mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-12-25 12:04:46 +08:00
5e417281cd
Add oneshot trigger to blink a led with configurale parameters via sysfs. Signed-off-by: Fabio Baltieri <fabio.baltieri@gmail.com> Cc: Shuah Khan <shuahkhan@gmail.com> Signed-off-by: Bryan Wu <bryan.wu@canonical.com>
60 lines
2.2 KiB
Plaintext
60 lines
2.2 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 the following sysfs attributes to the LED:
|
|
|
|
delay_on - specifies for how many milliseconds the LED has to stay at
|
|
LED_FULL brightness after it has been armed.
|
|
Default to 100 ms.
|
|
|
|
delay_off - specifies for how many milliseconds the LED has to stay at
|
|
LED_OFF brightness after it has been armed.
|
|
Default to 100 ms.
|
|
|
|
invert - reverse the blink logic. If set to 0 (default) blink on for delay_on
|
|
ms, then blink off for delay_off ms, leaving the LED normally off. If
|
|
set to 1, blink off for delay_off ms, then blink on for delay_on ms,
|
|
leaving the LED normally on.
|
|
Setting this value also immediately change the LED state.
|
|
|
|
shot - write any non-empty string to signal an events, this starts a blink
|
|
sequence if not already running.
|
|
|
|
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
|