The watchdog in the microcontroller has either a built-in chip or an external chip to realize this function. After the watchdog is started, the software needs to access it continuously according to the setting time. That is to say, if you have a dog, you have to take care of it, feed it regularly, and once you leave it alone over the time to eat, it barks. When it is called, it generates a reset signal, or generates a specific interrupt signal. If the software can access it regularly, it will not shout, and if the program runs or crashes, it will generate a reset signal that will wake up the MPU again.