Safety system challenge-and-response using modified watchdog timer

Abstract

Some embodiments of the present disclosure relate to a watchdog timer having an enhanced functionality that enables the watchdog timer to monitor a process flow of the microprocessor on a task-by-task basis that enables a simple output signal to be used to determine if the watchdog timer is malfunctioning. The watchdog timer has a state machine that increments a state variable from an initial value over a watchdog period. A deterministic service request, received from a microprocessor, controls operation of the watchdog timer. The deterministic service request has an indicator of a monitoring operation to be performed, a password, and an estimated state variable. A comparison element determines if the microprocessor is operating properly based upon a comparison of the received password to an expected password and the received estimated state variable to an actual state variable.