projects / deliverable / linux.git / blame
| Commit | Line | Data |
|---|---|---|
| 5e417281 FB |
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 |