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 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 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 ‘__’
                           ‘\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>.

Debian                                           April 24, 2007                                           LED(4)