102 lines
2.9 KiB
ReStructuredText
102 lines
2.9 KiB
ReStructuredText
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.. -*- coding: utf-8; mode: rst -*-
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.. _lirc_dev_intro:
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************
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Introduction
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************
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The LIRC device interface is a bi-directional interface for transporting
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raw IR data between userspace and kernelspace. Fundamentally, it is just
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a chardev (/dev/lircX, for X = 0, 1, 2, ...), with a number of standard
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struct file_operations defined on it. With respect to transporting raw
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IR data to and fro, the essential fops are read, write and ioctl.
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Example dmesg output upon a driver registering w/LIRC:
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.. code-block:: none
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$ dmesg |grep lirc_dev
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lirc_dev: IR Remote Control driver registered, major 248
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rc rc0: lirc_dev: driver ir-lirc-codec (mceusb) registered at minor = 0
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What you should see for a chardev:
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.. code-block:: none
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$ ls -l /dev/lirc*
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crw-rw---- 1 root root 248, 0 Jul 2 22:20 /dev/lirc0
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.. _lirc_modes:
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**********
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LIRC modes
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**********
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LIRC supports some modes of receiving and sending IR codes, as shown
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on the following table.
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.. _lirc-mode-mode2:
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``LIRC_MODE_MODE2``
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The driver returns a sequence of pulse and space codes to userspace,
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as a series of u32 values.
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This mode is used only for IR receive.
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The upper 8 bits determine the packet type, and the lower 24 bits
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the payload. Use ``LIRC_VALUE()`` macro to get the payload, and
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the macro ``LIRC_MODE2()`` will give you the type, which
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is one of:
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``LIRC_MODE2_PULSE``
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Signifies the presence of IR in microseconds.
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``LIRC_MODE2_SPACE``
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Signifies absence of IR in microseconds.
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``LIRC_MODE2_FREQUENCY``
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If measurement of the carrier frequency was enabled with
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:ref:`lirc_set_measure_carrier_mode` then this packet gives you
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the carrier frequency in Hertz.
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``LIRC_MODE2_TIMEOUT``
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If timeout reports are enabled with
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:ref:`lirc_set_rec_timeout_reports`, when the timeout set with
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:ref:`lirc_set_rec_timeout` expires due to no IR being detected,
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this packet will be sent, with the number of microseconds with
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no IR.
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.. _lirc-mode-lirccode:
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``LIRC_MODE_LIRCCODE``
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This mode can be used for IR receive and send.
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The IR signal is decoded internally by the receiver, or encoded by the
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transmitter. The LIRC interface represents the scancode as byte string,
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which might not be a u32, it can be any length. The value is entirely
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driver dependent. This mode is used by some older lirc drivers.
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The length of each code depends on the driver, which can be retrieved
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with :ref:`lirc_get_length`. This length is used both
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for transmitting and receiving IR.
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.. _lirc-mode-pulse:
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``LIRC_MODE_PULSE``
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In pulse mode, a sequence of pulse/space integer values are written to the
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lirc device using :ref:`lirc-write`.
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The values are alternating pulse and space lengths, in microseconds. The
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first and last entry must be a pulse, so there must be an odd number
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of entries.
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This mode is used only for IR send.
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