1 .. SPDX-License-Identifier: GPL-2.0 2 3 ==================================== 4 Multicolor LED handling under Linux 5 ==================================== 6 7 Description 8 =========== 9 The multicolor class groups monochrome LEDs and allows controlling two 10 aspects of the final combined color: hue and lightness. The former is 11 controlled via the multi_intensity array file and the latter is controlled 12 via brightness file. 13 14 Multicolor Class Control 15 ======================== 16 The multicolor class presents files that groups the colors as indexes in an 17 array. These files are children under the LED parent node created by the 18 led_class framework. The led_class framework is documented in led-class.rst 19 within this documentation directory. 20 21 Each colored LED will be indexed under the multi_* files. The order of the 22 colors will be arbitrary. The multi_index file can be read to determine the 23 color name to indexed value. 24 25 The multi_index file is an array that contains the string list of the colors as 26 they are defined in each multi_* array file. 27 28 The multi_intensity is an array that can be read or written to for the 29 individual color intensities. All elements within this array must be written in 30 order for the color LED intensities to be updated. 31 32 Directory Layout Example 33 ======================== 34 root:/sys/class/leds/multicolor:status# ls -lR 35 -rw-r--r-- 1 root root 4096 Oct 19 16:16 brightness 36 -r--r--r-- 1 root root 4096 Oct 19 16:16 max_brightness 37 -r--r--r-- 1 root root 4096 Oct 19 16:16 multi_index 38 -rw-r--r-- 1 root root 4096 Oct 19 16:16 multi_intensity 39 40 Multicolor Class Brightness Control 41 =================================== 42 The brightness level for each LED is calculated based on the color LED 43 intensity setting divided by the global max_brightness setting multiplied by 44 the requested brightness. 45 46 led_brightness = brightness * multi_intensity/max_brightness 47 48 Example: 49 A user first writes the multi_intensity file with the brightness levels 50 for each LED that are necessary to achieve a certain color output from a 51 multicolor LED group. 52 53 cat /sys/class/leds/multicolor:status/multi_index 54 green blue red 55 56 echo 43 226 138 > /sys/class/leds/multicolor:status/multi_intensity 57 58 red - 59 intensity = 138 60 max_brightness = 255 61 green - 62 intensity = 43 63 max_brightness = 255 64 blue - 65 intensity = 226 66 max_brightness = 255 67 68 The user can control the brightness of that multicolor LED group by writing the 69 global 'brightness' control. Assuming a max_brightness of 255 the user 70 may want to dim the LED color group to half. The user would write a value of 71 128 to the global brightness file then the values written to each LED will be 72 adjusted base on this value. 73 74 cat /sys/class/leds/multicolor:status/max_brightness 75 255 76 echo 128 > /sys/class/leds/multicolor:status/brightness 77 78 adjusted_red_value = 128 * 138/255 = 69 79 adjusted_green_value = 128 * 43/255 = 21 80 adjusted_blue_value = 128 * 226/255 = 113 81 82 Reading the global brightness file will return the current brightness value of 83 the color LED group. 84 85 cat /sys/class/leds/multicolor:status/brightness 86 128
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