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+        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:
+
+        ICS     WDT501-P
+        ICS     WDT501-P (no fan tachometer)
+        ICS     WDT500-P
+        Software Only
+        SA1100 Internal Watchdog
+        Berkshire Products PC Watchdog Revision A & C (by Ken Hollis)
+
+
+All six interfaces provide /dev/watchdog, which when open must be written
+to within a timeout or the machine will reboot. Each write delays the reboot
+time another timeout. 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 some Berkshire cards. This provides /dev/temperature. This is the machine 
+internal temperature in degrees Fahrenheit. Each read returns a single byte 
+giving the temperature.
+
+The third interface logs kernel messages on additional alert events.
+
+Both software and hardware watchdog drivers are available in the standard
+kernel. If you are using the software watchdog, you probably also want
+to use "panic=60" as a boot argument as well.
+
+The wdt card cannot be safely probed for. Instead you need to pass
+wdt=ioaddr,irq as a boot parameter - eg "wdt=0x240,11".
+
+The SA1100 watchdog module can be configured with the "sa1100_margin"
+commandline argument which specifies timeout value in seconds.
+
+The i810 TCO watchdog modules can be configured with the "i810_margin"
+commandline argument which specifies the counter initial value. The counter
+is decremented every 0.6 seconds and default to 50 (30 seconds). Values can
+range between 3 and 63.
+
+The i810 TCO watchdog driver also implements the WDIOC_GETSTATUS and
+WDIOC_GETBOOTSTATUS ioctl()s. WDIOC_GETSTATUS returns the actual counter value
+and WDIOC_GETBOOTSTATUS returns the value of TCO2 Status Register (see Intel's
+documentation for the 82801AA and 82801AB datasheet). 
+
+Features
+--------
+                WDT501P         WDT500P         Software        Berkshire       i810 TCO        SA1100WD
+Reboot Timer       X               X                X               X               X               X
+External Reboot    X               X                o               o               o               X
+I/O Port Monitor   o               o                o               X               o               o
+Temperature        X               o                o               X               o               o
+Fan Speed          X               o                o               o               o               o
+Power Under        X               o                o               o               o               o
+Power Over         X               o                o               o               o               o
+Overheat           X               o                o               o               o               o
+
+The external event interfaces on the WDT boards are not currently supported.
+Minor numbers are however allocated for it.
+
+
+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);
+                fsync(fd);
+                sleep(10);
+        }
+}
+
+
+Contact Information
+
+People keep asking about the WDT watchdog timer hardware: The phone contacts
+for Industrial Computer Source are:
+ 
+Industrial Computer Source
+http://www.indcompsrc.com
+ICS Advent, San Diego
+6260 Sequence Dr.
+San Diego, CA 92121-4371
+Phone (858) 677-0877
+FAX: (858) 677-0895
+>
+ICS Advent Europe, UK
+Oving Road
+Chichester,
+West Sussex,
+PO19 4ET, UK
+Phone: 00.44.1243.533900
+
+
+and please mention Linux when enquiring.
+
+For full information about the PCWD cards see the pcwd-watchdog.txt document.