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diff --git a/man4/lirc.4 b/man4/lirc.4 new file mode 100644 index 0000000..dcaae9b --- /dev/null +++ b/man4/lirc.4 @@ -0,0 +1,422 @@ +.\" Copyright (c) 2015-2016, Alec Leamas +.\" Copyright (c) 2018, Sean Young <sean@mess.org> +.\" +.\" SPDX-License-Identifier: GPL-2.0-or-later +.TH lirc 4 2023-05-03 "Linux man-pages 6.05.01" +.SH NAME +lirc \- lirc devices +.SH DESCRIPTION +The +.I /dev/lirc* +character devices provide a low-level +bidirectional interface to infra-red (IR) remotes. +Most of these devices can receive, and some can send. +When receiving or sending data, the driver works in two different modes +depending on the underlying hardware. +.PP +Some hardware (typically TV-cards) decodes the IR signal internally +and provides decoded button presses as scancode values. +Drivers for this kind of hardware work in +.B LIRC_MODE_SCANCODE +mode. +Such hardware usually does not support sending IR signals. +Furthermore, such hardware can only decode a limited set of IR protocols, +usually only the protocol of the specific remote which is +bundled with, for example, a TV-card. +.PP +Other hardware provides a stream of pulse/space durations. +Such drivers work in +.B LIRC_MODE_MODE2 +mode. +Such hardware can be used with (almost) any kind of remote. +This type of hardware can also be used in +.B LIRC_MODE_SCANCODE +mode, in which case the kernel IR decoders will decode the IR. +These decoders can be written in extended BPF (see +.BR bpf (2)) +and attached to the +.B lirc +device. +Sometimes, this kind of hardware also supports +sending IR data. +.PP +The \fBLIRC_GET_FEATURES\fR ioctl (see below) allows probing for whether +receiving and sending is supported, and in which modes, amongst other +features. +.\" +.SS Reading input with the LIRC_MODE_MODE2 mode +In the \fBLIRC_MODE_MODE2 mode\fR, the data returned by +.BR read (2) +provides 32-bit values representing a space or a pulse duration. +The time of the duration (microseconds) is encoded in the lower 24 bits. +Pulse (also known as flash) +indicates a duration of infrared light being detected, +and space (also known as gap) indicates a duration with no infrared. +If the duration of space exceeds the inactivity timeout, +a special timeout package is delivered, +which marks the end of a message. +The upper 8 bits indicate the type of package: +.TP 4 +.B LIRC_MODE2_SPACE +Value reflects a space duration (microseconds). +.TP 4 +.B LIRC_MODE2_PULSE +Value reflects a pulse duration (microseconds). +.TP 4 +.B LIRC_MODE2_FREQUENCY +Value reflects a frequency (Hz); see the +.B LIRC_SET_MEASURE_CARRIER_MODE +ioctl. +.TP 4 +.B LIRC_MODE2_TIMEOUT +Value reflects a space duration (microseconds). +The package reflects a timeout; see the +.B LIRC_SET_REC_TIMEOUT_REPORTS +ioctl. +.\" +.TP 4 +.B LIRC_MODE2_OVERFLOW +The IR receiver encountered an overflow, +and as a result data is missing +(since Linux 5.18). +.SS Reading input with the LIRC_MODE_SCANCODE mode +In the \fBLIRC_MODE_SCANCODE\fR +mode, the data returned by +.BR read (2) +reflects decoded button presses, in the struct \fIlirc_scancode\fR. +The scancode is stored in the \fIscancode\fR field, and the IR protocol +is stored in \fIrc_proto\fR. +This field has one the values of the \fIenum rc_proto\fR. +.\" +.SS Writing output with the LIRC_MODE_PULSE mode +The data written to the character device using +.BR write (2) +is a pulse/space sequence of integer values. +Pulses and spaces are only marked implicitly by their position. +The data must start and end with a pulse, thus it must always include +an odd number of samples. +The +.BR write (2) +function blocks until the data has been transmitted by the +hardware. +If more data is provided than the hardware can send, the +.BR write (2) +call fails with the error +.BR EINVAL . +.SS Writing output with the LIRC_MODE_SCANCODE mode +The data written to the character devices must be a single struct +\fIlirc_scancode\fR. +The \fIscancode\fR and \fIrc_proto\fR fields must +filled in, all other fields must be 0. +The kernel IR encoders will +convert the scancode to pulses and spaces. +The protocol or scancode is invalid, or the +.B lirc +device cannot transmit. +.SH IOCTL COMMANDS +.nf +#include <linux/lirc.h> /* But see BUGS */ +\& +int ioctl(int fd, int cmd, int *val); +.fi +.PP +The following +.BR ioctl (2) +operations are provided by the +.B lirc +character device to probe or change specific +.B lirc +hardware settings. +.SS Always Supported Commands +\fI/dev/lirc*\fR devices always support the following commands: +.TP 4 +.BR LIRC_GET_FEATURES " (\fIvoid\fP)" +Returns a bit mask of combined features bits; see FEATURES. +.PP +If a device returns an error code for +.BR LIRC_GET_FEATURES , +it is safe to assume it is not a +.B lirc +device. +.\" +.SS Optional Commands +Some +.B lirc +devices support the commands listed below. +Unless otherwise stated, these fail with the error \fBENOTTY\fR if the +operation isn't supported, or with the error \fBEINVAL\fR if the operation +failed, or invalid arguments were provided. +If a driver does not announce support of certain features, invoking +the corresponding ioctls will fail with the error +.BR ENOTTY . +.TP +.BR LIRC_GET_REC_MODE " (\fIvoid\fP)" +If the +.B lirc +device has no receiver, this operation fails with the error +.BR ENOTTY . +Otherwise, it returns the receive mode, which will be one of: +.RS +.TP +.B LIRC_MODE_MODE2 +The driver returns a sequence of pulse/space durations. +.TP +.B LIRC_MODE_SCANCODE +The driver returns struct +.I lirc_scancode +values, each of which represents +a decoded button press. +.RE +.TP +.BR LIRC_SET_REC_MODE " (\fIint\fP)" +Set the receive mode. +.I val +is either +.B LIRC_MODE_SCANCODE +or +.BR LIRC_MODE_MODE2 . +If the +.B lirc +device has no receiver, this operation fails with the error +.B ENOTTY. +.TP +.BR LIRC_GET_SEND_MODE " (\fIvoid\fP)" +Return the send mode. +.B LIRC_MODE_PULSE +or +.B LIRC_MODE_SCANCODE +is supported. +If the +.B lirc +device cannot send, this operation fails with the error +.B ENOTTY. +.TP +.BR LIRC_SET_SEND_MODE " (\fIint\fP)" +Set the send mode. +.I val +is either +.B LIRC_MODE_SCANCODE +or +.BR LIRC_MODE_PULSE . +If the +.B lirc +device cannot send, this operation fails with the error +.BR ENOTTY . +.TP +.BR LIRC_SET_SEND_CARRIER " (\fIint\fP)" +Set the modulation frequency. +The argument is the frequency (Hz). +.TP +.BR LIRC_SET_SEND_DUTY_CYCLE " (\fIint\fP)" +Set the carrier duty cycle. +.I val +is a number in the range [0,100] which +describes the pulse width as a percentage of the total cycle. +Currently, no special meaning is defined for 0 or 100, but the values +are reserved for future use. +.TP +.BR LIRC_GET_MIN_TIMEOUT " (\fIvoid\fP)", " "\ +LIRC_GET_MAX_TIMEOUT " (\fIvoid\fP)" +Some devices have internal timers that can be used to detect when +there has been no IR activity for a long time. +This can help +.BR lircd (8) +in detecting that an IR signal is finished and can speed up the +decoding process. +These operations +return integer values with the minimum/maximum timeout that can be +set (microseconds). +Some devices have a fixed timeout. +For such drivers, +.B LIRC_GET_MIN_TIMEOUT +and +.B LIRC_GET_MAX_TIMEOUT +will fail with the error +.BR ENOTTY . +.TP +.BR LIRC_SET_REC_TIMEOUT " (\fIint\fP)" +Set the integer value for IR inactivity timeout (microseconds). +To be accepted, the value must be within the limits defined by +.B LIRC_GET_MIN_TIMEOUT +and +.BR LIRC_GET_MAX_TIMEOUT . +A value of 0 (if supported by the hardware) disables all hardware +timeouts and data should be reported as soon as possible. +If the exact value cannot be set, then the next possible value +.I greater +than the given value should be set. +.TP +.BR LIRC_GET_REC_TIMEOUT " (\fIvoid\fP)" +Return the current inactivity timeout (microseconds). +Available since Linux 4.18. +.TP +.BR LIRC_SET_REC_TIMEOUT_REPORTS " (\fIint\fP)" +Enable +.RI ( val +is 1) or disable +.RI ( val +is 0) timeout packages in +.BR LIRC_MODE_MODE2 . +The behavior of this operation has varied across kernel versions: +.RS +.IP \[bu] 3 +Since Linux 5.17: +timeout packages are always enabled and this ioctl is a no-op. +.IP \[bu] +Since Linux 4.16: +timeout packages are enabled by default. +Each time the +.B lirc +device is opened, the +.B LIRC_SET_REC_TIMEOUT +operation can be used to disable (and, if desired, to later re-enable) +the timeout on the file descriptor. +.IP \[bu] +In Linux 4.15 and earlier: +timeout packages are disabled by default, and enabling them (via +.BR LIRC_SET_REC_TIMEOUT ) +on any file descriptor associated with the +.B lirc +device has the effect of enabling timeouts for all file descriptors +referring to that device (until timeouts are disabled again). +.RE +.TP +.BR LIRC_SET_REC_CARRIER " (\fIint\fP)" +Set the upper bound of the receive carrier frequency (Hz). +See +.BR LIRC_SET_REC_CARRIER_RANGE . +.TP +.BR LIRC_SET_REC_CARRIER_RANGE " (\fIint\fP)" +Sets the lower bound of the receive carrier frequency (Hz). +For this to take affect, first set the lower bound using the +.B LIRC_SET_REC_CARRIER_RANGE +ioctl, and then the upper bound using the +.B LIRC_SET_REC_CARRIER +ioctl. +.TP +.BR LIRC_SET_MEASURE_CARRIER_MODE " (\fIint\fP)" +Enable +.RI ( val +is 1) or disable +.RI ( val +is 0) the measure mode. +If enabled, from the next key press on, the driver will send +.B LIRC_MODE2_FREQUENCY +packets. +By default, this should be turned off. +.TP +.BR LIRC_GET_REC_RESOLUTION " (\fIvoid\fP)" +Return the driver resolution (microseconds). +.TP +.BR LIRC_SET_TRANSMITTER_MASK " (\fIint\fP)" +Enable the set of transmitters specified in +.IR val , +which contains a bit mask where each enabled transmitter is a 1. +The first transmitter is encoded by the least significant bit, and so on. +When an invalid bit mask is given, for example a bit is set even +though the device does not have so many transmitters, +this operation returns the +number of available transmitters and does nothing otherwise. +.TP +.BR LIRC_SET_WIDEBAND_RECEIVER " (\fIint\fP)" +Some devices are equipped with a special wide band receiver which is +intended to be used to learn the output of an existing remote. +This ioctl can be used to enable +.RI ( val +equals 1) or disable +.RI ( val +equals 0) this functionality. +This might be useful for devices that otherwise have narrow band +receivers that prevent them to be used with certain remotes. +Wide band receivers may also be more precise. +On the other hand, their disadvantage usually is reduced range of +reception. +.IP +Note: wide band receiver may be implicitly enabled if you enable +carrier reports. +In that case, it will be disabled as soon as you disable carrier reports. +Trying to disable a wide band receiver while carrier reports are active +will do nothing. +.\" +.SH FEATURES +the +.B LIRC_GET_FEATURES +ioctl returns a bit mask describing features of the driver. +The following bits may be returned in the mask: +.TP +.B LIRC_CAN_REC_MODE2 +The driver is capable of receiving using +.BR LIRC_MODE_MODE2 . +.TP +.B LIRC_CAN_REC_SCANCODE +The driver is capable of receiving using +.BR LIRC_MODE_SCANCODE . +.TP +.B LIRC_CAN_SET_SEND_CARRIER +The driver supports changing the modulation frequency using +.BR LIRC_SET_SEND_CARRIER . +.TP +.B LIRC_CAN_SET_SEND_DUTY_CYCLE +The driver supports changing the duty cycle using +.BR LIRC_SET_SEND_DUTY_CYCLE . +.TP +.B LIRC_CAN_SET_TRANSMITTER_MASK +The driver supports changing the active transmitter(s) using +.BR LIRC_SET_TRANSMITTER_MASK . +.TP +.B LIRC_CAN_SET_REC_CARRIER +The driver supports setting the receive carrier frequency using +.BR LIRC_SET_REC_CARRIER . +Any +.B lirc +device since the drivers were merged in Linux 2.6.36 +must have +.B LIRC_CAN_SET_REC_CARRIER_RANGE +set if +.B LIRC_CAN_SET_REC_CARRIER +feature is set. +.TP +.B LIRC_CAN_SET_REC_CARRIER_RANGE +The driver supports +.BR LIRC_SET_REC_CARRIER_RANGE . +The lower bound of the carrier must first be set using the +.B LIRC_SET_REC_CARRIER_RANGE +ioctl, before using the +.B LIRC_SET_REC_CARRIER +ioctl to set the upper bound. +.TP +.B LIRC_CAN_GET_REC_RESOLUTION +The driver supports +.BR LIRC_GET_REC_RESOLUTION . +.TP +.B LIRC_CAN_SET_REC_TIMEOUT +The driver supports +.BR LIRC_SET_REC_TIMEOUT . +.TP +.B LIRC_CAN_MEASURE_CARRIER +The driver supports measuring of the modulation frequency using +.BR LIRC_SET_MEASURE_CARRIER_MODE . +.TP +.B LIRC_CAN_USE_WIDEBAND_RECEIVER +The driver supports learning mode using +.BR LIRC_SET_WIDEBAND_RECEIVER . +.TP +.B LIRC_CAN_SEND_PULSE +The driver supports sending using +.B LIRC_MODE_PULSE +or +.B LIRC_MODE_SCANCODE +.\" +.SH BUGS +Using these devices requires the kernel source header file +.IR lirc.h . +This file is not available before Linux 4.6. +Users of older kernels could use the file bundled in +.UR http://www.lirc.org +.UE . +.\" +.SH SEE ALSO +\fBir\-ctl\fP(1), \fBlircd\fP(8),\ \fBbpf\fP(2) +.PP +.UR https://www.kernel.org/\:doc/\:html/\:latest/\:userspace\-api/\:media/\:rc/\:lirc\-dev.html +.UE |