path: root/Documentation/leds/ledtrig-oneshot.txt
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authorAnton Arapov <>2012-10-29 11:15:37 +0100
committerAnton Arapov <>2012-10-29 11:15:37 +0100
commit7d558cd9c7b18e4b16953265aa0da45e63f3b968 (patch)
tree7135d5a810768c9c619346282ee9cfdf1765e225 /Documentation/leds/ledtrig-oneshot.txt
parent985ef6b2108ed28ffd5f6630e1e0fce2e2a775f2 (diff)
fedora kernel: cd394142aac30b5c751f25b517572e2448695641v3.6.3-2f17
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+One-shot LED Trigger
+This is a LED trigger useful for signaling the user of an event where there are
+no clear trap points to put standard led-on and led-off settings. Using this
+trigger, the application needs only to signal the trigger when an event has
+happened, than the trigger turns the LED on and than keeps it off for a
+specified amount of time.
+This trigger is meant to be usable both for sporadic and dense events. In the
+first case, the trigger produces a clear single controlled blink for each
+event, while in the latter it keeps blinking at constant rate, as to signal
+that the events are arriving continuously.
+A one-shot LED only stays in a constant state when there are no events. An
+additional "invert" property specifies if the LED has to stay off (normal) or
+on (inverted) when not rearmed.
+The trigger can be activated from user space on led class devices as shown
+ echo oneshot > trigger
+This adds the following sysfs attributes to the LED:
+ delay_on - specifies for how many milliseconds the LED has to stay at
+ LED_FULL brightness after it has been armed.
+ Default to 100 ms.
+ delay_off - specifies for how many milliseconds the LED has to stay at
+ LED_OFF brightness after it has been armed.
+ Default to 100 ms.
+ invert - reverse the blink logic. If set to 0 (default) blink on for delay_on
+ ms, then blink off for delay_off ms, leaving the LED normally off. If
+ set to 1, blink off for delay_off ms, then blink on for delay_on ms,
+ leaving the LED normally on.
+ Setting this value also immediately change the LED state.
+ shot - write any non-empty string to signal an events, this starts a blink
+ sequence if not already running.
+Example use-case: network devices, initialization:
+ echo oneshot > trigger # set trigger for this led
+ echo 33 > delay_on # blink at 1 / (33 + 33) Hz on continuous traffic
+ echo 33 > delay_off
+interface goes up:
+ echo 1 > invert # set led as normally-on, turn the led on
+packet received/transmitted:
+ echo 1 > shot # led starts blinking, ignored if already blinking
+interface goes down
+ echo 0 > invert # set led as normally-off, turn the led off