LED(4)							   BSD 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 resulting 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 syn-
     chronize it with program events.  It should be noted that there is a non-trivial overhead, so this may not be usable for benchmarking or mea-
     suring short intervals.

	   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 repeated.

	   s%s	   String.  This gives full control over the annunciator.  Letters '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 '__'
			 '
'	 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>.

BSD
								  April 24, 2007							       BSD