`lirc_get_length`. This length is used both
    for transmitting and receiving IR.

.. _lirc-mode-pulse:

``LIRC_MODE_PULSE``

    In pulse mode, a sequence of pulse/space integer values are written to the
    lirc device using :ref:`lirc-write`.

    The values are alternating pulse and space lengths, in microseconds. The
    first and last entry must be a pulse, so there must be an odd number
    of entries.

    This mode is used only for IR send.