1 .. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.
2
3 .. _lirc_dev_intro:
4
5 ************
6 Introduction
7 ************
8
9 LIRC stands for Linux Infrared Remote Control.
10 a bi-directional interface for transporting ra
11 data between userspace and kernelspace. Fundam
12 (/dev/lircX, for X = 0, 1, 2, ...), with a num
13 file_operations defined on it. With respect to
14 decoded scancodes to and fro, the essential fo
15
16 It is also possible to attach a BPF program to
17 raw IR into scancodes.
18
19 Example dmesg output upon a driver registering
20
21 .. code-block:: none
22
23 $ dmesg |grep lirc_dev
24 rc rc0: lirc_dev: driver mceusb registered
25
26 What you should see for a chardev:
27
28 .. code-block:: none
29
30 $ ls -l /dev/lirc*
31 crw-rw---- 1 root root 248, 0 Jul 2 22:20
32
33 Note that the package `v4l-utils <https://git.
34 contains tools for working with LIRC devices:
35
36 - ir-ctl: can receive raw IR and transmit IR,
37 device features.
38
39 - ir-keytable: can load keymaps; allows you t
40 BPF IR decoders and test IR decoding. Some
41 provided.
42
43 .. _lirc_modes:
44
45 **********
46 LIRC modes
47 **********
48
49 LIRC supports some modes of receiving and send
50 on the following table.
51
52 .. _lirc-mode-scancode:
53 .. _lirc-scancode-flag-toggle:
54 .. _lirc-scancode-flag-repeat:
55
56 ``LIRC_MODE_SCANCODE``
57
58 This mode is for both sending and receivin
59
60 For transmitting (aka sending), create a s
61 the desired scancode set in the ``scancode
62 set to the :ref:`IR protocol <Remote_contr
63 members set to 0. Write this struct to the
64
65 For receiving, you read struct lirc_scanco
66 The ``scancode`` field is set to the recei
67 :ref:`IR protocol <Remote_controllers_Prot
68 :c:type:`rc_proto`. If the scancode maps t
69 in the ``keycode`` field, else it is set t
70
71 The ``flags`` can have ``LIRC_SCANCODE_FLA
72 bit is set in protocols that support it (e
73 ``LIRC_SCANCODE_FLAG_REPEAT`` for when a r
74 that support it (e.g. nec).
75
76 In the Sanyo and NEC protocol, if you hold
77 repeating the entire scancode, the remote
78 no scancode, which just means button is he
79 received, the ``LIRC_SCANCODE_FLAG_REPEAT`
80 keycode is repeated.
81
82 With nec, there is no way to distinguish "
83 pressing the same button". The rc-5 and rc
84 When a button is released and pressed agai
85 If the toggle bit is set, the ``LIRC_SCANC
86
87 The ``timestamp`` field is filled with the
88 (in ``CLOCK_MONOTONIC``) when the scancode
89
90 .. _lirc-mode-mode2:
91
92 ``LIRC_MODE_MODE2``
93
94 The driver returns a sequence of pulse and
95 as a series of u32 values.
96
97 This mode is used only for IR receive.
98
99 The upper 8 bits determine the packet type
100 the payload. Use ``LIRC_VALUE()`` macro to
101 the macro ``LIRC_MODE2()`` will give you t
102 is one of:
103
104 ``LIRC_MODE2_PULSE``
105
106 Signifies the presence of IR in micros
107
108 ``LIRC_MODE2_SPACE``
109
110 Signifies absence of IR in microsecond
111
112 ``LIRC_MODE2_FREQUENCY``
113
114 If measurement of the carrier frequenc
115 :ref:`lirc_set_measure_carrier_mode` t
116 the carrier frequency in Hertz.
117
118 ``LIRC_MODE2_TIMEOUT``
119
120 When the timeout set with :ref:`lirc_s
121 to no IR being detected, this packet w
122 of microseconds with no IR.
123
124 ``LIRC_MODE2_OVERFLOW``
125
126 Signifies that the IR receiver encount
127 is missing. The IR data after this sho
128 actual value is not important, but thi
129 kernel for compatibility with lircd.
130
131 .. _lirc-mode-pulse:
132
133 ``LIRC_MODE_PULSE``
134
135 In pulse mode, a sequence of pulse/space i
136 lirc device using :ref:`lirc-write`.
137
138 The values are alternating pulse and space
139 first and last entry must be a pulse, so t
140 of entries.
141
142 This mode is used only for IR send.
143
144 *************************************
145 Data types used by LIRC_MODE_SCANCODE
146 *************************************
147
148 .. kernel-doc:: include/uapi/linux/lirc.h
149 :identifiers: lirc_scancode rc_proto
150
151 ********************
152 BPF based IR decoder
153 ********************
154
155 The kernel has support for decoding the most c
156 :ref:`IR protocols <Remote_controllers_Protoco
157 are many protocols which are not supported. To
158 to load an BPF program which does the decoding
159 LIRC devices which support reading raw IR.
160
161 First, using the `bpf(2)`_ syscall with the ``
162 program must be loaded of type ``BPF_PROG_TYPE
163 to the LIRC device, this program will be calle
164 timeout event on the LIRC device. The context
165 pointer to a unsigned int, which is a :ref:`LI
166 value. When the program has decoded the scanco
167 the BPF functions ``bpf_rc_keydown()`` or ``bp
168 movements can be reported using ``bpf_rc_point
169
170 Once you have the file descriptor for the ``BP
171 program, it can be attached to the LIRC device
172 The target must be the file descriptor for the
173 attach type must be ``BPF_LIRC_MODE2``. No mor
174 attached to a single LIRC device at a time.
175
176 .. _bpf(2): http://man7.org/linux/man-pages/ma
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