[GitHub/mt8127/android_kernel_alcatel_ttab.git] / Documentation / watchdog / wdt.txt

Last Reviewed: 10/05/2007

	WDT Watchdog Timer Interfaces For The Linux Operating System
		Alan Cox <alan@lxorguk.ukuu.org.uk>

	ICS	WDT501-P
	ICS	WDT501-P (no fan tachometer)
	ICS	WDT500-P

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 ICS ISA-bus wdt card cannot be safely probed for. Instead you need to
pass IO address and IRQ boot parameters.  E.g.:
	wdt.io=0x240 wdt.irq=11

Other "wdt" driver parameters are:
	heartbeat	Watchdog heartbeat in seconds (default 60)
	nowayout	Watchdog cannot be stopped once started (kernel
				build parameter)
	tachometer	WDT501-P Fan Tachometer support (0=disable, default=0)
	type		WDT501-P Card type (500 or 501, default=500)

Features
--------
		WDT501P		WDT500P
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
Commit	Line	Data
4d389dce AC	1	Last 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
	10	All the interfaces provide /dev/watchdog, which when open must be written
	11	to within a timeout or the machine will reboot. Each write delays the reboot
	12	time another timeout. In the case of the software watchdog the ability to
	13	reboot will depend on the state of the machines and interrupts. The hardware
	14	boards physically pull the machine down off their own onboard timers and
	15	will reboot from almost anything.
	16
4724ba57	17	A second temperature monitoring interface is available on the WDT501P cards.
4d389dce AC	18	This provides /dev/temperature. This is the machine internal temperature in
	19	degrees Fahrenheit. Each read returns a single byte giving the temperature.
	20
	21	The third interface logs kernel messages on additional alert events.
	22
4724ba57 RD	23	The ICS ISA-bus wdt card cannot be safely probed for. Instead you need to
	24	pass IO address and IRQ boot parameters. E.g.:
	25	wdt.io=0x240 wdt.irq=11
	26
	27	Other "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)
4d389dce AC	33
	34	Features
	35	--------
	36	WDT501P WDT500P
	37	Reboot Timer X X
	38	External Reboot X X
	39	I/O Port Monitor o o
	40	Temperature X o
	41	Fan Speed X o
	42	Power Under X o
	43	Power Over X o
	44	Overheat X o
	45
	46	The external event interfaces on the WDT boards are not currently supported.
	47	Minor numbers are however allocated for it.
	48
	49
	50	Example Watchdog Driver: see Documentation/watchdog/src/watchdog-simple.c