.\"	$NetBSD: leds.4,v 1.9.56.1 2019/09/02 16:39:24 martin Exp $
.\"
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.\" by der Mouse and Jeremy Cooper.
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.Dd March 2, 1996
.Dt LEDS 4 sun2
.Os
.Sh NAME
.Nm leds
.Nd sun2 diagnostic Light Emitting Diodes driver
.Sh SYNOPSIS
.In machine/leds.h
.Sh DESCRIPTION
All sun2 machines are equipped
a diagnostic display of eight Light Emitting Diodes (LEDs), located
on either the front (deskside chassis) or the back (desktop machine)
of the system unit.
.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.
A set bit in a pattern indicates that its
corresponding LED should be extinguished,
while a reset bit indicates an LED to be illuminated.
.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 .