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