The paper addresses the issue of reliability of complex embedded control systems in the safety-critical environment. In this paper, we propose a novel approach to design controller that (i) guarantees the safety of nonlinear physical systems, (ii) enables safe system restart during runtime, and (iii) allows the use of complex, unverified controllers (e.g., neural networks) that drive the physical systems towards complex specifications. We use abstraction-based controller synthesis approach to design a formally verified controller that provides application and system-level fault tolerance along with safety guarantee. Moreover, our approach is implementable using commercial-off-the-shelf (COTS) processing unit. To demonstrate the efficacy of our solution and to verify the safety of the system under various types of faults injected in applications and in the underlying real-time operating system (RTOS), we implemented the proposed controller for the inverted pendulum and three degree-of-freedom (3-DOF) helicopter.
@cite_23: Even after decades of software engineering research, complex computer systems still fail. This paper makes the case for increasing research emphasis on dependability and, specifically, on improving availability by reducing time-to-recover.All software fails at some point, so systems must be able to recover from failures. Recovery itself can fail too, so systems must know how to intelligently retry their recovery. We present here a recursive approach, in which a minimal subset of components is recovered first; if that does not work, progressively larger subsets are recovered. Our domain of interest is Internet services; these systems experience primarily transient or intermittent failures, that can typically be resolved by rebooting. Conceding that failure-free software will continue eluding us for years to come, we undertake a systematic investigation of fine grain component-level restarts, microreboots, as high availability medicine. Building and maintaining an accurate model of large Internet systems is nearly impossible, due to their scale and constantly evolving nature, so we take an application-generic approach, that relies on empirical observations to manage recovery.We apply recursive microreboots to Mercury, a commercial off-the-shelf (COTS)-based satellite ground station that is based on an lnternet service platform. Mercury has been in successful operation for over 3 years. From our experience with Mercury, we draw design guidelines and lessons for the application of recursive microreboots to other software systems. We also present a set of guidelines for building systems amenable to recursive reboots, known as "crash-only software systems."
The notion of restarting as a means of recovery from faults and improving system availability is previously proposed in the literature. These approaches are generally divided into two categories, ) , reactively restart a failed component and ) , prophylactically restart functioning components to prevent state degradation @cite_23 . Our approach, as described in this paper, fits in the former category. However, with slight modification, our design can incorporate periodic self-triggered restarts to prevent future unscheduled unavailable times. In the second form, this work can also be categorized in the latter category.