Watchdog timer

Firmware is expected to "kick" the watchdog regularly. If a bug, lockup or electrical glitch stops that from happening, the timer expires and resets the chip. For a device installed in a wall, on a roof or inside a machine, this is often the difference between a brief hiccup and a service visit.

Done badly, a watchdog hides problems: firmware that kicks it from a simple timer interrupt will keep a half-dead system alive. Better practice is to kick it only after confirming that every critical task is making progress, to record the cause of each reset, and to report reset counts in telemetry so field problems become visible. Independent or windowed watchdogs add protection where safety matters.