	Watchdog Timer Interfaces For The Linux Operating System

		Alan Cox <alan@lxorguk.ukuu.org.uk>

	    Custom Linux Driver And Program Development


The following watchdog drivers are currently implemented:

	IMS	WDT501-P
	INS	WDT501-P (no fan tachometer)
	IMS	WDT500-P
	Software Only

All four interfaces provide /dev/watchdog, which when open must be written
to within a minute or the machine will reboot. Each write delays the reboot
time another minute. In the case of the software watchdog the ability to 
reboot will depend on the state of the machines and interrupts. The hardware
boards physically pull the machine down off their own onboard timers and
will reboot from almost anything.

A second temperature monitoring interface is available on the WDT501P cards
and provides /dev/temperature. This is the machine internal temperature in
degrees farenheit. Each read returns a single byte giving the temperature.

The third interface logs kernel messages on additional alert events.

At the moment only the software watchdog is available in the standard
kernel.

Features
--------
		WDT501P		WDT500P		Software
Reboot Timer	   X               X                X
External Reboot	   X	           X                o
Temperature	   X		   o		    o
Fan Speed          X		   o		    o
Power Under	   X               o                o
Power Over         X               o                o
Overheat           X               o                o

The external event interfaces on the WDT boards are not currently supported.


Example Watchdog Driver
-----------------------

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>

int main(int argc, const char *argv[])
{
	int fd=open("/dev/watchdog",O_WRONLY);
	if(fd==-1)
	{
		perror("watchdog");
		exit(1);
	}
	while(1)
	{
		write(fd,"\0",1);
		sleep(10);
	}
}


