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