134 lines
4.3 KiB
ReStructuredText
134 lines
4.3 KiB
ReStructuredText
.. -*- coding: utf-8; mode: rst -*-
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.. _lirc_dev_intro:
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************
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Introduction
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************
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LIRC stands for Linux Infrared Remote Control. The LIRC device interface is
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a bi-directional interface for transporting raw IR and decoded scancodes
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data between userspace and kernelspace. Fundamentally, it is just a chardev
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(/dev/lircX, for X = 0, 1, 2, ...), with a number of standard struct
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file_operations defined on it. With respect to transporting raw IR and
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decoded scancodes to and fro, the essential fops are read, write and ioctl.
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Example dmesg output upon a driver registering w/LIRC:
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.. code-block:: none
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$ dmesg |grep lirc_dev
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rc rc0: lirc_dev: driver mceusb registered at minor = 0, raw IR receiver, raw IR transmitter
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What you should see for a chardev:
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.. code-block:: none
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$ ls -l /dev/lirc*
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crw-rw---- 1 root root 248, 0 Jul 2 22:20 /dev/lirc0
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.. _lirc_modes:
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**********
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LIRC modes
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**********
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LIRC supports some modes of receiving and sending IR codes, as shown
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on the following table.
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.. _lirc-mode-scancode:
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.. _lirc-scancode-flag-toggle:
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.. _lirc-scancode-flag-repeat:
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``LIRC_MODE_SCANCODE``
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This mode is for both sending and receiving IR.
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For transmitting (aka sending), create a ``struct lirc_scancode`` with
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the desired scancode set in the ``scancode`` member, :c:type:`rc_proto`
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set the IR protocol, and all other members set to 0. Write this struct to
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the lirc device.
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For receiving, you read ``struct lirc_scancode`` from the lirc device,
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with ``scancode`` set to the received scancode and the IR protocol
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:c:type:`rc_proto`. If the scancode maps to a valid key code, this is set
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in the ``keycode`` field, else it is set to ``KEY_RESERVED``.
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The ``flags`` can have ``LIRC_SCANCODE_FLAG_TOGGLE`` set if the toggle
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bit is set in protocols that support it (e.g. rc-5 and rc-6), or
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``LIRC_SCANCODE_FLAG_REPEAT`` for when a repeat is received for protocols
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that support it (e.g. nec).
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In the Sanyo and NEC protocol, if you hold a button on remote, rather than
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repeating the entire scancode, the remote sends a shorter message with
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no scancode, which just means button is held, a "repeat". When this is
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received, the ``LIRC_SCANCODE_FLAG_REPEAT`` is set and the scancode and
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keycode is repeated.
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With nec, there is no way to distinguish "button hold" from "repeatedly
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pressing the same button". The rc-5 and rc-6 protocols have a toggle bit.
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When a button is released and pressed again, the toggle bit is inverted.
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If the toggle bit is set, the ``LIRC_SCANCODE_FLAG_TOGGLE`` is set.
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The ``timestamp`` field is filled with the time nanoseconds
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(in ``CLOCK_MONOTONIC``) when the scancode was decoded.
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.. _lirc-mode-mode2:
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``LIRC_MODE_MODE2``
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The driver returns a sequence of pulse and space codes to userspace,
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as a series of u32 values.
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This mode is used only for IR receive.
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The upper 8 bits determine the packet type, and the lower 24 bits
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the payload. Use ``LIRC_VALUE()`` macro to get the payload, and
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the macro ``LIRC_MODE2()`` will give you the type, which
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is one of:
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``LIRC_MODE2_PULSE``
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Signifies the presence of IR in microseconds.
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``LIRC_MODE2_SPACE``
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Signifies absence of IR in microseconds.
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``LIRC_MODE2_FREQUENCY``
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If measurement of the carrier frequency was enabled with
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:ref:`lirc_set_measure_carrier_mode` then this packet gives you
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the carrier frequency in Hertz.
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``LIRC_MODE2_TIMEOUT``
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If timeout reports are enabled with
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:ref:`lirc_set_rec_timeout_reports`, when the timeout set with
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:ref:`lirc_set_rec_timeout` expires due to no IR being detected,
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this packet will be sent, with the number of microseconds with
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no IR.
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.. _lirc-mode-pulse:
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``LIRC_MODE_PULSE``
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In pulse mode, a sequence of pulse/space integer values are written to the
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lirc device using :ref:`lirc-write`.
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The values are alternating pulse and space lengths, in microseconds. The
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first and last entry must be a pulse, so there must be an odd number
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of entries.
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This mode is used only for IR send.
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**************************
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Remote Controller protocol
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**************************
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An enum :c:type:`rc_proto` in the :ref:`lirc_header` lists all the
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supported IR protocols:
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.. kernel-doc:: include/uapi/linux/lirc.h
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