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phoenix |
Watchdog Timer Interfaces For The Linux Operating System
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Alan Cox
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Custom Linux Driver And Program Development
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The following watchdog drivers are currently implemented:
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ICS WDT501-P
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ICS WDT501-P (no fan tachometer)
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ICS WDT500-P
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Software Only
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SA1100 Internal Watchdog
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Berkshire Products PC Watchdog Revision A & C (by Ken Hollis)
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All six interfaces provide /dev/watchdog, which when open must be written
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to within a timeout or the machine will reboot. Each write delays the reboot
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time another timeout. In the case of the software watchdog the ability to
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reboot will depend on the state of the machines and interrupts. The hardware
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boards physically pull the machine down off their own onboard timers and
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will reboot from almost anything.
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A second temperature monitoring interface is available on the WDT501P cards
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and some Berkshire cards. This provides /dev/temperature. This is the machine
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internal temperature in degrees Fahrenheit. Each read returns a single byte
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giving the temperature.
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The third interface logs kernel messages on additional alert events.
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Both software and hardware watchdog drivers are available in the standard
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kernel. If you are using the software watchdog, you probably also want
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to use "panic=60" as a boot argument as well.
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The wdt card cannot be safely probed for. Instead you need to pass
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wdt=ioaddr,irq as a boot parameter - eg "wdt=0x240,11".
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The SA1100 watchdog module can be configured with the "sa1100_margin"
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commandline argument which specifies timeout value in seconds.
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The i810 TCO watchdog modules can be configured with the "i810_margin"
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commandline argument which specifies the counter initial value. The counter
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is decremented every 0.6 seconds and default to 50 (30 seconds). Values can
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range between 3 and 63.
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The i810 TCO watchdog driver also implements the WDIOC_GETSTATUS and
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WDIOC_GETBOOTSTATUS ioctl()s. WDIOC_GETSTATUS returns the actual counter value
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and WDIOC_GETBOOTSTATUS returns the value of TCO2 Status Register (see Intel's
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documentation for the 82801AA and 82801AB datasheet).
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Features
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--------
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WDT501P WDT500P Software Berkshire i810 TCO SA1100WD
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Reboot Timer X X X X X X
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External Reboot X X o o o X
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I/O Port Monitor o o o X o o
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Temperature X o o X o o
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Fan Speed X o o o o o
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Power Under X o o o o o
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Power Over X o o o o o
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Overheat X o o o o o
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The external event interfaces on the WDT boards are not currently supported.
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Minor numbers are however allocated for it.
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Example Watchdog Driver
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-----------------------
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#include
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#include
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#include
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int main(int argc, const char *argv[])
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{
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int fd=open("/dev/watchdog",O_WRONLY);
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if(fd==-1)
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{
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perror("watchdog");
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exit(1);
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}
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while(1)
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{
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write(fd,"\0",1);
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fsync(fd);
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sleep(10);
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}
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}
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Contact Information
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People keep asking about the WDT watchdog timer hardware: The phone contacts
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for Industrial Computer Source are:
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Industrial Computer Source
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http://www.indcompsrc.com
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ICS Advent, San Diego
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6260 Sequence Dr.
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San Diego, CA 92121-4371
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Phone (858) 677-0877
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FAX: (858) 677-0895
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>
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ICS Advent Europe, UK
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Oving Road
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Chichester,
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West Sussex,
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PO19 4ET, UK
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Phone: 00.44.1243.533900
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and please mention Linux when enquiring.
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For full information about the PCWD cards see the pcwd-watchdog.txt document.
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