Based on kernel version 4.7.2. Page generated on 2016-08-22 22:45 EST.
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 9 transporting raw IR data between userspace and kernelspace. Fundamentally, 10 it is just a chardev (/dev/lircX, for X = 0, 1, 2, ...), with a number 11 of standard struct file_operations defined on it. With respect to 12 transporting raw IR data to and fro, the essential fops are read, write 13 and 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 33 exact format of the data depends on what modes a driver supports, and what 34 mode has been selected. lircd obtains supported modes and sets the active mode 35 via the ioctl interface, detailed at <xref linkend="lirc_ioctl"/>. The generally 36 preferred mode is LIRC_MODE_MODE2, in which packets containing an int value 37 describing 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 46 values. Pulses and spaces are only marked implicitly by their position. The 47 data must start and end with a pulse, therefore, the data must always include 48 an uneven number of samples. The write function must block until the data has 49 been transmitted by the hardware. If more data is provided than the hardware 50 can 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 58 definition of struct file_operations, leaving us with an unsigned int 59 for the ioctl command and an unsigned long for the arg. For the purposes 60 of ioctl portability across 32-bit and 64-bit, these values are capped 61 to their 32-bit sizes.</para> 62 63 <para>The following ioctls can be used to change specific hardware settings. 64 In general each driver should have a default set of settings. The driver 65 implementation is expected to re-apply the default settings when the device 66 is closed by user-space, so that every application opening the device can rely 67 on 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>
