An Aspect-Oriented Approach to Hardware Fault Tolerance for Embedded Systems

Introduction

Current embedded VLSI (Very Large Scale Integration) systems are widespread and operate in multitude of applications in different markets, ranging from life support, industrial control, or avionics to consumer electronics. Benefits of current manufacturing capabilities, in terms of attainable logic density, processing speed and power consumption, become threats to systems dependability, causing higher temperatures, shorter timing budgets and lower noise margins (Narayanan & Xie, 2006). In addition, deep-submicron technologies have both decreased the probability of manufacturing defect-free devices, and increased the likelihood of wear-out related problems and the susceptibility to radiated particles (Constantinescu, 2003). Likewise, communications among devices expose hardware embedded systems to a number of external threats, especially when they are manufactured as an aggregation of off-the-self (OTS) Intellectual Property (IP) cores developed by third, and sometimes untrusted, parties. Nonetheless, reusing these components offers a reduction in time-to-market costs and a rapid integration of technology innovations while minimizing the risk of designs that integrate millions of gates (Rosenstiel, 2004; Vörg, 2003). It is unquestionable that critical systems require different degrees of fault and intrusion tolerance, given the human lives or great investments at stake. However, nowadays, the consideration of resilience in modern VLSI designs, understood as the ability of the system to ensure acceptable levels of dependability and security despite changes, is a requirement even in the industry of non-critical applications, as the occurrence of unexpected failures in consumer products may negatively affect the reputation of manufacturers and undermine the success of new products in the market.

The dependability and security communities widely accept that involving unskilled designers in the development of non-functional strategies (such as fault- and intrusion-tolerance and security) may actually have a negative impact on the global resilience of the deployed solution (Fabre & Pérennou, 1998). There is therefore an emerging requirement for frameworks supporting the separate design of non-functional and system core (functional) mechanisms, and their subsequent integration. In other words, fault and intrusion tolerance mechanisms must be developed by experts, but hardware designers with limited expertise in dependability and security must be able to integrate such mechanisms in their designs to make them resilient to faults and attacks.

How to support such separation of concerns during the design of dependable VLSI solutions remains an open challenge today. Aspect orientation (Kiczales, et al., 1996) provides interesting means to cope with this issue from the first steps of the system design flow, when integrated circuit models become available. The vast majority of modern solutions to digital circuit design revolve around the use of HDL (Hardware Description Language) models. Using such languages, hardware designers program circuits in a modular and hierarchical way. By modifying such models, related circuits can be accordingly adapted and evolved. The notion of metaprogramming, defining programs that automatically reason about and customize the structure of other programs, encompasses this idea. If this customization is specialized for fault tolerance (Taïani, Fabre, & Killijan, 2005), metaprogramming becomes a valuable technique to develop dependable strategies, which can be later (automatically and transparently) deployed onto HDL models following an open compilation process.