lirc

In the LIRC_MODE_MODE2 mode, the data returned by 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. The upper 8 bits indicate the type of package:

LIRC_MODE2_SPACE

Value reflects a space duration (microseconds).

LIRC_MODE2_PULSE

Value reflects a pulse duration (microseconds).

LIRC_MODE2_FREQUENCY

Value reflects a frequency (Hz); see the LIRC_SET_MEASURE_CARRIER_MODE ioctl.

LIRC_MODE2_TIMEOUT

Value reflects a space duration (microseconds). The package reflects a timeout; see the LIRC_SET_REC_TIMEOUT_REPORTS ioctl.

In the LIRC_MODE_SCANCODE mode, the data returned by read(2) reflects decoded button presses, in the struct lirc_scancode. The scancode is stored in the scancode field, and the IR protocol is stored in rc_proto. This field has one the values of the enum rc_proto.

The data written to the character device using 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 write(2) function blocks until the data has been transmitted by the hardware. If more data is provided than the hardware can send, the write(2) call fails with the error EINVAL.

The data written to the character devices must be a single struct lirc_scancode. The scancode and rc_proto 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 lirc device cannot transmit.

/dev/lirc* devices always support the following commands:

LIRC_GET_FEATURES (void)

Returns a bit mask of combined features bits; see Features.

If a device returns an error code for LIRC_GET_FEATURES, it is safe to assume it is not a lirc device.

Some lirc devices support the commands listed below. Unless otherwise stated, these fail with the error ENOTTY if the operation isn't supported, or with the error EINVAL 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 ENOTTY.

LIRC_GET_REC_MODE (void)

If the lirc device has no receiver, this operation fails with the error ENOTTY. Otherwise, it returns the receive mode, which will be one of:

LIRC_MODE_MODE2

The driver returns a sequence of pulse/space durations.

LIRC_MODE_SCANCODE

The driver returns struct lirc_scancode values, each of which represents a decoded button press.

LIRC_SET_REC_MODE (int)

Set the receive mode. val is either LIRC_MODE_SCANCODE or LIRC_MODE_MODE2. If the lirc device has no receiver, this operation fails with the error ENOTTY.

LIRC_GET_SEND_MODE (void)

Return the send mode. LIRC_MODE_PULSE or LIRC_MODE_SCANCODE is supported. If the lirc device cannot send, this operation fails with the error ENOTTY.

LIRC_SET_SEND_MODE (int)

Set the send mode. val is either LIRC_MODE_SCANCODE or LIRC_MODE_PULSE. If the lirc device cannot send, this operation fails with the error ENOTTY.

LIRC_SET_SEND_CARRIER (int)

Set the modulation frequency. The argument is the frequency (Hz).

LIRC_SET_SEND_DUTY_CYCLE (int)

Set the carrier duty cycle. 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.

LIRC_GET_MIN_TIMEOUT (void), LIRC_GET_MAX_TIMEOUT (void)

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 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, LIRC_GET_MIN_TIMEOUT and LIRC_GET_MAX_TIMEOUT will fail with the error ENOTTY.

LIRC_SET_REC_TIMEOUT (int)

Set the integer value for IR inactivity timeout (microseconds). To be accepted, the value must be within the limits defined by LIRC_GET_MIN_TIMEOUT and 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 greater than the given value should be set.

LIRC_GET_REC_TIMEOUT (void)

Return the current inactivity timeout (microseconds). Available since Linux 4.18.

LIRC_SET_REC_TIMEOUT_REPORTS (int)

Enable (val is 1) or disable (val is 0) timeout packages in LIRC_MODE_MODE2. The behavior of this operation has varied across kernel versions:

• Since Linux 4.16: each time the lirc device is opened, timeout reports are by default enabled for the resulting file descriptor. The LIRC_SET_REC_TIMEOUT operation can be used to disable (and, if desired, to later re-enable) the timeout on the file descriptor.
• In Linux 4.15 and earlier: timeout reports are disabled by default, and enabling them (via LIRC_SET_REC_TIMEOUT) on any file descriptor associated with the lirc device has the effect of enabling timeouts for all file descriptors referring to that device (until timeouts are disabled again).

LIRC_SET_REC_CARRIER (int)

Set the upper bound of the receive carrier frequency (Hz). See LIRC_SET_REC_CARRIER_RANGE.

LIRC_SET_REC_CARRIER_RANGE (int)

Sets the lower bound of the receive carrier frequency (Hz). For this to take affect, first set the lower bound using the LIRC_SET_REC_CARRIER_RANGE ioctl, and then the upper bound using the LIRC_SET_REC_CARRIER ioctl.

LIRC_SET_MEASURE_CARRIER_MODE (int)

Enable (val is 1) or disable (val is 0) the measure mode. If enabled, from the next key press on, the driver will send LIRC_MODE2_FREQUENCY packets. By default, this should be turned off.

LIRC_GET_REC_RESOLUTION (void)

Return the driver resolution (microseconds).

LIRC_SET_TRANSMITTER_MASK (int)

Enable the set of transmitters specified in 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.

LIRC_SET_WIDEBAND_RECEIVER (int)

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 (val equals 1) or disable (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.

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.