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8dab9197 | 1 | ==================== |
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2 | One-shot LED Trigger |
3 | ==================== | |
4 | ||
5 | This is a LED trigger useful for signaling the user of an event where there are | |
6 | no clear trap points to put standard led-on and led-off settings. Using this | |
7 | trigger, the application needs only to signal the trigger when an event has | |
57fbfb3b | 8 | happened, then the trigger turns the LED on and then keeps it off for a |
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9 | specified amount of time. |
10 | ||
11 | This trigger is meant to be usable both for sporadic and dense events. In the | |
12 | first case, the trigger produces a clear single controlled blink for each | |
13 | event, while in the latter it keeps blinking at constant rate, as to signal | |
14 | that the events are arriving continuously. | |
15 | ||
16 | A one-shot LED only stays in a constant state when there are no events. An | |
17 | additional "invert" property specifies if the LED has to stay off (normal) or | |
18 | on (inverted) when not rearmed. | |
19 | ||
20 | The trigger can be activated from user space on led class devices as shown | |
8dab9197 | 21 | below:: |
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22 | |
23 | echo oneshot > trigger | |
24 | ||
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25 | This adds sysfs attributes to the LED that are documented in: |
26 | Documentation/ABI/testing/sysfs-class-led-trigger-oneshot | |
5e417281 | 27 | |
8dab9197 | 28 | Example use-case: network devices, initialization:: |
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29 | |
30 | echo oneshot > trigger # set trigger for this led | |
31 | echo 33 > delay_on # blink at 1 / (33 + 33) Hz on continuous traffic | |
32 | echo 33 > delay_off | |
33 | ||
8dab9197 | 34 | interface goes up:: |
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35 | |
36 | echo 1 > invert # set led as normally-on, turn the led on | |
37 | ||
8dab9197 | 38 | packet received/transmitted:: |
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39 | |
40 | echo 1 > shot # led starts blinking, ignored if already blinking | |
41 | ||
8dab9197 | 42 | interface goes down:: |
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43 | |
44 | echo 0 > invert # set led as normally-off, turn the led off |