Self-Stabilizing Micro Controller for Large-Scale Sensor Networks in Spite of Program Counter Corruptions Due to Soft Errors

For large installations of networked embedded systems it is important that each entity is self-stabilizing, because usually there is nobody to restart nodes that have hung up. Self-stabilization means to recover from temporary failures (soft errors) and adapt to a change of network topology caused by permanent failures. On the software side self-stabilizing algorithms must assume that the hardware is executing the software correctly. In this paper we discuss cases in which soft errors invalidate this assumption, especially in cases where CPU registers or the watchdog timer are affected by the fault. Based on the observation that a guaranteed self-stabilization is only possible as long as the watchdog-timer is working properly after temporary failures, we propose and compare three different approaches that meet the requirements of sensor networks, to solve this problem with a combination of hardware- and software-modifications: 1) A run-time verification of every watchdog access 2) A completely hardware-based approach, without any software modifications 3) A ²X byte code alignment, to realign a corrupted program counter Furthermore we determine the average code-size increase and evaluate necessary hardware-modifications that come along with each approach.