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media: lirc: document LIRC_MODE_SCANCODE

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Lirc supports a new mode which requires documentation.

Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
This commit is contained in:
Sean Young
2017-02-25 06:51:34 -05:00
committed by Mauro Carvalho Chehab
parent b66218fddf
commit 7d402db89b
7 changed files with 118 additions and 15 deletions
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51
Documentation/media/uapi/rc/lirc-dev-intro.rst
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@@ -6,11 +6,12 @@
Introduction
************
The LIRC device interface is a bi-directional interface for transporting
raw IR data between userspace and kernelspace. Fundamentally, it is just
a chardev (/dev/lircX, for X = 0, 1, 2, ...), with a number of standard
struct file_operations defined on it. With respect to transporting raw
IR data to and fro, the essential fops are read, write and ioctl.
LIRC stands for Linux Infrared Remote Control. The LIRC device interface is
a bi-directional interface for transporting raw IR and decoded scancodes
data between userspace and kernelspace. Fundamentally, it is just a chardev
(/dev/lircX, for X = 0, 1, 2, ...), with a number of standard struct
file_operations defined on it. With respect to transporting raw IR and
decoded scancodes to and fro, the essential fops are read, write and ioctl.
Example dmesg output upon a driver registering w/LIRC:
@@ -36,6 +37,46 @@ LIRC modes
LIRC supports some modes of receiving and sending IR codes, as shown
on the following table.
.. _lirc-mode-scancode:
.. _lirc-scancode-flag-toggle:
.. _lirc-scancode-flag-repeat:
``LIRC_MODE_SCANCODE``
This mode is for both sending and receiving IR.
For transmitting (aka sending), create a ``struct lirc_scancode`` with
the desired scancode set in the ``scancode`` member, ``rc_proto`` set
the IR protocol, and all other members set to 0. Write this struct to
the lirc device.
For receiving, you read ``struct lirc_scancode`` from the lirc device,
with ``scancode`` set to the received scancode and the IR protocol
``rc_proto``. If the scancode maps to a valid key code, this is set
in the ``keycode`` field, else it is set to ``KEY_RESERVED``.
The ``flags`` can have ``LIRC_SCANCODE_FLAG_TOGGLE`` set if the toggle
bit is set in protocols that support it (e.g. rc-5 and rc-6), or
``LIRC_SCANCODE_FLAG_REPEAT`` for when a repeat is received for protocols
that support it (e.g. nec).
In the Sanyo and NEC protocol, if you hold a button on remote, rather than
repeating the entire scancode, the remote sends a shorter message with
no scancode, which just means button is held, a "repeat". When this is
received, the ``LIRC_SCANCODE_FLAG_REPEAT`` is set and the scancode and
keycode is repeated.
With nec, there is no way to distinguish "button hold" from "repeatedly
pressing the same button". The rc-5 and rc-6 protocols have a toggle bit.
When a button is released and pressed again, the toggle bit is inverted.
If the toggle bit is set, the ``LIRC_SCANCODE_FLAG_TOGGLE`` is set.
The ``timestamp`` field is filled with the time nanoseconds
(in ``CLOCK_MONOTONIC``) when the scancode was decoded.
An ``enum rc_proto`` in the :ref:`lirc_header` lists all the supported
IR protocols.
.. _lirc-mode-mode2:
``LIRC_MODE_MODE2``