.\"	$NetBSD: leds.4,v 1.13 2017/07/03 21:30:59 wiz Exp $
.\"
.\" Copyright (c) 1997 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by der Mouse and Jeremy Cooper.
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.Dd March 2, 1996
.Dt LEDS 4 sun3
.Os
.Sh NAME
.Nm leds
.Nd sun3 diagnostic Light Emitting Diodes driver
.Sh SYNOPSIS
.In machine/leds.h
.Sh 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.
.Pp
The kernel changes the display during periods of idle processor activity
according to a stored sequential pattern list.
The
.Pa /dev/leds
interface provides a way of manipulating the pattern list via simple file I/O.
.Pp
The structure of the file is as follows:
.Bd -literal
struct led_patterns {
        u_char divisor;
        u_char patlen;
        u_char pat[256];
};
.Ed
.Bl -tag -width divisor
.It Sy divisor
The number of idle periods to wait before switching to the next pattern in
the array.
.It Sy patlen
The number of patterns stored in the array.
.It Sy pat
The array of patterns to display.
.El
.Pp
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
.Sy divisor
value and the next pattern in the array is selected and displayed.
.Pp
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.
.Sh FILES
.Bl -tag -width /dev/leds -compact
.It Pa /dev/leds
.El
.Sh EXAMPLES
The following example uses
.Xr 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.
.Bd -ragged -offset indent
# echo 5 8 254 253 251 247 239 223 191 127 |
  awk '{ for (i=1;i\*[Le]NF;i++) printf("%c",$i+0); }' > /dev/leds
.Ed
.Sh ERRORS
An I/O transfer to
.Pa /dev/leds
will complete successfully unless:
.Bl -tag -width Er
.It Bq Er EIO
A read or write starting beyond the end of the file was attempted.
.El
.Sh SEE ALSO
.Xr ppt 6
.Sh HISTORY
.Pa /dev/leds
first appeared in
.Nx 1.2 .