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sysfs-class-led-trigger-pattern
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sysfs-class-led-trigger-pattern
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What: /sys/class/leds/<led>/pattern
Date: September 2018
KernelVersion: 4.20
Description:
Specify a software pattern for the LED, that supports altering
the brightness for the specified duration with one software
timer. It can do gradual dimming and step change of brightness.
The pattern is given by a series of tuples, of brightness and
duration (ms). The LED is expected to traverse the series and
each brightness value for the specified duration. Duration of
0 means brightness should immediately change to new value, and
writing malformed pattern deactivates any active one.
1. For gradual dimming, the dimming interval now is set as 50
milliseconds. So the tuple with duration less than dimming
interval (50ms) is treated as a step change of brightness,
i.e. the subsequent brightness will be applied without adding
intervening dimming intervals.
The gradual dimming format of the software pattern values should be:
"brightness_1 duration_1 brightness_2 duration_2 brightness_3
duration_3 ...". For example:
echo 0 1000 255 2000 > pattern
It will make the LED go gradually from zero-intensity to max (255)
intensity in 1000 milliseconds, then back to zero intensity in 2000
milliseconds:
LED brightness
^
255-| / \ / \ /
| / \ / \ /
| / \ / \ /
| / \ / \ /
0-| / \/ \/
+---0----1----2----3----4----5----6------------> time (s)
2. To make the LED go instantly from one brigntess value to another,
we should use use zero-time lengths (the brightness must be same as
the previous tuple's). So the format should be:
"brightness_1 duration_1 brightness_1 0 brightness_2 duration_2
brightness_2 0 ...". For example:
echo 0 1000 0 0 255 2000 255 0 > pattern
It will make the LED stay off for one second, then stay at max brightness
for two seconds:
LED brightness
^
255-| +---------+ +---------+
| | | | |
| | | | |
| | | | |
0-| -----+ +----+ +----
+---0----1----2----3----4----5----6------------> time (s)
What: /sys/class/leds/<led>/hw_pattern
Date: September 2018
KernelVersion: 4.20
Description:
Specify a hardware pattern for the LED, for LED hardware that
supports autonomously controlling brightness over time, according
to some preprogrammed hardware patterns. It deactivates any active
software pattern.
Since different LED hardware can have different semantics of
hardware patterns, each driver is expected to provide its own
description for the hardware patterns in their ABI documentation
file.
What: /sys/class/leds/<led>/repeat
Date: September 2018
KernelVersion: 4.20
Description:
Specify a pattern repeat number. -1 means repeat indefinitely,
other negative numbers and number 0 are invalid.
This file will always return the originally written repeat
number.