The CircuitPython watchdog module implements a watchdog timer that can be used to detect and recover from locked or stalled processes running on the microcontroller.

The watchdog is configured for a specified timeout period and is activated. Then, the code must feed the dog at least once within every timeout interval. Letting the timeout elapse without feeding the dog will cause it to bite. When the watchdog bites, it will typically reset the device back into a clean state.

Watchdog timers are used frequently in embedded systems and robotics. Especially when hardware is deployed in remote places that are not quickly or easily accessible for a human to intervene in the event of malfunctions. Consumer electronics often use them to ensure that the gadget won't freeze or lock up. 

Parts

Generally, most devices from the Rasperry Pi, Nordic, and Espressif ports can use the watchdog library, as can SAMD51 devices, but not SAMD21. Individual boards may have the module disabled in order to account for limited flash space. Click "Available on these boards" on the watchdog docs page for a comprehensive list of supported boards.

The Feathers listed below all support watchdog, so do most Metros, other form factors, and variations based on the same chips. Consult the board support list linked above to confirm support for specific hardware.