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0001 ============================================================
0002 WDT Watchdog Timer Interfaces For The Linux Operating System
0003 ============================================================
0004 
0005 Last Reviewed: 10/05/2007
0006 
0007 Alan Cox <alan@lxorguk.ukuu.org.uk>
0008 
0009         - ICS   WDT501-P
0010         - ICS   WDT501-P (no fan tachometer)
0011         - ICS   WDT500-P
0012 
0013 All the interfaces provide /dev/watchdog, which when open must be written
0014 to within a timeout or the machine will reboot. Each write delays the reboot
0015 time another timeout. In the case of the software watchdog the ability to
0016 reboot will depend on the state of the machines and interrupts. The hardware
0017 boards physically pull the machine down off their own onboard timers and
0018 will reboot from almost anything.
0019 
0020 A second temperature monitoring interface is available on the WDT501P cards.
0021 This provides /dev/temperature. This is the machine internal temperature in
0022 degrees Fahrenheit. Each read returns a single byte giving the temperature.
0023 
0024 The third interface logs kernel messages on additional alert events.
0025 
0026 The ICS ISA-bus wdt card cannot be safely probed for. Instead you need to
0027 pass IO address and IRQ boot parameters.  E.g.::
0028 
0029         wdt.io=0x240 wdt.irq=11
0030 
0031 Other "wdt" driver parameters are:
0032 
0033         ===========     ======================================================
0034         heartbeat       Watchdog heartbeat in seconds (default 60)
0035         nowayout        Watchdog cannot be stopped once started (kernel
0036                         build parameter)
0037         tachometer      WDT501-P Fan Tachometer support (0=disable, default=0)
0038         type            WDT501-P Card type (500 or 501, default=500)
0039         ===========     ======================================================
0040 
0041 Features
0042 --------
0043 
0044 ================   =======         =======
0045                    WDT501P         WDT500P
0046 ================   =======         =======
0047 Reboot Timer       X               X
0048 External Reboot    X               X
0049 I/O Port Monitor   o               o
0050 Temperature        X               o
0051 Fan Speed          X               o
0052 Power Under        X               o
0053 Power Over         X               o
0054 Overheat           X               o
0055 ================   =======         =======
0056 
0057 The external event interfaces on the WDT boards are not currently supported.
0058 Minor numbers are however allocated for it.
0059 
0060 
0061 Example Watchdog Driver:
0062 
0063         see samples/watchdog/watchdog-simple.c