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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
- below:
- 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
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