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