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



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


      #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);
      led_destroy(struct cdev *);


      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 how‐
      ever 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 synchro‐
      nize 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 end‐
            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 annuncia‐
                    tor 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.




      A ‘d12’ flashes the lamp
      A ‘sAaAbBa’ flashes
      /usr/games/morse -l "Soekris rocks" > /dev/led/error


      The led driver first appeared in FreeBSD 5.2.


      This software was written by Poul-Henning Kamp 〈〉.
      This manual page was written by Sergey A. Osokin 〈〉 and
      Poul-Henning Kamp 〈〉.


Based on BSD UNIX
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