APB Watchdog Timer

The Watchdog Timer is useful in monitoring the condition where a CPU and software get into an unrecoverable unknown or “stuck” state. Software periodically “kicks” the watchdog by writing to it to reset its timeout counters.

The Watchdog Timer module is a 16-bit down counter with a selectable prescaler, watchdog reset, warning interrupt, and reset controller. Prescale values of 1, 16 and 256 can be selected. The prescaler extends the timer’s range at the expense of precision. Watchdog reset can be used to reset a system after a configurable time lapse without activity. A warning interrupt can be issued a predetermined amount of time before a watchdog reset to indicate a reset is imminent. The reset controller within this module can be used to provide a glitch free version of an external reset to the internal system, and issue an early reset to components before a processor reset.

The Watchdog Timer contains several configuration registers that can be written and read by the processor. Two 4-bit prescalers precede a 16-bit counter. The counter can be clocked at either the input clock rate, or a choice of 2 prescaled rates. The counter can be loaded with a value from a preload register. The watchdog will generate an interrupt when it decrements to the warning time, then a reset when it decrements to zero.