External Watchdog Microcontrollers, Windowed Watchdogs & Cyclic Plausibility Cross-Checks

Abstract: Preventing software runaway conditions using intelligent, challenge-response windowed watchdog coprocessors.

1. Limitations of Simple Watchdogs A simple watchdog timer cleared by a cyclic timer interrupt can continue to be kicked even if the main application control loop has deadlocked or entered an infinite loop.

2. Question-and-Answer Windowed Watchdogs Safe ECU implements intelligent Q&A watchdogs. The external supervisor microcontroller generates a mathematical challenge. The main CPU must calculate the correct answer using results derived from multiple concurrent threads and respond within a precise time window. If the answer is incorrect or arrives outside the window, the supervisor forces an immediate hardware reset, guaranteeing execution integrity.