{ "content": [ { "type": "text", "text": "# lirc(4) (man)\n\n**Summary:** lirc - lirc devices\n\n## See Also\n\n- ir-ctl(1)\n- lircd(8)\n- bpf(2)\n\n## Section Outline\n\n- **NAME** (2 lines)\n- **DESCRIPTION** (55 lines)\n- **IOCTL COMMANDS** (11 lines) — 2 subsections\n - Always Supported Commands (8 lines)\n - Optional Commands (104 lines)\n- **FEATURES** (45 lines)\n- **BUGS** (4 lines)\n- **SEE ALSO** (4 lines)\n- **COLOPHON** (7 lines)\n\n## Full Content\n\n### NAME\n\nlirc - lirc devices\n\n### DESCRIPTION\n\nThe /dev/lirc* character devices provide a low-level bidirectional interface to infra-red\n(IR) remotes. Most of these devices can receive, and some can send. When receiving or send‐\ning data, the driver works in two different modes depending on the underlying hardware.\n\nSome hardware (typically TV-cards) decodes the IR signal internally and provides decoded but‐\nton presses as scancode values. Drivers for this kind of hardware work in LIRCMODESCANCODE\nmode. Such hardware usually does not support sending IR signals. Furthermore, such hardware\ncan only decode a limited set of IR protocols, usually only the protocol of the specific re‐\nmote which is bundled with, for example, a TV-card.\n\nOther hardware provides a stream of pulse/space durations. Such drivers work in\nLIRCMODEMODE2 mode. Sometimes, this kind of hardware also supports sending IR data. Such\nhardware can be used with (almost) any kind of remote. This type of hardware can also be\nused in LIRCMODESCANCODE mode, in which case the kernel IR decoders will decode the IR.\nThese decoders can be written in extended BPF (see bpf(2)) and attached to the lirc device.\n\nThe LIRCGETFEATURES ioctl (see below) allows probing for whether receiving and sending is\nsupported, and in which modes, amongst other features.\n\nReading input with the LIRCMODEMODE2 mode\nIn the LIRCMODEMODE2 mode, the data returned by read(2) provides 32-bit values representing\na space or a pulse duration. The time of the duration (microseconds) is encoded in the lower\n24 bits. The upper 8 bits indicate the type of package:\n\nLIRCMODE2SPACE\nValue reflects a space duration (microseconds).\n\nLIRCMODE2PULSE\nValue reflects a pulse duration (microseconds).\n\nLIRCMODE2FREQUENCY\nValue reflects a frequency (Hz); see the LIRCSETMEASURECARRIERMODE ioctl.\n\nLIRCMODE2TIMEOUT\nValue reflects a space duration (microseconds). The package reflects a timeout; see the\nLIRCSETRECTIMEOUTREPORTS ioctl.\n\nReading input with the LIRCMODESCANCODE mode\nIn the LIRCMODESCANCODE mode, the data returned by read(2) reflects decoded button presses,\nin the struct lircscancode. The scancode is stored in the scancode field, and the IR proto‐\ncol is stored in rcproto. This field has one the values of the enum rcproto.\n\nWriting output with the LIRCMODEPULSE mode\nThe data written to the character device using write(2) is a pulse/space sequence of integer\nvalues. Pulses and spaces are only marked implicitly by their position. The data must start\nand end with a pulse, thus it must always include an odd number of samples. The write(2)\nfunction blocks until the data has been transmitted by the hardware. If more data is pro‐\nvided than the hardware can send, the write(2) call fails with the error EINVAL.\n\nWriting output with the LIRCMODESCANCODE mode\nThe data written to the character devices must be a single struct lircscancode. The scan‐\ncode and rcproto fields must filled in, all other fields must be 0. The kernel IR encoders\nwill convert the scancode to pulses and spaces. The protocol or scancode is invalid, or the\nlirc device cannot transmit.\n\n### IOCTL COMMANDS\n\nThe LIRC device's ioctl definition is bound by the ioctl function definition of struct\nfileoperations, leaving us with an unsigned int for the ioctl command and an unsigned long\nfor the argument. For the purposes of ioctl portability across 32-bit and 64-bit architec‐\ntures, these values are capped to their 32-bit sizes.\n\n#include /* But see BUGS */\nint ioctl(int fd, int cmd, ...);\n\nThe following ioctls can be used to probe or change specific lirc hardware settings. Many\nrequire a third argument, usually an int. referred to below as val.\n\n#### Always Supported Commands\n\n/dev/lirc* devices always support the following commands:\n\nLIRCGETFEATURES (void)\nReturns a bit mask of combined features bits; see FEATURES.\n\nIf a device returns an error code for LIRCGETFEATURES, it is safe to assume it is not a\nlirc device.\n\n#### Optional Commands\n\nSome lirc devices support the commands listed below. Unless otherwise stated, these fail\nwith the error ENOTTY if the operation isn't supported, or with the error EINVAL if the oper‐\nation failed, or invalid arguments were provided. If a driver does not announce support of\ncertain features, invoking the corresponding ioctls will fail with the error ENOTTY.\n\nLIRCGETRECMODE (void)\nIf the lirc device has no receiver, this operation fails with the error ENOTTY. Oth‐\nerwise, it returns the receive mode, which will be one of:\n\nLIRCMODEMODE2\nThe driver returns a sequence of pulse/space durations.\n\nLIRCMODESCANCODE\nThe driver returns struct lircscancode values, each of which represents a de‐\ncoded button press.\n\nLIRCSETRECMODE (int)\nSet the receive mode. val is either LIRCMODESCANCODE or LIRCMODEMODE2. If the\nlirc device has no receiver, this operation fails with the error ENOTTY.\n\nLIRCGETSENDMODE (void)\nReturn the send mode. LIRCMODEPULSE or LIRCMODESCANCODE is supported. If the\nlirc device cannot send, this operation fails with the error ENOTTY.\n\nLIRCSETSENDMODE (int)\nSet the send mode. val is either LIRCMODESCANCODE or LIRCMODEPULSE. If the lirc\ndevice cannot send, this operation fails with the error ENOTTY.\n\nLIRCSETSENDCARRIER (int)\nSet the modulation frequency. The argument is the frequency (Hz).\n\nLIRCSETSENDDUTYCYCLE (int)\nSet the carrier duty cycle. val is a number in the range [0,100] which describes the\npulse width as a percentage of the total cycle. Currently, no special meaning is de‐\nfined for 0 or 100, but the values are reserved for future use.\n\nLIRCGETMINTIMEOUT (void), LIRCGETMAXTIMEOUT (void)\nSome devices have internal timers that can be used to detect when there has been no IR\nactivity for a long time. This can help lircd(8) in detecting that an IR signal is\nfinished and can speed up the decoding process. These operations return integer val‐\nues with the minimum/maximum timeout that can be set (microseconds). Some devices\nhave a fixed timeout. For such drivers, LIRCGETMINTIMEOUT and LIRCGETMAXTIMEOUT\nwill fail with the error ENOTTY.\n\nLIRCSETRECTIMEOUT (int)\nSet the integer value for IR inactivity timeout (microseconds). To be accepted, the\nvalue must be within the limits defined by LIRCGETMINTIMEOUT and LIRCGETMAXTIME‐‐\nOUT. A value of 0 (if supported by the hardware) disables all hardware timeouts and\ndata should be reported as soon as possible. If the exact value cannot be set, then\nthe next possible value greater than the given value should be set.\n\nLIRCGETRECTIMEOUT (void)\nReturn the current inactivity timeout (microseconds). Available since Linux 4.18.\n\nLIRCSETRECTIMEOUTREPORTS (int)\nEnable (val is 1) or disable (val is 0) timeout packages in LIRCMODEMODE2. The be‐\nhavior of this operation has varied across kernel versions:\n\n* Since Linux 4.16: each time the lirc device is opened, timeout reports are by de‐\nfault enabled for the resulting file descriptor. The LIRCSETRECTIMEOUT opera‐\ntion can be used to disable (and, if desired, to later re-enable) the timeout on\nthe file descriptor.\n\n* In Linux 4.15 and earlier: timeout reports are disabled by default, and enabling\nthem (via LIRCSETRECTIMEOUT) on any file descriptor associated with the lirc de‐\nvice has the effect of enabling timeouts for all file descriptors referring to that\ndevice (until timeouts are disabled again).\n\nLIRCSETRECCARRIER (int)\nSet the upper bound of the receive carrier frequency (Hz). See LIRCSETRECCAR‐‐\nRIERRANGE.\n\nLIRCSETRECCARRIERRANGE (int)\nSets the lower bound of the receive carrier frequency (Hz). For this to take affect,\nfirst set the lower bound using the LIRCSETRECCARRIERRANGE ioctl, and then the up‐\nper bound using the LIRCSETRECCARRIER ioctl.\n\nLIRCSETMEASURECARRIERMODE (int)\nEnable (val is 1) or disable (val is 0) the measure mode. If enabled, from the next\nkey press on, the driver will send LIRCMODE2FREQUENCY packets. By default, this\nshould be turned off.\n\nLIRCGETRECRESOLUTION (void)\nReturn the driver resolution (microseconds).\n\nLIRCSETTRANSMITTERMASK (int)\nEnable the set of transmitters specified in val, which contains a bit mask where each\nenabled transmitter is a 1. The first transmitter is encoded by the least significant\nbit, and so on. When an invalid bit mask is given, for example a bit is set even\nthough the device does not have so many transmitters, this operation returns the num‐\nber of available transmitters and does nothing otherwise.\n\nLIRCSETWIDEBANDRECEIVER (int)\nSome devices are equipped with a special wide band receiver which is intended to be\nused to learn the output of an existing remote. This ioctl can be used to enable (val\nequals 1) or disable (val equals 0) this functionality. This might be useful for de‐\nvices that otherwise have narrow band receivers that prevent them to be used with cer‐\ntain remotes. Wide band receivers may also be more precise. On the other hand, their\ndisadvantage usually is reduced range of reception.\n\nNote: wide band receiver may be implicitly enabled if you enable carrier reports. In\nthat case, it will be disabled as soon as you disable carrier reports. Trying to dis‐\nable a wide band receiver while carrier reports are active will do nothing.\n\n### FEATURES\n\nthe LIRCGETFEATURES ioctl returns a bit mask describing features of the driver. The fol‐\nlowing bits may be returned in the mask:\n\nLIRCCANRECMODE2\nThe driver is capable of receiving using LIRCMODEMODE2.\n\nLIRCCANRECSCANCODE\nThe driver is capable of receiving using LIRCMODESCANCODE.\n\nLIRCCANSETSENDCARRIER\nThe driver supports changing the modulation frequency using LIRCSETSENDCARRIER.\n\nLIRCCANSETSENDDUTYCYCLE\nThe driver supports changing the duty cycle using LIRCSETSENDDUTYCYCLE.\n\nLIRCCANSETTRANSMITTERMASK\nThe driver supports changing the active transmitter(s) using LIRCSETTRANSMIT‐‐\nTERMASK.\n\nLIRCCANSETRECCARRIER\nThe driver supports setting the receive carrier frequency using LIRCSETRECCARRIER.\nAny lirc device since the drivers were merged in kernel release 2.6.36 must have\nLIRCCANSETRECCARRIERRANGE set if LIRCCANSETRECCARRIER feature is set.\n\nLIRCCANSETRECCARRIERRANGE\nThe driver supports LIRCSETRECCARRIERRANGE. The lower bound of the carrier must\nfirst be set using the LIRCSETRECCARRIERRANGE ioctl, before using the\nLIRCSETRECCARRIER ioctl to set the upper bound.\n\nLIRCCANGETRECRESOLUTION\nThe driver supports LIRCGETRECRESOLUTION.\n\nLIRCCANSETRECTIMEOUT\nThe driver supports LIRCSETRECTIMEOUT.\n\nLIRCCANMEASURECARRIER\nThe driver supports measuring of the modulation frequency using LIRCSETMEASURECAR‐‐\nRIERMODE.\n\nLIRCCANUSEWIDEBANDRECEIVER\nThe driver supports learning mode using LIRCSETWIDEBANDRECEIVER.\n\nLIRCCANSENDPULSE\nThe driver supports sending using LIRCMODEPULSE or LIRCMODESCANCODE\n\n### BUGS\n\nUsing these devices requires the kernel source header file lirc.h. This file is not avail‐\nable before kernel release 4.6. Users of older kernels could use the file bundled in\n⟨http://www.lirc.org⟩.\n\n### SEE ALSO\n\nir-ctl(1), lircd(8), bpf(2)\n\nhttps://www.kernel.org/doc/html/latest/media/uapi/rc/lirc-dev.html\n\n### COLOPHON\n\nThis page is part of release 5.10 of the Linux man-pages project. A description of the\nproject, information about reporting bugs, and the latest version of this page, can be found\nat https://www.kernel.org/doc/man-pages/.\n\n\n\nLinux 2019-03-06 LIRC(4)\n\n" } ], "structuredContent": { "command": "lirc", "section": "4", "mode": "man", "summary": "lirc - lirc devices", "synopsis": null, "flags": [], "examples": [], "see_also": [ { "name": "ir-ctl", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/ir-ctl/1/json" }, { "name": "lircd", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/lircd/8/json" }, { "name": "bpf", "section": "2", "url": "https://www.chedong.com/phpMan.php/man/bpf/2/json" } ], "section_outline": [ { "name": "NAME", "lines": 2, "subsections": [] }, { "name": "DESCRIPTION", "lines": 55, "subsections": [] }, { "name": "IOCTL COMMANDS", "lines": 11, "subsections": [ { "name": "Always Supported Commands", "lines": 8 }, { "name": "Optional Commands", "lines": 104 } ] }, { "name": "FEATURES", "lines": 45, "subsections": [] }, { "name": "BUGS", "lines": 4, "subsections": [] }, { "name": "SEE ALSO", "lines": 4, "subsections": [] }, { "name": "COLOPHON", "lines": 7, "subsections": [] } ] } }