87 lines
3.0 KiB
ReStructuredText
87 lines
3.0 KiB
ReStructuredText
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.. SPDX-License-Identifier: GPL-2.0
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====================================
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Multicolor LED handling under Linux
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====================================
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Description
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===========
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The multicolor class groups monochrome LEDs and allows controlling two
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aspects of the final combined color: hue and lightness. The former is
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controlled via the multi_intensity array file and the latter is controlled
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via brightness file.
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Multicolor Class Control
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========================
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The multicolor class presents files that groups the colors as indexes in an
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array. These files are children under the LED parent node created by the
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led_class framework. The led_class framework is documented in led-class.rst
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within this documentation directory.
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Each colored LED will be indexed under the multi_* files. The order of the
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colors will be arbitrary. The multi_index file can be read to determine the
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color name to indexed value.
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The multi_index file is an array that contains the string list of the colors as
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they are defined in each multi_* array file.
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The multi_intensity is an array that can be read or written to for the
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individual color intensities. All elements within this array must be written in
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order for the color LED intensities to be updated.
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Directory Layout Example
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========================
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root:/sys/class/leds/multicolor:status# ls -lR
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-rw-r--r-- 1 root root 4096 Oct 19 16:16 brightness
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-r--r--r-- 1 root root 4096 Oct 19 16:16 max_brightness
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-r--r--r-- 1 root root 4096 Oct 19 16:16 multi_index
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-rw-r--r-- 1 root root 4096 Oct 19 16:16 multi_intensity
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Multicolor Class Brightness Control
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===================================
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The brightness level for each LED is calculated based on the color LED
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intensity setting divided by the global max_brightness setting multiplied by
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the requested brightness.
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led_brightness = brightness * multi_intensity/max_brightness
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Example:
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A user first writes the multi_intensity file with the brightness levels
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for each LED that are necessary to achieve a certain color output from a
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multicolor LED group.
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cat /sys/class/leds/multicolor:status/multi_index
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green blue red
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echo 43 226 138 > /sys/class/leds/multicolor:status/multi_intensity
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red -
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intensity = 138
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max_brightness = 255
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green -
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intensity = 43
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max_brightness = 255
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blue -
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intensity = 226
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max_brightness = 255
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The user can control the brightness of that multicolor LED group by writing the
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global 'brightness' control. Assuming a max_brightness of 255 the user
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may want to dim the LED color group to half. The user would write a value of
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128 to the global brightness file then the values written to each LED will be
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adjusted base on this value.
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cat /sys/class/leds/multicolor:status/max_brightness
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255
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echo 128 > /sys/class/leds/multicolor:status/brightness
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adjusted_red_value = 128 * 138/255 = 69
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adjusted_green_value = 128 * 43/255 = 21
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adjusted_blue_value = 128 * 226/255 = 113
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Reading the global brightness file will return the current brightness value of
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the color LED group.
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cat /sys/class/leds/multicolor:status/brightness
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128
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