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.. -*- coding: utf-8; mode: rst -*-
.. _lirc_dev_intro:
************
Introduction
************
LIRC stands for Linux Infrared Remote Control. The LIRC device interface is
a bi-directional interface for transporting raw IR and decoded scancodes
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 and
decoded scancodes 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 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-scancode:
.. _lirc-scancode-flag-toggle:
.. _lirc-scancode-flag-repeat:
``LIRC_MODE_SCANCODE``
This mode is for both sending and receiving IR.
For transmitting (aka sending), create a ``struct lirc_scancode`` with
the desired scancode set in the ``scancode`` member, :c:type:`rc_proto`
set the IR protocol, and all other members set to 0. Write this struct to
the lirc device.
For receiving, you read ``struct lirc_scancode`` from the lirc device,
with ``scancode`` set to the received scancode and the IR protocol
:c:type:`rc_proto`. If the scancode maps to a valid key code, this is set
in the ``keycode`` field, else it is set to ``KEY_RESERVED``.
The ``flags`` can have ``LIRC_SCANCODE_FLAG_TOGGLE`` set if the toggle
bit is set in protocols that support it (e.g. rc-5 and rc-6), or
``LIRC_SCANCODE_FLAG_REPEAT`` for when a repeat is received for protocols
that support it (e.g. nec).
In the Sanyo and NEC protocol, if you hold a button on remote, rather than
repeating the entire scancode, the remote sends a shorter message with
no scancode, which just means button is held, a "repeat". When this is
received, the ``LIRC_SCANCODE_FLAG_REPEAT`` is set and the scancode and
keycode is repeated.
With nec, there is no way to distinguish "button hold" from "repeatedly
pressing the same button". The rc-5 and rc-6 protocols have a toggle bit.
When a button is released and pressed again, the toggle bit is inverted.
If the toggle bit is set, the ``LIRC_SCANCODE_FLAG_TOGGLE`` is set.
The ``timestamp`` field is filled with the time nanoseconds
(in ``CLOCK_MONOTONIC``) when the scancode was decoded.
.. _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-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.
**************************
Remote Controller protocol
**************************
An enum :c:type:`rc_proto` in the :ref:`lirc_header` lists all the
supported IR protocols:
.. kernel-doc:: include/uapi/linux/lirc.h
|
