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