44 lines
1.5 KiB
Plaintext
44 lines
1.5 KiB
Plaintext
|
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 sysfs attributes to the LED that are documented in:
|
||
|
|
Documentation/ABI/testing/sysfs-class-led-trigger-oneshot
|
||
|
|
|
||
|
|
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
|