linux/Documentation/watchdog/wdt.txt
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   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 ICS ISA-bus wdt card cannot be safely probed for. Instead you need to
  24pass IO address and IRQ boot parameters.  E.g.:
  25        wdt.io=0x240 wdt.irq=11
  26
  27Other "wdt" driver parameters are:
  28        heartbeat       Watchdog heartbeat in seconds (default 60)
  29        nowayout        Watchdog cannot be stopped once started (kernel
  30                                build parameter)
  31        tachometer      WDT501-P Fan Tachometer support (0=disable, default=0)
  32        type            WDT501-P Card type (500 or 501, default=500)
  33
  34Features
  35--------
  36                WDT501P         WDT500P
  37Reboot Timer       X               X
  38External Reboot    X               X
  39I/O Port Monitor   o               o
  40Temperature        X               o
  41Fan Speed          X               o
  42Power Under        X               o
  43Power Over         X               o
  44Overheat           X               o
  45
  46The external event interfaces on the WDT boards are not currently supported.
  47Minor numbers are however allocated for it.
  48
  49
  50Example Watchdog Driver:  see Documentation/watchdog/src/watchdog-simple.c
  51
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