LEDS(4)

NAME
leds - sun3 diagnostic Light Emitting Diodes driver

SYNOPSIS
#include <machine/leds.h>

DESCRIPTION
With the exception of the Sun 3/80, all sun3 machines are equipped a diagnostic display of eight Light Emitting Diodes (LEDs), located on the back of the system unit. The Sun 3/80 has a single LED, which is located on the front panel.

The kernel changes the display during periods of idle processor activity according to a stored sequential pattern list. The /dev/leds interface provides a way of manipulating the pattern list via simple file I/O.

The structure of the file is as follows:

    struct led_patterns {
            u_char divisor;
            u_char patlen;
            u_char pat[256];
    };

divisor
    The number of idle periods to wait before switching to the next pattern in the array.

patlen
    The number of patterns stored in the array.

pat The array of patterns to display.

When a clock interrupt occurs while the processor is idle, a pattern countdown timer is decremented. When the countdown timer reaches zero it is reset with the divisor value and the next pattern in the array is selected and displayed.

Each 8-bit pattern describes the state of the diagnostic LEDs. With the exception of the 3/80, a set bit in a pattern indicates that its corresponding LED should be extinguished, while a reset bit indicates an LED to be illuminated. On the 3/80 the polarity of the bits is reversed and only the lowest order bit is used.

FILES
/dev/leds

EXAMPLES
The following example uses awk(1) to display the repeating animation of a single lit LED scrolling from one end of the display to the other, using six clock ticks between each update.

# echo 5 8 254 253 251 247 239 223 191 127 | awk '{ for (i=1;iNF;i++) printf("%c",$i+0); }' /dev/leds

ERRORS
An I/O transfer to /dev/leds will complete successfully unless:

[EIO]
    A read or write starting beyond the end of the file was attempted.

SEE ALSO
ppt(6)

HISTORY
/dev/leds first appeared in NetBSD 1.2.