.\" Copyright (c) 1998,1999 Alex Nash
.\" All rights reserved.
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.\"	$OpenBSD: wdt.4,v 1.3 2001/08/02 20:37:35 hugh Exp $
.\"
.Dd April 25, 1999
.Dt WDT 4 i386
.Os
.Sh NAME
.Nm wdt
.Nd ICS PCI-WDT500/501 watchdog timer device driver
.Sh SYNOPSIS
.Cd option WDT_DISABLE_BUZZER
.Cd wdt0 at pci? dev ? function ?
.Sh DESCRIPTION
The
.Nm
driver provides support for the Industrial Computer Source
PCI-WDT500 and PCI-WDT501 boards.
.Pp
For PCI-WDT500 boards, basic watchdog timer functionality is supported.
For PCI-WDT501 boards, additional access to the onboard buzzer,
isolated inputs, temperature, and power supply monitors is provided.
To disable the onboard buzzer on PCI-WDT501 boards, add
.Ic option WDT_DISABLE_BUZZER
to your kernel configuration.
.Pp
By default the watchdog timer is set to 30 seconds and is refreshed
by the kernel's timeout processing.
If the kernel crashes, the watchdog
timer is not reset and the system will reboot (assuming a proper connection
is made between the WDT50x and motherboard).
Alternatively, the watchdog
can be reinitialized via a userland process which ensures that process
scheduling, not just kernel timeout processing, is still taking place.
See the
.Dv WIOCSCHED
.Xr ioctl 2
below for more information.
.Sh INTERFACE
The
.Nm
driver is controlled via
.Xr ioctl 2
calls to
.Pa /dev/wdt0 .
The following commands are supported:
.Bl -tag -width WIOCGETSTATE
.It Dv WIOCGETSTATE
Returns the current temperature and board status into the
wdt_state structure pointer passed to
.Xr ioctl 2 .
See
.Aq Pa dev/pci/wdt50x.h
for the definition of the wdt_state structure and state bits.
.It Dv WIOCSCHED
Places the process into an infinite loop (interrupted only via a signal)
to guarantee process scheduling.
The driver utilizes the process' context to reinitialize the watchdog timeout.
Should process scheduling fail, the timeout will not be reinitialized and the
system will be rebooted.
Note that it is possible to force a reboot by sending a
.Dv SIGSTOP
signal to a process in
.Dv WIOCSCHED
and waiting for the watchdog timer to expire.
Since
.Dv WIOCSCHED
can have such dramatic consequences, it may only be issued by superuser
processes regardless of the permissions on
.Pa /dev/wdt0 .
.El
.Sh FILES
.Bl -tag -width /usr/include/dev/pci/wdt50x.h -compact
.It Pa /dev/wdt0
watchdog control device
.It Pa /usr/include/dev/pci/wdt50x.h
structure and ioctl definitions
.El
.Sh SEE ALSO
.Xr ioctl 2
.Sh HISTORY
The
.Nm
driver first appeared in
.Ox 2.6 .
.Sh BUGS
The ioctl interface isn't generic.
.Pp
It's unwise to combine
.Nm
with
.Xr ddb 4
since the latter may prevent the former from resetting the
watchdog timeout before it expires.