A watchdog timer is a hardware countdown timer that automatically resets the MCU if the firmware fails to periodically reload ("kick") it before it expires. It solves the problem that embedded devices run unattended and firmware can hang, an infinite loop, a deadlock, a corrupted state machine, a peripheral call that never returns, with no human present to press reset. Healthy code kicks the watchdog regularly, keeping the counter from reaching zero; if the code hangs and stops kicking, the counter expires and the hardware forces a reset, rebooting the device into a known-good state. So it's a liveness mechanism and a last line of recovery: it doesn't fix the bug, but it ensures a wedged device recovers automatically instead of staying dead until someone power-cycles it. It's essentially mandatory in any unattended or safety-relevant product.
Embedded Systems Fundamentals · Interview question
What is a watchdog timer and what problem does it solve?
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The Watchdog Timer
The hardware that resets a hung MCU: a countdown timer firmware must periodically kick, why you kick only from healthy code, and the window-watchdog twist.
More The Watchdog Timer questions
Where in your code should you kick the watchdog, and what's the common mistake?What's the difference between an independent watchdog and a window watchdog?How do you choose the watchdog timeout, and what goes wrong at the extremes?Why does your chip keep resetting when you pause at a breakpoint, and how do you handle long legitimate operations?
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