1<section id="lirc_dev">
2<title>LIRC Device Interface</title>
3
4
5<section id="lirc_dev_intro">
6<title>Introduction</title>
7
8<para>The LIRC device interface is a bi-directional interface for
9transporting raw IR data between userspace and kernelspace. Fundamentally,
10it is just a chardev (/dev/lircX, for X = 0, 1, 2, ...), with a number
11of standard struct file_operations defined on it. With respect to
12transporting raw IR data to and fro, the essential fops are read, write
13and ioctl.</para>
14
15<para>Example dmesg output upon a driver registering w/LIRC:</para>
16  <blockquote>
17    <para>$ dmesg |grep lirc_dev</para>
18    <para>lirc_dev: IR Remote Control driver registered, major 248</para>
19    <para>rc rc0: lirc_dev: driver ir-lirc-codec (mceusb) registered at minor = 0</para>
20  </blockquote>
21
22<para>What you should see for a chardev:</para>
23  <blockquote>
24    <para>$ ls -l /dev/lirc*</para>
25    <para>crw-rw---- 1 root root 248, 0 Jul  2 22:20 /dev/lirc0</para>
26  </blockquote>
27</section>
28
29<section id="lirc_read">
30<title>LIRC read fop</title>
31
32<para>The lircd userspace daemon reads raw IR data from the LIRC chardev. The
33exact format of the data depends on what modes a driver supports, and what
34mode has been selected. lircd obtains supported modes and sets the active mode
35via the ioctl interface, detailed at <xref linkend="lirc_ioctl"/>. The generally
36preferred mode is LIRC_MODE_MODE2, in which packets containing an int value
37describing an IR signal are read from the chardev.</para>
38
39<para>See also <ulink url="http://www.lirc.org/html/technical.html">http://www.lirc.org/html/technical.html</ulink> for more info.</para>
40</section>
41
42<section id="lirc_write">
43<title>LIRC write fop</title>
44
45<para>The data written to the chardev is a pulse/space sequence of integer
46values. Pulses and spaces are only marked implicitly by their position. The
47data must start and end with a pulse, therefore, the data must always include
48an uneven number of samples. The write function must block until the data has
49been transmitted by the hardware. If more data is provided than the hardware
50can send, the driver returns EINVAL.</para>
51
52</section>
53
54<section id="lirc_ioctl">
55<title>LIRC ioctl fop</title>
56
57<para>The LIRC device's ioctl definition is bound by the ioctl function
58definition of struct file_operations, leaving us with an unsigned int
59for the ioctl command and an unsigned long for the arg. For the purposes
60of ioctl portability across 32-bit and 64-bit, these values are capped
61to their 32-bit sizes.</para>
62
63<para>The following ioctls can be used to change specific hardware settings.
64In general each driver should have a default set of settings. The driver
65implementation is expected to re-apply the default settings when the device
66is closed by user-space, so that every application opening the device can rely
67on working with the default settings initially.</para>
68
69<variablelist>
70  <varlistentry>
71    <term>LIRC_GET_FEATURES</term>
72    <listitem>
73      <para>Obviously, get the underlying hardware device's features. If a driver
74      does not announce support of certain features, calling of the corresponding
75      ioctls is undefined.</para>
76    </listitem>
77  </varlistentry>
78  <varlistentry>
79    <term>LIRC_GET_SEND_MODE</term>
80    <listitem>
81      <para>Get supported transmit mode. Only LIRC_MODE_PULSE is supported by lircd.</para>
82    </listitem>
83  </varlistentry>
84  <varlistentry>
85    <term>LIRC_GET_REC_MODE</term>
86    <listitem>
87      <para>Get supported receive modes. Only LIRC_MODE_MODE2 and LIRC_MODE_LIRCCODE
88      are supported by lircd.</para>
89    </listitem>
90  </varlistentry>
91  <varlistentry>
92    <term>LIRC_GET_SEND_CARRIER</term>
93    <listitem>
94      <para>Get carrier frequency (in Hz) currently used for transmit.</para>
95    </listitem>
96  </varlistentry>
97  <varlistentry>
98    <term>LIRC_GET_REC_CARRIER</term>
99    <listitem>
100      <para>Get carrier frequency (in Hz) currently used for IR reception.</para>
101    </listitem>
102  </varlistentry>
103  <varlistentry>
104    <term>LIRC_{G,S}ET_{SEND,REC}_DUTY_CYCLE</term>
105    <listitem>
106      <para>Get/set the duty cycle (from 0 to 100) of the carrier signal. Currently,
107      no special meaning is defined for 0 or 100, but this could be used to switch
108      off carrier generation in the future, so these values should be reserved.</para>
109    </listitem>
110  </varlistentry>
111  <varlistentry>
112    <term>LIRC_GET_REC_RESOLUTION</term>
113    <listitem>
114      <para>Some receiver have maximum resolution which is defined by internal
115      sample rate or data format limitations. E.g. it's common that signals can
116      only be reported in 50 microsecond steps. This integer value is used by
117      lircd to automatically adjust the aeps tolerance value in the lircd
118      config file.</para>
119    </listitem>
120  </varlistentry>
121  <varlistentry>
122    <term>LIRC_GET_M{IN,AX}_TIMEOUT</term>
123    <listitem>
124      <para>Some devices have internal timers that can be used to detect when
125      there's no IR activity for a long time. This can help lircd in detecting
126      that a IR signal is finished and can speed up the decoding process.
127      Returns an integer value with the minimum/maximum timeout that can be
128      set. Some devices have a fixed timeout, in that case both ioctls will
129      return the same value even though the timeout cannot be changed.</para>
130    </listitem>
131  </varlistentry>
132  <varlistentry>
133    <term>LIRC_GET_M{IN,AX}_FILTER_{PULSE,SPACE}</term>
134    <listitem>
135      <para>Some devices are able to filter out spikes in the incoming signal
136      using given filter rules. These ioctls return the hardware capabilities
137      that describe the bounds of the possible filters. Filter settings depend
138      on the IR protocols that are expected. lircd derives the settings from
139      all protocols definitions found in its config file.</para>
140    </listitem>
141  </varlistentry>
142  <varlistentry>
143    <term>LIRC_GET_LENGTH</term>
144    <listitem>
145      <para>Retrieves the code length in bits (only for LIRC_MODE_LIRCCODE).
146      Reads on the device must be done in blocks matching the bit count.
147      The bit could should be rounded up so that it matches full bytes.</para>
148    </listitem>
149  </varlistentry>
150  <varlistentry>
151    <term>LIRC_SET_{SEND,REC}_MODE</term>
152    <listitem>
153      <para>Set send/receive mode. Largely obsolete for send, as only
154      LIRC_MODE_PULSE is supported.</para>
155    </listitem>
156  </varlistentry>
157  <varlistentry>
158    <term>LIRC_SET_{SEND,REC}_CARRIER</term>
159    <listitem>
160      <para>Set send/receive carrier (in Hz).</para>
161    </listitem>
162  </varlistentry>
163  <varlistentry>
164    <term>LIRC_SET_TRANSMITTER_MASK</term>
165    <listitem>
166      <para>This enables the given set of transmitters. The first transmitter
167      is encoded by the least significant bit, etc. When an invalid bit mask
168      is given, i.e. a bit is set, even though the device does not have so many
169      transitters, then this ioctl returns the number of available transitters
170      and does nothing otherwise.</para>
171    </listitem>
172  </varlistentry>
173  <varlistentry>
174    <term>LIRC_SET_REC_TIMEOUT</term>
175    <listitem>
176      <para>Sets the integer value for IR inactivity timeout (cf.
177      LIRC_GET_MIN_TIMEOUT and LIRC_GET_MAX_TIMEOUT). A value of 0 (if
178      supported by the hardware) disables all hardware timeouts and data should
179      be reported as soon as possible. If the exact value cannot be set, then
180      the next possible value _greater_ than the given value should be set.</para>
181    </listitem>
182  </varlistentry>
183  <varlistentry>
184    <term>LIRC_SET_REC_TIMEOUT_REPORTS</term>
185    <listitem>
186      <para>Enable (1) or disable (0) timeout reports in LIRC_MODE_MODE2. By
187      default, timeout reports should be turned off.</para>
188    </listitem>
189  </varlistentry>
190  <varlistentry>
191    <term>LIRC_SET_REC_FILTER_{,PULSE,SPACE}</term>
192    <listitem>
193      <para>Pulses/spaces shorter than this are filtered out by hardware. If
194      filters cannot be set independently for pulse/space, the corresponding
195      ioctls must return an error and LIRC_SET_REC_FILTER shall be used instead.</para>
196    </listitem>
197  </varlistentry>
198  <varlistentry>
199    <term>LIRC_SET_MEASURE_CARRIER_MODE</term>
200    <listitem>
201      <para>Enable (1)/disable (0) measure mode. If enabled, from the next key
202      press on, the driver will send LIRC_MODE2_FREQUENCY packets. By default
203      this should be turned off.</para>
204    </listitem>
205  </varlistentry>
206  <varlistentry>
207    <term>LIRC_SET_REC_{DUTY_CYCLE,CARRIER}_RANGE</term>
208    <listitem>
209      <para>To set a range use LIRC_SET_REC_DUTY_CYCLE_RANGE/LIRC_SET_REC_CARRIER_RANGE
210      with the lower bound first and later LIRC_SET_REC_DUTY_CYCLE/LIRC_SET_REC_CARRIER
211      with the upper bound.</para>
212    </listitem>
213  </varlistentry>
214  <varlistentry>
215    <term>LIRC_NOTIFY_DECODE</term>
216    <listitem>
217      <para>This ioctl is called by lircd whenever a successful decoding of an
218      incoming IR signal could be done. This can be used by supporting hardware
219      to give visual feedback to the user e.g. by flashing a LED.</para>
220    </listitem>
221  </varlistentry>
222  <varlistentry>
223    <term>LIRC_SETUP_{START,END}</term>
224    <listitem>
225      <para>Setting of several driver parameters can be optimized by encapsulating
226      the according ioctl calls with LIRC_SETUP_START/LIRC_SETUP_END. When a
227      driver receives a LIRC_SETUP_START ioctl it can choose to not commit
228      further setting changes to the hardware until a LIRC_SETUP_END is received.
229      But this is open to the driver implementation and every driver must also
230      handle parameter changes which are not encapsulated by LIRC_SETUP_START
231      and LIRC_SETUP_END. Drivers can also choose to ignore these ioctls.</para>
232    </listitem>
233  </varlistentry>
234  <varlistentry>
235    <term>LIRC_SET_WIDEBAND_RECEIVER</term>
236    <listitem>
237      <para>Some receivers are equipped with special wide band receiver which is intended
238      to be used to learn output of existing remote.
239      Calling that ioctl with (1) will enable it, and with (0) disable it.
240      This might be useful of receivers that have otherwise narrow band receiver
241      that prevents them to be used with some remotes.
242      Wide band receiver might also be more precise
243      On the other hand its disadvantage it usually reduced range of reception.
244      Note: wide band receiver might be implictly enabled if you enable
245      carrier reports. In that case it will be disabled as soon as you disable
246      carrier reports. Trying to disable wide band receiver while carrier
247      reports are active will do nothing.</para>
248    </listitem>
249  </varlistentry>
250</variablelist>
251<section id="lirc_dev_errors">
252  &return-value;
253</section>
254</section>
255</section>
256