Advantech RSB-4210 Evaluation Kit User Manual download pdf (Page 95)

87 RSB-4210 User Manual

Chapter 3 Software Functionality

3.11.8.3 The ioctl API

All conforming drivers also support an ioctl API.

Pinging the watchdog using an ioctl:

All drivers that have an ioctl interface support at least one ioctl, KEEPALIVE. This

ioctl does exactly the same thing as a write to the watchdog device, so the main loop

in the above program could be replaced with:

while (1) {

ioctl(fd, WDIOC_KEEPALIVE, 0);

sleep(10);

}

the argument to the ioctl is ignored.

Setting and getting the timeout:

For some drivers it is possible to modify the watchdog timeout on the fly with the

SETTIMEOUT ioctl, those drivers have the WDIOF_SETTIMEOUT flag set in their

option field. The argument is an integer representing the timeout in seconds. The

driver returns the real

timeout used in the same variable, and this timeout might differ from the requested

one due to limitation of the hardware.

int timeout = 45;

ioctl(fd, WDIOC_SETTIMEOUT, &timeout);

printf("The timeout was set to %d seconds\n", timeout);

This example might actually print "The timeout was set to 60 seconds" if the device

has a granularity of minutes for its timeout.

Starting with the Linux 2.4.18 kernel, it is possible to query the current timeout using

the GETTIMEOUT ioctl.

ioctl(fd, WDIOC_GETTIMEOUT, &timeout);

printf("The timeout was is %d seconds\n", timeout);

3.11.8.4 Pretimeouts:

Some watchdog timers can be set to have a trigger go off before the actual time they

will reset the system. This can be done with an NMI, interrupt, or other mechanism.

This allows Linux to record useful information (like panic information and kernel core-

dumps) before it resets.

pretimeout = 10;

ioctl(fd, WDIOC_SETPRETIMEOUT, &pretimeout);

Note that the pretimeout is the number of seconds before the time when the timeout

will go off. It is not the number of seconds until the pretimeout. So, for instance, if

you set the timeout to 60 seconds and the pretimeout to 10 seconds, the pretimout

will go of in 50 seconds. Setting a pretimeout to zero disables it.

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Advantech RSB-4210 Evaluation Kit User Manual Page 95