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