Based on kernel version 3.16. Page generated on 2014-08-06 21:40 EST.
1 One-shot LED Trigger 2 ==================== 3 4 This is a LED trigger useful for signaling the user of an event where there are 5 no clear trap points to put standard led-on and led-off settings. Using this 6 trigger, the application needs only to signal the trigger when an event has 7 happened, than the trigger turns the LED on and than keeps it off for a 8 specified amount of time. 9 10 This trigger is meant to be usable both for sporadic and dense events. In the 11 first case, the trigger produces a clear single controlled blink for each 12 event, while in the latter it keeps blinking at constant rate, as to signal 13 that the events are arriving continuously. 14 15 A one-shot LED only stays in a constant state when there are no events. An 16 additional "invert" property specifies if the LED has to stay off (normal) or 17 on (inverted) when not rearmed. 18 19 The trigger can be activated from user space on led class devices as shown 20 below: 21 22 echo oneshot > trigger 23 24 This adds the following sysfs attributes to the LED: 25 26 delay_on - specifies for how many milliseconds the LED has to stay at 27 LED_FULL brightness after it has been armed. 28 Default to 100 ms. 29 30 delay_off - specifies for how many milliseconds the LED has to stay at 31 LED_OFF brightness after it has been armed. 32 Default to 100 ms. 33 34 invert - reverse the blink logic. If set to 0 (default) blink on for delay_on 35 ms, then blink off for delay_off ms, leaving the LED normally off. If 36 set to 1, blink off for delay_off ms, then blink on for delay_on ms, 37 leaving the LED normally on. 38 Setting this value also immediately change the LED state. 39 40 shot - write any non-empty string to signal an events, this starts a blink 41 sequence if not already running. 42 43 Example use-case: network devices, initialization: 44 45 echo oneshot > trigger # set trigger for this led 46 echo 33 > delay_on # blink at 1 / (33 + 33) Hz on continuous traffic 47 echo 33 > delay_off 48 49 interface goes up: 50 51 echo 1 > invert # set led as normally-on, turn the led on 52 53 packet received/transmitted: 54 55 echo 1 > shot # led starts blinking, ignored if already blinking 56 57 interface goes down 58 59 echo 0 > invert # set led as normally-off, turn the led off