V4L/DVB: IR/lirc: add docbook info covering lirc device interface
First ever crack at creating docbook documentation... Contains a bevy of information on the various lirc device interface ioctls, as well as a bit about the read and write interfaces. Signed-off-by: Jarod Wilson <jarod@redhat.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
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Jarod Wilson
Mauro Carvalho Chehab
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Documentation/DocBook/v4l/lirc_device_interface.xml
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Documentation/DocBook/v4l/lirc_device_interface.xml
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<title>LIRC Device Interface</title>
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<section id="lirc_dev_intro">
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<title>Introduction</title>
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<para>The LIRC device interface is a bi-directional interface for
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transporting raw IR data between userspace and kernelspace. Fundamentally,
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it is just a chardev (/dev/lircX, for X = 0, 1, 2, ...), with a number
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of standard struct file_operations defined on it. With respect to
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transporting raw IR data to and fro, the essential fops are read, write
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and ioctl.</para>
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<para>Example dmesg output upon a driver registering w/LIRC:</para>
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<blockquote>
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<para>$ dmesg |grep lirc_dev</para>
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<para>lirc_dev: IR Remote Control driver registered, major 248</para>
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<para>rc rc0: lirc_dev: driver ir-lirc-codec (mceusb) registered at minor = 0</para>
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</blockquote>
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<para>
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<para>What you should see for a chardev:</para>
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<blockquote>
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<para>$ ls -l /dev/lirc*</para>
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<para>crw-rw---- 1 root root 248, 0 Jul 2 22:20 /dev/lirc0</para>
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</blockquote>
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</para>
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<section id="lirc_read">
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<title>LIRC read fop</title>
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<para>The lircd userspace daemon reads raw IR data from the LIRC chardev. The
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exact format of the data depends on what modes a driver supports, and what
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mode has been selected. lircd obtains supported modes and sets the active mode
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via the ioctl interface, detailed at <xref linkend="lirc_ioctl">. The generally
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preferred mode is LIRC_MODE_MODE2, in which packets containing an int value
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describing an IR signal are read from the chardev.</para>
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<para>See also <ulink url="http://www.lirc.org/html/technical.html">http://www.lirc.org/html/technical.html</> for more info.</para>
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<section id="lirc_write">
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<title>LIRC write fop</title>
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<para>The data written to the chardev is a pulse/space sequence of integer
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values. Pulses and spaces are only marked implicitly by their position. The
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data must start and end with a pulse, therefore, the data must always include
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an unevent number of samples. The write function must block until the data has
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been transmitted by the hardware.</para>
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<section id="lirc_ioctl">
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<title> LIRC ioctl fop</title>
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<para>The LIRC device's ioctl definition is bound by the ioctl function
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definition of struct file_operations, leaving us with an unsigned int
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for the ioctl command and an unsigned long for the arg. For the purposes
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of ioctl portability across 32-bit and 64-bit, these values are capped
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to their 32-bit sizes.</para>
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<para>The following ioctls can be used to change specific hardware settings.
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In general each driver should have a default set of settings. The driver
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implementation is expected to re-apply the default settings when the device
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is closed by user-space, so that every application opening the device can rely
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on working with the default settings initially.</para>
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<variablelist>
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<varlistentry>
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<term>LIRC_GET_FEATURES</term>
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<listitem>
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<to>Obviously, get the underlying hardware device's features. If a driver
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does not announce support of certain features, calling of the corresponding
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ioctls is undefined.</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_GET_SEND_MODE</term>
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<listitem>
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<to>Get supported transmit mode. Only LIRC_MODE_PULSE is supported by lircd.</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_GET_REC_MODE</term>
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<listitem>
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<to>Get supported receive modes. Only LIRC_MODE_MODE2 and LIRC_MODE_LIRCCODE
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are supported by lircd.</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_GET_SEND_CARRIER</term>
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<listitem>
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<to>Get carrier frequency (in Hz) currently used for transmit.</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_GET_REC_CARRIER</term>
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<listitem>
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<to>Get carrier frequency (in Hz) currently used for IR reception.</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_{G,S}ET_{SEND,REC}_DUTY_CYCLE</term>
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<listitem>
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<to>Get/set the duty cycle (from 0 to 100) of the carrier signal. Currently,
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no special meaning is defined for 0 or 100, but this could be used to switch
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off carrier generation in the future, so these values should be reserved.</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_GET_REC_RESOLUTION</term>
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<listitem>
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<to>Some receiver have maximum resolution which is defined by internal
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sample rate or data format limitations. E.g. it's common that signals can
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only be reported in 50 microsecond steps. This integer value is used by
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lircd to automatically adjust the aeps tolerance value in the lircd
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config file.</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_GET_M{IN,AX}_TIMEOUT</term>
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<listitem>
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<to>Some devices have internal timers that can be used to detect when
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there's no IR activity for a long time. This can help lircd in detecting
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that a IR signal is finished and can speed up the decoding process.
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Returns an integer value with the minimum/maximum timeout that can be
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set. Some devices have a fixed timeout, in that case both ioctls will
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return the same value even though the timeout cannot be changed.</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_GET_M{IN,AX}_FILTER_{PULSE,SPACE}</term>
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<listitem>
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<to>Some devices are able to filter out spikes in the incoming signal
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using given filter rules. These ioctls return the hardware capabilities
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that describe the bounds of the possible filters. Filter settings depend
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on the IR protocols that are expected. lircd derives the settings from
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all protocols definitions found in its config file.</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_GET_LENGTH</term>
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<listitem>
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<to>Retrieves the code length in bits (only for LIRC_MODE_LIRCCODE).
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Reads on the device must be done in blocks matching the bit count.
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The bit could should be rounded up so that it matches full bytes.</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_SET_{SEND,REC}_MODE</term>
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<listitem>
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<to>Set send/receive mode. Largely obsolete for send, as only
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LIRC_MODE_PULSE is supported.</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_SET_{SEND,REC}_CARRIER</term>
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<listitem>
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<to>Set send/receive carrier (in Hz).</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_SET_TRANSMITTER_MASK</term>
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<listitem>
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<to>This enables the given set of transmitters. The first transmitter
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is encoded by the least significant bit, etc. When an invalid bit mask
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is given, i.e. a bit is set, even though the device does not have so many
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transitters, then this ioctl returns the number of available transitters
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and does nothing otherwise.</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_SET_REC_TIMEOUT</term>
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<listitem>
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<to>Sets the integer value for IR inactivity timeout (cf.
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LIRC_GET_MIN_TIMEOUT and LIRC_GET_MAX_TIMEOUT). A value of 0 (if
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supported by the hardware) disables all hardware timeouts and data should
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be reported as soon as possible. If the exact value cannot be set, then
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the next possible value _greater_ than the given value should be set.</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_SET_REC_TIMEOUT_REPORTS</term>
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<listitem>
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<to>Enable (1) or disable (0) timeout reports in LIRC_MODE_MODE2. By
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default, timeout reports should be turned off.</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_SET_REC_FILTER_{,PULSE,SPACE}</term>
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<listitem>
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<to>Pulses/spaces shorter than this are filtered out by hardware. If
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filters cannot be set independently for pulse/space, the corresponding
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ioctls must return an error and LIRC_SET_REC_FILTER shall be used instead.</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_SET_MEASURE_CARRIER_MODE</term>
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<listitem>
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<to>Enable (1)/disable (0) measure mode. If enabled, from the next key
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press on, the driver will send LIRC_MODE2_FREQUENCY packets. By default
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this should be turned off.</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_SET_REC_{DUTY_CYCLE,CARRIER}_RANGE</term>
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<listitem>
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<to>To set a range use LIRC_SET_REC_DUTY_CYCLE_RANGE/LIRC_SET_REC_CARRIER_RANGE
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with the lower bound first and later LIRC_SET_REC_DUTY_CYCLE/LIRC_SET_REC_CARRIER
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with the upper bound.</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_NOTIFY_DECODE</term>
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<listitem>
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<to>This ioctl is called by lircd whenever a successful decoding of an
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incoming IR signal could be done. This can be used by supporting hardware
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to give visual feedback to the user e.g. by flashing a LED.</to>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LIRC_SETUP_{START,END}</term>
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<listitem>
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<to>Setting of several driver parameters can be optimized by encapsulating
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the according ioctl calls with LIRC_SETUP_START/LIRC_SETUP_END. When a
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driver receives a LIRC_SETUP_START ioctl it can choose to not commit
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further setting changes to the hardware until a LIRC_SETUP_END is received.
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But this is open to the driver implementation and every driver must also
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handle parameter changes which are not encapsulated by LIRC_SETUP_START
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and LIRC_SETUP_END. Drivers can also choose to ignore these ioctls.</to>
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</listitem>
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</varlistentry>
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</variablelist>
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</section>
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