Multicolor LED Handling under Linux

Multicolor class와 색상 제어

Multicolor class는 여러 monochrome LED를 한 group으로 묶고 최종 조합 색상의 hue와 lightness를 제어합니다. Hue는 `multi_intensity` array file, lightness는 공통 `brightness` file이 담당합니다.

Multicolor file은 LED class framework가 만든 parent node 아래에 있고 color를 array index로 묶습니다. 각 color LED는 `multi_*` file의 같은 index에 대응하지만 순서는 임의이므로 `multi_index`를 읽어 color 이름과 index를 확인해야 합니다.

`multi_index`는 각 `multi_*` array에서 사용하는 color string 목록입니다. `multi_intensity`는 각 color intensity를 읽고 쓰는 array이며, color update를 적용하려면 모든 element를 순서대로 한 번에 써야 합니다.

.. SPDX-License-Identifier: GPL-2.0

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Multicolor LED handling under Linux
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Description
===========
The multicolor class groups monochrome LEDs and allows controlling two
aspects of the final combined color: hue and lightness. The former is
controlled via the multi_intensity array file and the latter is controlled
via brightness file.

Multicolor Class Control
========================
The multicolor class presents files that groups the colors as indexes in an
array.  These files are children under the LED parent node created by the
led_class framework.  The led_class framework is documented in led-class.rst
within this documentation directory.

Each colored LED will be indexed under the ``multi_*`` files. The order of the
colors will be arbitrary. The ``multi_index`` file can be read to determine the
color name to indexed value.

The ``multi_index`` file is an array that contains the string list of the colors as
they are defined in each ``multi_*`` array file.

The ``multi_intensity`` is an array that can be read or written to for the
individual color intensities.  All elements within this array must be written in
order for the color LED intensities to be updated.

Directory Layout Example
========================
.. code-block:: console

    root:/sys/class/leds/multicolor:status# ls -lR

Directory layout과 brightness 계산

예제 `/sys/class/leds/multicolor:status`에는 `brightness`, `max_brightness`, `multi_index`, `multi_intensity` 네 file이 있습니다.

각 color LED에 실제로 전달되는 brightness는 global brightness와 해당 color intensity를 곱하고 `max_brightness`로 나누어 계산합니다.

공식은 `led_brightness = brightness * multi_intensity / max_brightness`입니다. 따라서 `multi_intensity`가 hue 비율을 정하고 `brightness`가 비율을 보존하면서 전체 밝기를 scale합니다.

예제에서 `multi_index`는 `green blue red`이고 `multi_intensity`에 `43 226 138`을 씁니다. 이에 따라 green=43, blue=226, red=138이며 각 최대값은 255입니다.

    -rw-r--r--    1 root     root          4096 Oct 19 16:16 brightness
    -r--r--r--    1 root     root          4096 Oct 19 16:16 max_brightness
    -r--r--r--    1 root     root          4096 Oct 19 16:16 multi_index
    -rw-r--r--    1 root     root          4096 Oct 19 16:16 multi_intensity

..

Multicolor Class Brightness Control
===================================
The brightness level for each LED is calculated based on the color LED
intensity setting divided by the global max_brightness setting multiplied by
the requested brightness.

``led_brightness = brightness * multi_intensity/max_brightness``

Example:
A user first writes the multi_intensity file with the brightness levels
for each LED that are necessary to achieve a certain color output from a
multicolor LED group.

.. code-block:: console

    # cat /sys/class/leds/multicolor:status/multi_index
    green blue red

    # echo 43 226 138 > /sys/class/leds/multicolor:status/multi_intensity

    red -
            intensity = 138
            max_brightness = 255
    green -
            intensity = 43
            max_brightness = 255
    blue -
            intensity = 226
            max_brightness = 255

..

The user can control the brightness of that multicolor LED group by writing the
global 'brightness' control.  Assuming a max_brightness of 255 the user
may want to dim the LED color group to half.  The user would write a value of
128 to the global brightness file then the values written to each LED will be
adjusted base on this value.

Group dimming 예제

사용자는 global `brightness` file을 써서 multicolor LED group 전체 밝기를 제어합니다. `max_brightness=255`에서 절반 수준으로 낮추려면 `brightness`에 `128`을 씁니다.

Global `brightness`를 읽으면 group의 현재 밝기 값인 `128`을 반환합니다. `multi_intensity`의 색상 배합과 global `brightness`의 lightness 제어가 독립적이므로 dimming해도 hue가 유지됩니다.

.. code-block:: console

    # cat /sys/class/leds/multicolor:status/max_brightness
    255
    # echo 128 > /sys/class/leds/multicolor:status/brightness

..

.. code-block:: none

    adjusted_red_value = 128 * 138/255 = 69
    adjusted_green_value = 128 * 43/255 = 21
    adjusted_blue_value = 128 * 226/255 = 113

..

Reading the global brightness file will return the current brightness value of
the color LED group.

.. code-block:: console

    # cat /sys/class/leds/multicolor:status/brightness
    128

..