Watchdog Timer

CORE DEFINITION

A watchdog timer is a computer hardware timing device that, when the system's main program encounters certain error events, such as a hang or failure to periodically clear the timer's internal count (usually by sending a clear signal to the timer), sends a reset, restart, or shutdown signal to the system, restoring it from a suspended state to normal operation. Once activated, the watchdog cannot be stopped. Typically, the counter continues counting even when the system is in sleep mode, but on some chips, the watchdog in low-power mode only retains register data without counting. The operation of a watchdog timer can be more complex: it may attempt to store debug information to persistent media (usually non-volatile memory), for example, to store information about the cause of a fault for later analysis and troubleshooting. In such usage, another simpler watchdog timer is needed to ensure that the original watchdog timer completes the information storage within a precise time; if not, the simpler watchdog timer sends a reset, restart, or shutdown signal to the system.