The window watchdog mode supports several applications that can be supported simultaneously.
Reset the Timer Too Soon
When the system software enters the interrupt handler to restart the watchdog timer, it is possible that the software erroneously stays in the interrupt routine and repeatedly issues the timer restart command in relatively quick succession. This can be detected by the SWDT and cause it to generate an interrupt. The window mode detects the high rate of software writes to the timer to prevent the software from being stuck in a watchdog interrupt routine.
Bound the Performance
An additional use of the watchdog timer is to ensure the performance of the system stays within expected bounds. A narrow window of time is given to the open window that is carefully calculated to be achievable under all correct operating scenarios. If a fault occurs that causes some performance degradation, the timer is not reset within the narrow available time window and the watchdog timer issues an interrupt. If the watchdog timer detects a problem, it generates a system reset request event.
The window watchdog timer can be programmed to always be on as the health of the system is monitored and evaluated. The always-on operation uses the fail count as a measure of how well the watchdog timer is being serviced.