mirror of https://github.com/mkerrisk/man-pages
lirc.3: Document lirc device driver
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.TH LIRC 4 "Aug 2015" "Linux" "Linux Programmer's Manual"
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.\" Copyright (c) 2015, Alec Leamas
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.\"
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.\" %%%LICENSE_START(GPLv2+_DOC_FULL)
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.\" This is free documentation; you can redistribute it and/or
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.\" modify it under the terms of the GNU General Public License as
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.\" published by the Free Software Foundation; either version 2 of
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.\" the License, or (at your option) any later version.
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.\"
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.\" The GNU General Public License's references to "object code"
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.\" and "executables" are to be interpreted as the output of any
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.\" document formatting or typesetting system, including
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.\" intermediate and printed output.
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.\"
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.\" This manual is distributed in the hope that it will be useful,
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.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
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.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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.\" GNU General Public License for more details.
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.\"
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.\" You should have received a copy of the GNU General Public
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.\" License along with this manual; if not, see
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.\" <http://www.gnu.org/licenses/>.
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.\" %%%LICENSE_END
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.SH NAME
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lirc \- lirc devices
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.SH DESCRIPTION
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.P
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\fB/dev/lirc*\fR are character devices providing a low-level
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bi-directional interface to infra-red (IR) remotes.
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When receiving data, the driver works in two different modes depending
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on the underlying hardware.
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.P
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Some hardware (typically TV-cards) decodes the IR signal internally
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and just provides decoded button presses as integer values.
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Drivers for this kind of hardware work in
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.BR LIRC_MODE_LIRCCODE .
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Such hardware usually does not support sending IR signals.
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Furthermore, it usually only works with a specific remote which is
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bundled with, for example, a TV-card.
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.P
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Other hardware provides a stream of pulse/space durations.
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Such drivers work in
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.BR LIRC_MODE_MODE2 .
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Sometimes, this kind of hardware also supports
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sending IR data.
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Such hardware can be used with (almost) any kind of remote.
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.P
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The \fBLIRC_GET_REC_MODE\fR ioctl (see below) allows probing for the
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mode.
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.SS Reading input with the LIRC_MODE_MODE2 drivers
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.P
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In the \fBLIRC_MODE_MODE2 mode\fR, the data returned by
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.BR read (2)
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provides 32-bit values representing a space or a pulse duration, by
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convention typed as
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.IR lirc_t .
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The time of the duration (microseonds) is encoded in the lower 24 bits.
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The upper 8 bit reflects the type of package:
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.TP 4
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.BR LIRC_MODE2_SPACE .
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Value reflects a space duration (microseconds).
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.TP 4
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.BR LIRC_MODE2_PULSE .
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Value reflects a pulse duration (microseconds).
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.TP 4
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.BR LIRC_MODE2_FREQUENCY .
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Value reflects a frequency (hz), see the
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.B LIRC_SET_MEASURE_CARRIER
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ioctl.
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.TP 4
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.BR LIRC_MODE2_TIMEOUT .
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The package reflects a timeout, see the
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.B LIRC_SET_REC_TIMEOUT_REPORTS
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ioctl.
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.SS Reading input with the
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.B LIRC_MODE_LIRCCODE
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drivers
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.P
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In the \fBLIRC_MODE_LIRCCODE\fR
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mode, the data returned by
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.BR read2()
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reflects decoded button presses.
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The length of each packet can be retrieved using
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the \fBLIRC_GET_LENGTH\fR ioctl.
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Reads must be done in blocks matching
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the bit count returned by the \fBLIRC_GET_LENGTH\fR ioctl, rounded
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up so it matches full bytes.
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.SS Sending data
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.P
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When sending data, only the \fBLIRC_MODE_PULSE\fR
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mode is supported.
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The data written to the character device using
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.BR write(2)
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is a pulse/space sequence of integer values.
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Pulses and spaces are only marked implicitly by their position.
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The data must start and end with a pulse, thus it must always include
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an odd number of samples.
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The
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.BR write(2)
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function blocks until the data has been transmitted by the
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hardware.
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If more data is provided than the hardware can send, the
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.BR write(2)
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call fails with the error
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.BR EINVAL
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.SH SUPPORTED IOCTL COMMANDS
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.P
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.nf
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#include " (\fIlirc/include/media/lirc.h\fP) " /* But see BUGS */
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int ioctl(int fd, int cmd, ...);
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.fi
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.P
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The following ioctls can be used to probe or change specific lirc
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hardware settings.
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Many require a third argument, usually an
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.IR int .
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referred to below as
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.I val .
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.P
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In general, each driver should have a default set of settings.
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The driver implementation is expected to re-apply the default settings
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when the device is closed by userspace, so that every application
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opening the device can rely on working with the default settings
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initially.
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.BR
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.SS Always Supported Commands
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.P
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\fI/dev/lirc*\fR devices always support the following commands:
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.TP 4
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.BR LIRC_GET_FEATURES " (\fIvoid\fP)"
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Returns a bitmask of combined features bits, see FEATURES.
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Some drivers have dynamic features which are not updated until after
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an init() command.
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.TP
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.BR LIRC_GET_REC_MODE ,
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Returns the receive mode, which will be one of:
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.RS 4
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.TP
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.BR LIRC_MODE_MODE2 " (\fIvoid\fP)"
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Driver returns a sequence of pulse/space durations.
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.TP
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.BR LIRC_MODE_LIRCCODE
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Driver returns integer values, each of which represents a decoded
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button press.
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.RE
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.P
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If a device returns an error code for
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.BR LIRC_GET_REC_MODE
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it is safe to assume it is not a lirc device.
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.SS Optional Commands
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.P
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Some lirc devices support commands listed below.
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Unless otherwise stated, these fail with the error \fBENOIOCTLCMD\fR
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or with the error \fBENOSYS\fR if the operation
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isn't supported, or with the error \fBEINVAL\fR if the operation
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failed.
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.TP
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.BR LIRC_SET_REC_MODE " (\fIint\fP)"
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Set the receive mode.
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.IR val
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is either
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.BR LIRC_MODE_LIRCCODE
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or
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.BR LIRC_MODE_MODE2 .
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.TP
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.BR LIRC_GET_LENGTH " (\fIvoid\fP)"
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Return the length of the returned codes for
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.BR LIRC_LIRCCODE
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type
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drivers, otherwise fail with the error
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.BR ENOIOCTLCMD .
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.TP
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.BR LIRC_GET_SEND_MODE " (\fIvoid\fP)"
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Returns the send mode; currently only
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.BR LIRC_MODE_PULSE
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is supported.
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.TP
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.BR LIRC_SET_SEND_MODE " (\fIint\fP)"
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Set the send mode.
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Currently serves no purpose since only
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.BR LIRC_MODE_PULSE
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is supported.
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.TP
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.BR LIRC_SET_SEND_CARRIER " (\fIint\fP)"
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Set the modulation frequency. The argument is the frequency (Hz).
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.TP
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.BR SET_SEND_DUTY_CYCLE " (\fIint\fP)"
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Set the carrier duty cycle.
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The argument is an int (0 < value < 100) which
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describes the pulse width in percent of the total cycle.
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Currently, no special meaning is defined for 0 or 100, but the values
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are reserved for future use.
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.TP
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.BR LIRC_GET_MIN_TIMEOUT " (\fIvoid\fP)", " "\
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LIRC_GET_MAX_TIMEOUT " (\fIvoid\fP)"
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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.
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This can help
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.BR lircd(8)
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in detecting that an IR signal is finished and can speed up the
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decoding process.
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Returns an integer value with the minimum/maximum timeout that can be
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set (microseconds).
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Some devices have a fixed timeout. For such drivers,
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.BR LIRC_GET_MIN_TIMEOUT
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and
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.BR LIRC_GET_MAX_TIMEOUT
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will return the same value.
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.TP
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.BR LIRC_SET_REC_TIMEOUT " (\fIint\fP)"
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Sets the integer value for IR inactivity timeout (microseconds).
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To be accepted, the value must be within the limits defined by
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.BR LIRC_GET_MIN_TIMEOUT
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and
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.BR LIRC_GET_MAX_TIMEOUT .
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A value of 0 (if supported by the hardware) disables all hardware
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timeouts and data should be reported as soon as possible.
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If the exact value cannot be set, then the next possible value
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.I greater
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than the given value should be set.
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.TP
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.BR LIRC_SET_REC_TIMEOUT_REPORTS " (\fIint\fP)"
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Enables
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.RI ( val
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is 1) or disables
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.RI (val
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is 0) timeout packages in
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.BR LIRC_MODE_MODE2 .
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By default, timeout reports should be turned off.
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.TP
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.BR LIRC_SET_REC_CARRIER " (\fIint\fP)"
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Set the receive carrier frequency (Hz).
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.TP
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After opening device, the first use of
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.BR LIRC_SET_REC_CARRIER_RANGE " (\fIint\fP)"
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sets the lower bound of the carrier range, second time the upper
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bound (Hz).
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.TP
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.BR LIRC_SET_MEASURE_CARRIER " (\fIint\fP)"
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Enables
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.RI ( val
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is 1) or disables
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.RI (val
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is 0) the measure mode
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If enabled, from the next key press on, the driver will send
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.BR LIRC_MODE2_FREQUENCY
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packets. By default this should be turned off.
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.TP
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.BR LIRC_GET_REC_RESOLUTION " (\fIvoid\fP)"
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Returns the driver resolution (microseconds).
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.TP
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.BR LIRC_GET_MIN_FILTER_PULSE " (\fIvoid\fP)", " " \
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LIRC_GET_MAX_FILTER_PULSE " (\fIvoid\fP)"
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Some devices are able to filter out spikes in the incoming signal
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using given filter rules.
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These ioctls return the hardware capabilities that describe the bounds
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of the possible filters.
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Filter settings depend on the IR protocols that are expected.
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lircd derives the settings from all protocols definitions found in its
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.BR lircd.conf (5)
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config file.
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.TP
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.BR LIRC_GET_MIN_FILTER_SPACE " (\fIvoid\fP)", " " \
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LIRC_GET_MAX_FILTER_SPACE " (\fIvoid\fP)"
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See
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.BR LIRC_GET_MIN_FILTER_PULSE .
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.TP
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.BR LIRC_SET_REC_FILTER " (\fIint\fP)"
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Pulses/spaces shorter than this (microseconds) are filtered out by
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hardware.
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.TP
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.BR LIRC_SET_REC_FILTER_PULSE " (\fIint\fP)", " " \
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LIRC_SET_REC_FILTER_SPACE " (\fIint\fP)"
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Pulses/spaces shorter than this (microseconds) are filtered out by
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hardware.
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If filters cannot be set independently for pulse/space, the
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corresponding ioctls must return an error and
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.BR LIRC_SET_REC_FILTER
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should be used instead.
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.TP
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.BR LIRC_SET_TRANSMITTER_MASK
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Enables the given set of transmitters.
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.RI val
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contains a bitmask where each enabled transmitter is a 1.
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The first transmitter is encoded by the least significant bit, etc.
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When an invalid bit mask is given, for example a bit is set even
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though the device does not have so many transmitters, returns the
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number of available transmitters and does nothing otherwise.
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.TP
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.BR LIRC_SET_WIDEBAND_RECEIVER " (\fIint\fP)"
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Some devices are equipped with a special wide band receiver which are
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intended to be used to learn the output of an existing remote.
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This ioctl can be used to enable
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.RI ( val
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equals 1) or disable
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.RI ( val
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equals 0) this functionality.
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This might be useful for devices that otherwise have narrow band
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receivers that prevent them to be used with certain remotes.
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Wide band receivers may also be more precise.
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On the other hand its disadvantage usually is reduced range of
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reception.
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.IP
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Note: wide band receiver may be implicitly enabled if you enable
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carrier reports.
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In that case it will be disabled as soon as you disable carrier reports.
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Trying to disable a wide band receiver while carrier reports are active
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will do nothing.
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.TP
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.BR LIRC_SETUP_START " (\fIvoid\fP)", " "LIRC_SETUP_END " (\fIvoid\fP)"
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Setting of several driver parameters can be optimized by encapsulating
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the actual ioctl calls with
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.BR LIRC_SETUP_START/LIRC_SETUP_END .
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When a driver receives a
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.BR LIRC_SETUP_START
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ioctl it can choose to not commit further setting changes to the
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hardware until a
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.BR LIRC_SETUP_END
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is received.
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But this is open to the driver implementation and every driver
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must also handle parameter changes which are not encapsulated by
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.BR LIRC_SETUP_START
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and
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.BR LIRC_SETUP_END .
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Drivers can also choose to ignore these ioctls.
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.TP
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.BR LIRC_NOTIFY_DECODE " (\fIvoid\fP)"
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This ioctl is called by
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.BR lircd(8)
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whenever a successful decoding of an incoming IR signal is possible.
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This can be used by supporting hardware to give visual user
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feedback, for example by flashing an LED.
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.SH FEATURES
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.P
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The features returned by
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.BR LIRC_GET_FEATURES
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is a bitmask combining the following bits:
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.TP 8
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.BR LIRC_CAN_REC_RAW
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The driver is capable of receiving using
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.BR LIRC_MODE_RAW .
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.TP 8
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.BR LIRC_CAN_REC_PULSE
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The driver is capable of receiving using
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.BR LIRC_MODE_PULSE .
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.TP 8
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.BR LIRC_CAN_REC_MODE2
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The driver is capable of receiving using
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.BR LIRC_MODE_MODE2 .
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.TP 8
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.BR LIRC_CAN_REC_LIRCCODE
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The driver is capable of receiving using
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.BR LIRC_MODE_LIRCCODE .
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.TP 8
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.BR LIRC_CAN_SET_SEND_CARRIER
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Driver supports changing the modulation frequency using
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.BR LIRC_SET_SEND_CARRIER .
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.TP 8
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.BR LIRC_CAN_SET_SEND_DUTY_CYCLE
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Driver supports changing the duty cycle using
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.BR LIRC_SET_SEND_DUTY_CYCLE .
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.TP 8
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.BR LIRC_CAN_SET_TRANSMITTER_MASK
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Driver supports changing the active transmitter(s) using
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.BR LIRC_SET_TRANSMITTER_MASK .
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.TP 8
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.BR LIRC_CAN_SET_REC_CARRIER
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Driver supports setting the receive carrier frequency using
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.BR LIRC_SET_REC_CARRIER .
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.TP 8
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.BR LIRC_CAN_SET_REC_DUTY_CYCLE_RANGE
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Driver supports
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.BR LIRC_SET_REC_DUTY_CYCLE_RANGE .
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.TP 8
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.BR LIRC_CAN_SET_REC_CARRIER_RANGE
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Driver supports
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.BR LIRC_SET_REC_CARRIER_RANGE .
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.TP 8
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.BR LIRC_CAN_GET_REC_RESOLUTION
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Driver supports
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.BR LIRC_GET_REC_RESOLUTION .
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.TP 8
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.BR LIRC_CAN_SET_REC_TIMEOUT
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Driver supports
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.BR LIRC_SET_REC_TIMEOUT .
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.TP 8
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.BR LIRC_CAN_SET_REC_FILTER
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Driver supports
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.BR LIRC_SET_REC_FILTER .
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.TP 8
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.BR LIRC_CAN_MEASURE_CARRIER
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Driver supports measuring of the modulation frequency using
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.BR LIRC_MEASURE_CARRIER .
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.TP 8
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.BR LIRC_CAN_USE_WIDEBAND_RECEIVER
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Driver supports learning mode using
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.BR LIRC_SET_WIDEBAND_RECEIVER .
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.TP 8
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.BR LIRC_CAN_NOTIFY_DECODE
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Driver supports
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.BR LIRC_NOTIFY_DECODE .
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.TP 8
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.BR LIRC_CAN_SEND_RAW
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Driver supports sending using
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.BR LIRC_SEND_RAW .
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.TP 8
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.BR LIRC_CAN_SEND_PULSE
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Driver supports sending using
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.BR LIRC_MODE_PULSE .
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.TP 8
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.BR LIRC_CAN_SEND_MODE2
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Driver supports sending using
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.BR LIRC_SEND_MODE2 .
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.TP 8
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.BR LIRC_CAN_SEND_LIRCCODE
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Driver supports sending.
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.BR LIRC_SEND_LIRCCODE
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(this is uncommon, since
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.BR LIRCCODE
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drivers reflect hardware like TV-cards which usually does not support
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sending.)
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.SH BUGS
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.P
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Using these devices requires the kernel source header file lirc.h.
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This file not being public is a bug, see
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https://bugzilla.kernel.org/show_bug.cgi?id=3D75751.
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For the time being the file is bundled in the lirc package,
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see http://www.lirc.org.
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.SH SEE ALSO
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.P
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https://www.kernel.org/doc/htmldocs/media_api/lirc_dev.html
|
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