CME136686LX Hardware Manual - RTD Embedded Technologies ...

Watchdog Timer Control
The cpuModule includes a Watchdog Timer, which provides protection against programs “hanging”, or getting
stuck in an execution loop where they cannot respond correctly. The watchdog timer consists of a counter, a
reset generator, and an interrupt generator. When the counter reaches the interrupt time-out, it can generate
an interrupt. When the counter reaches the reset time-out, the system is reset. The counter is “refreshed,” or set
back to zero by reading from a specific register. The watchdog can also be put into an “inactive” state, in which
no resets or interrupts are generated.
The ability to generate an interrupt allows the application to gracefully recover from a bad state. For example,
consider a system that has a reset time-out of 2 seconds, interrupt time-out of 1 second, and the watchdog timer
is refreshed every 0.5 seconds. If something goes wrong, an interrupt is generated. The Interrupt service routine
then attempts to restart the application software. If it is successful, the application is restarted in much less time
than a full reboot would require. If it is not successful, the system is rebooted.
Due to system latency, it is recommended that the Watchdog be refreshed at about half of the reset time-out
period, or half of the interrupt time-out period, whichever is applicable.
BDM-610000065 Rev C Chapter 4: Using the cpuModule 77