77 lines
2.9 KiB
ReStructuredText
77 lines
2.9 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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======================================================
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Infrared remote control support in video4linux drivers
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======================================================
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Authors: Gerd Hoffmann, Mauro Carvalho Chehab
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Basics
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======
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Most analog and digital TV boards support remote controllers. Several of
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them have a microprocessor that receives the IR carriers, convert into
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pulse/space sequences and then to scan codes, returning such codes to
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userspace ("scancode mode"). Other boards return just the pulse/space
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sequences ("raw mode").
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The support for remote controller in scancode mode is provided by the
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standard Linux input layer. The support for raw mode is provided via LIRC.
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In order to check the support and test it, it is suggested to download
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the `v4l-utils <https://git.linuxtv.org/v4l-utils.git/>`_. It provides
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two tools to handle remote controllers:
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- ir-keytable: provides a way to query the remote controller, list the
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protocols it supports, enable in-kernel support for IR decoder or
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switch the protocol and to test the reception of scan codes;
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- ir-ctl: provide tools to handle remote controllers that support raw mode
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via LIRC interface.
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Usually, the remote controller module is auto-loaded when the TV card is
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detected. However, for a few devices, you need to manually load the
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ir-kbd-i2c module.
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How it works
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============
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The modules register the remote as keyboard within the linux input
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layer, i.e. you'll see the keys of the remote as normal key strokes
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(if CONFIG_INPUT_KEYBOARD is enabled).
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Using the event devices (CONFIG_INPUT_EVDEV) it is possible for
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applications to access the remote via /dev/input/event<n> devices.
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The udev/systemd will automatically create the devices. If you install
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the `v4l-utils <https://git.linuxtv.org/v4l-utils.git/>`_, it may also
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automatically load a different keytable than the default one. Please see
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`v4l-utils <https://git.linuxtv.org/v4l-utils.git/>`_ ir-keytable.1
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man page for details.
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The ir-keytable tool is nice for trouble shooting, i.e. to check
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whenever the input device is really present, which of the devices it
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is, check whenever pressing keys on the remote actually generates
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events and the like. You can also use any other input utility that changes
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the keymaps, like the input kbd utility.
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Using with lircd
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----------------
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The latest versions of the lircd daemon supports reading events from the
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linux input layer (via event device). It also supports receiving IR codes
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in lirc mode.
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Using without lircd
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-------------------
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Xorg recognizes several IR keycodes that have its numerical value lower
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than 247. With the advent of Wayland, the input driver got updated too,
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and should now accept all keycodes. Yet, you may want to just reassign
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the keycodes to something that your favorite media application likes.
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This can be done by setting
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`v4l-utils <https://git.linuxtv.org/v4l-utils.git/>`_ to load your own
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keytable in runtime. Please read ir-keytable.1 man page for details.
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