/Documentation/watchdog/wdt.txt

 1Last Reviewed: 10/05/2007
 2
 3	WDT Watchdog Timer Interfaces For The Linux Operating System
 4		Alan Cox <alan@lxorguk.ukuu.org.uk>
 5
 6	ICS	WDT501-P
 7	ICS	WDT501-P (no fan tachometer)
 8	ICS	WDT500-P
 9
10All the interfaces provide /dev/watchdog, which when open must be written
11to within a timeout or the machine will reboot. Each write delays the reboot
12time another timeout. In the case of the software watchdog the ability to
13reboot will depend on the state of the machines and interrupts. The hardware
14boards physically pull the machine down off their own onboard timers and
15will reboot from almost anything.
16
17A second temperature monitoring interface is available on the WDT501P cards
18This provides /dev/temperature. This is the machine internal temperature in
19degrees Fahrenheit. Each read returns a single byte giving the temperature.
20
21The third interface logs kernel messages on additional alert events.
22
23The wdt card cannot be safely probed for. Instead you need to pass
24wdt=ioaddr,irq as a boot parameter - eg "wdt=0x240,11".
25
26Features
27--------
28		WDT501P		WDT500P
29Reboot Timer	   X               X
30External Reboot	   X	           X
31I/O Port Monitor   o		   o
32Temperature	   X		   o
33Fan Speed          X		   o
34Power Under	   X               o
35Power Over         X               o
36Overheat           X               o
37
38The external event interfaces on the WDT boards are not currently supported.
39Minor numbers are however allocated for it.
40
41
42Example Watchdog Driver:  see Documentation/watchdog/src/watchdog-simple.c
43