Evolvable hardware (EHW) has attracted increasing attention since early 1990's with the advent of easily reconfigurable hardware such as field programmable gate arrays (FPGAs). It promises to provide an entirely new approach to complex electronic circuit design and new adaptive hardware. EHW has been demonstrated to be able to perform a wide range of tasks from pattern recognition to adaptive control. However, there are still many fundamental issues in EHW which remain open. This paper reviews the current status of EHW, discusses the promises and possible advantages of EHW, and indicates the challenges we must meet in order to develop practical and large-scale EHW. 1 Introduction Evolvable hardware (EHW) refers to hardware that can change its architecture and behaviour dynamically and autonomously by interacting with its environment. At present, almost all EHW uses an evolutionary algorithm (EA) as their main adaptive mechanism. One of the key motivations behind EHW is to learn from N...

The growth and operation of all living beings are directed by the interpretation, in each of their cells, of a chemical program, the DNA string or genome. This process is the source of inspiration for the Embryonics (embryonic electronics) project, whose final objective is the design of highly robust integrated circuits, endowed with properties usually associated with the living world: self-repair (cicatrization) and self-replication. The Embryonics architecture is based on four hierarchical levels of organization. 1) The basic primitive of our system is the molecule, a multiplexer-based element of a novel programmable circuit. 2) A finite set of molecules makes up a cell, essentially a small processor with an associated memory. 3) A finite set of cells makes up an organism, an application-specific multiprocessor system. 4) The organism can itself replicate, giving rise to a population of identical organisms. We begin by describing in detail the implementation of an artificial cell characterized by

Biological organisms are among the most robust systems known to man. Their robustness is based on a set of processes which cannot be adapted directly to the world of silicon, but can provide an inspiration for the design of robust circuits. This paper introduces a multiplexerbased FPGA which we made capable of self-test and self-repair using an approach loosely based on biological mechanisms at the cellular level. The system is designed to provide on-line self-test and selfrepair using a completely distributed system and a minimal amount of additional logic. 1.

Self-reproducing, cellular automata-based systems developed to date broadly fall under two categories; the first consists of machines which are capable of performing elaborate tasks, yet are too complex to simulate, while the second consists of extremely simple machines which can be entirely implemented, yet lack any additional functionality aside from self-reproduction. In this paper we present a self-reproducing system which is completely realizable, while capable of executing any desired program, thereby exhibiting universal computation. Our starting point is a simple self-reproducing loop structure onto which we "attach" an executable program (Turing machine) along with its data. The three parts of our system (loop, program, data) are all reproduced, after which the program is run on the given data. The system reported in this paper has been simulated in its entirety; thus, we attain a viable, self-reproducing machine with programmable capabilities. 1 Introduction The study of art...

Artificial evolution can integrate fault tolerance considerations into the automatic design process, producing inherently fault-tolerant designs without explicit redundant parts. Population dynamics can give rise to some level of fault tolerance `for free.' Requirements for fault tolerance can also be incorporated into the fitness function. The practicalities of these methods are investigated, grounded in the study of a real-world evolved electronic control system for a robot.

Biological organisms are among the most intricate structures known to man, exhibiting highly complex behavior through the massively parallel cooperation of numerous relatively simple elements, the cells. As the development of computing systems approaches levels of complexity such that their synthesis begins to push the limits of human intelligence, engineers are starting to seek inspiration in nature for the design of computing systems, both at the software and at the hardware levels. This paper will present one such endeavor, notably an attempt to draw inspiration from biology in the design of a novel digital circuit: a field-programmable gate array (FPGA). This reconfigurable logic circuit will be endowed with two features motivated and guided by the behavior of biological systems: self-replication and self-repair. 1

A novel approach to hardware fault tolerance is demonstrated that takes inspiration from the human immune system as a method of fault detection. The human immune system is a remarkable system of interacting cells and organs that protect the body from invasion and maintains reliable operation even in the presence of invading bacteria or viruses. This paper seeks to address the field of electronic hardware fault tolerance from an immunological perspective with the aim of showing how novel methods based upon the operation of the immune system can both complement and create new approaches to the development of fault detection mechanisms for reliable hardware systems. In particular, it is shown that by use of partial matching, as prevalent in biological systems, high fault coverage can be achieved with the added advantage of reducing memory requirements. The development of a generic finite-state-machine immunization procedure is discussed that allows any system that can be represented in such a manner to be “immunized” against the occurrence of faulty operation. This is demonstrated by the creation of an immunized decade counter that can detect the presence of faults in real time.

Since the advent of computers numerous approaches have been taken to create hardware systems that provide a high degree of reliability even in the presence of errors. This paper seeks to address the problem from a biological perspective using the human immune system as a source of inspiration. The immune system uses many ingenious methods to provide reliable operation in the body and so may suggest how similar methods can be used in the future design of reliable systems. The paper addresses this challenge through the implementation of an immunised finite state machine based counter. The proposed methods demonstrate how through a process of self/non-self differentiation the hardware immune system will create a set of tolerance conditions to monitor the change in states of the hardware. Potential faults may then be flagged, assessed and the appropriate recovery action taken.

of the work presented in this thesis has been previously published as listed below. Although some of these papers have co-authors, the work appearing in this thesis is entirely my own, with the exception of parts of chapter 3, which presents work jointly carried out by myself and Adrian Thompson. The respective contributions to this work will be explicitly stated at the beginning of the chapter. List of Previous Publications Kuntz, P., Layzell, P., & Snyers, D. (1997). A Colony of Ant-like Agents for Partitioning

Special-purpose parallel systems, and in particular cellular SIMD (Single-Instruction Multiple-Data-Stream) and SPMD (Single-Program Multiple-Data-Stream) array processors are very interesting approaches for handling many computationally-intensive applications. These systems consist of an array of identical processing elements executing the same operations (at the instruction or at the program level, respectively) on different sets of data. The main obstacles to the widespread use of application-speciÞc arrays of processors are, of course, development time and price: the time required for the design of such systems is usually measured in months, if not years, while the cost of custom VLSI circuits makes such designs too expensive for most situations. A major goal of the Embryonics project, the research project which provides the framework for this thesis, is the development of such an array of processors, or cells, inspired by biological cellular processes, and in particular by the embryological processes of living beings. These processors, relatively simple binary decision