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Last Reviewed: 10/05/2007
WDT Watchdog Timer Interfaces For The Linux Operating System
Alan Cox <>
ICS WDT501-P (no fan tachometer)
All the 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
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.
The wdt card cannot be safely probed for. Instead you need to pass
wdt=ioaddr,irq as a boot parameter - eg "wdt=0x240,11".
Reboot Timer X X
External Reboot X X
I/O Port Monitor o o
Temperature X o
Fan Speed X o
Power Under X o
Power Over X o
Overheat X o
The external event interfaces on the WDT boards are not currently supported.
Minor numbers are however allocated for it.
Example Watchdog Driver: see Documentation/watchdog/src/watchdog-simple.c