1 .. SPDX-License-Identifier: GPL-2.0
2
3 ======================================================
4 Infrared remote control support in video4linux drivers
5 ======================================================
6
7 Authors: Gerd Hoffmann, Mauro Carvalho Chehab
8
9 Basics
10 ======
11
12 Most analog and digital TV boards support remote controllers. Several of
13 them have a microprocessor that receives the IR carriers, convert into
14 pulse/space sequences and then to scan codes, returning such codes to
15 userspace ("scancode mode"). Other boards return just the pulse/space
16 sequences ("raw mode").
17
18 The support for remote controller in scancode mode is provided by the
19 standard Linux input layer. The support for raw mode is provided via LIRC.
20
21 In order to check the support and test it, it is suggested to download
22 the `v4l-utils <https://git.linuxtv.org/v4l-utils.git/>`_. It provides
23 two tools to handle remote controllers:
24
25 - ir-keytable: provides a way to query the remote controller, list the
26 protocols it supports, enable in-kernel support for IR decoder or
27 switch the protocol and to test the reception of scan codes;
28
29 - ir-ctl: provide tools to handle remote controllers that support raw mode
30 via LIRC interface.
31
32 Usually, the remote controller module is auto-loaded when the TV card is
33 detected. However, for a few devices, you need to manually load the
34 ir-kbd-i2c module.
35
36 How it works
37 ============
38
39 The modules register the remote as keyboard within the linux input
40 layer, i.e. you'll see the keys of the remote as normal key strokes
41 (if CONFIG_INPUT_KEYBOARD is enabled).
42
43 Using the event devices (CONFIG_INPUT_EVDEV) it is possible for
44 applications to access the remote via /dev/input/event<n> devices.
45 The udev/systemd will automatically create the devices. If you install
46 the `v4l-utils <https://git.linuxtv.org/v4l-utils.git/>`_, it may also
47 automatically load a different keytable than the default one. Please see
48 `v4l-utils <https://git.linuxtv.org/v4l-utils.git/>`_ ir-keytable.1
49 man page for details.
50
51 The ir-keytable tool is nice for trouble shooting, i.e. to check
52 whenever the input device is really present, which of the devices it
53 is, check whenever pressing keys on the remote actually generates
54 events and the like. You can also use any other input utility that changes
55 the keymaps, like the input kbd utility.
56
57
58 Using with lircd
59 ----------------
60
61 The latest versions of the lircd daemon supports reading events from the
62 linux input layer (via event device). It also supports receiving IR codes
63 in lirc mode.
64
65
66 Using without lircd
67 -------------------
68
69 Xorg recognizes several IR keycodes that have its numerical value lower
70 than 247. With the advent of Wayland, the input driver got updated too,
71 and should now accept all keycodes. Yet, you may want to just reassign
72 the keycodes to something that your favorite media application likes.
73
74 This can be done by setting
75 `v4l-utils <https://git.linuxtv.org/v4l-utils.git/>`_ to load your own
76 keytable in runtime. Please read ir-keytable.1 man page for details.
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.