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LED(4)			     Kernel Interfaces Manual			  LED(4)

NAME
     led -- API for manipulating LED's, lamps and other annunciators

SYNOPSIS
     #include <dev/led/led.h>

     typedef void led_t(void *priv, int onoff);

     struct cdev *
     led_create_state(led_t *func, void *priv, char const *name, int state);

     struct cdev *
     led_create(led_t *func, void *priv, char const *name);

     void
     led_destroy(struct cdev *);

DESCRIPTION
     The  led driver provides generic support for handling LEDs, lamps and other
     annunciators.

     The hardware driver must supply a function to turn the annunciator  on  and
     off and the device name of the annunciator relative to /dev/led/.	The priv
     argument is passed back to this on/off function and can be used however the
     hardware driver sees fit.

     The  lamp	can  be  controlled  by opening and writing ASCII strings to the
     /dev/led/bla device.

     In the following, we will use this special notation to indicate the result-
     ing output of the annunciator:

	   *	   The annunciator is on for 1/10th second.
	   _	   The annunciator is off for 1/10th second.

     State can be set directly, and since the change happens immediately, it  is
     possible  to  flash the annunciator with very short periods and synchronize
     it with program events.  It should be noted that  there  is  a  non-trivial
     overhead, so this may not be usable for benchmarking or measuring short in-
     tervals.

	   0	   Turn the annunciator off immediately.
	   1	   Turn the annunciator on immediately.

     Flashing can be set with a given period.  The pattern continues endlessly.

	   f	   _*
	   f1	   _*
	   f2	   __**
	   f3	   ___***
	   ...
	   f9	   _________*********

     Three high-level commands are available:

	   d%d	   Numbers.  Each digit is blinked out at 1/10th second, zero as
		   ten	pulses.  Between digits a one second pause and after the
		   last digit a two second pause after which the sequence is re-
		   peated.

	   s%s	   String.  This gives full control over the annunciator.   Let-
		   ters  `A'  ... `J' turn the annunciator on for from 1/10th to
		   one full second.  Letters `a' ... `j'  turn	the  annunciator
		   off	for 1/10th to one full second.	Letters `u' and `U' turn
		   the annunciator off and on respectively  when  the  next  UTC
		   second starts.  Unless terminated with a `.', the sequence is
		   immediately repeated.

	   m%s	   Morse.

			 `.'	 becomes `_*'
			 `-'	 becomes `_***'
			 ` '	 becomes `__'
			 `\n'	 becomes `____'

     The sequence is repeated after a one second pause.

FILES
     /dev/led/*

EXAMPLES
     A `d12' flashes the lamp

	   *__________*_*______________________________

     A `sAaAbBa' flashes

	   *_*__**_

     /usr/bin/morse -l "Soekris rocks" > /dev/led/error

SEE ALSO
     morse(6)

HISTORY
     The led driver first appeared in FreeBSD 5.2.

AUTHORS
     This software was written by Poul-Henning Kamp <phk@FreeBSD.org>.

     This  manual  page  was  written  by Sergey A. Osokin <osa@FreeBSD.org> and
     Poul-Henning Kamp <phk@FreeBSD.org>.

FreeBSD ports 15.1		 April 24, 2007 			  LED(4)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=led&sektion=4&manpath=FreeBSD+15.1-RELEASE+and+Ports>

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