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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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All four interfaces provide /dev/watchdog, which when open must be written
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to within a minute or the machine will reboot. Each write delays the reboot
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time another minute. 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 provides /dev/temperature. This is the machine internal temperature in
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degrees farenheit. Each read returns a single byte 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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Features
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--------
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WDT501P WDT500P Software
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Reboot Timer X X X
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External Reboot X X o
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Temperature X o o
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Fan Speed X o o
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Power Under X o o
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Power Over X o o
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Overheat X 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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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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US: 619 677 0877 (sales) 0895 (fax)
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UK: 01243 533900
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France (1) 69.18.74.30
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Industrial Computer Source
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9950 Barnes Canyon Road
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San Diego, CA
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and please mention Linux when enquiring.
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