Evolvable hardware design of combinational logic circuits
Evolvable Hardware (EHW), as an alternative method for logic design, became more attractive recently, because of its algebra-independent techniques for generating selfadaptive self-reconfigurable hardware. This thesis investigates and relates both evaluation and evolutionary processes, emphasizing the need to address problems arising from data complexity. Evaluation processes, capable of evolving cost-optimised fully functional circuits are investigated. The need for an extrinsic EHW approach (software models) independent of the concerns of any implementation technologies is emphasized. It is also shown how the function description may be adapted for use in the EHW approach. A number of issues of evaluation process are addressed: these include choice of optimisation criteria, multi-objective optimisation tedmiques in EHW and probabilistic analysis of evolutionary processes. The concept of self-adaptive extrinsic EHW method is developed. This approach emphasizes the circuit layout evolution together with circuit functionality. A chromosome representation for such system is introduced, and a number of genetic operators and evolutionary algorithms in support of this approach are presented. The genetic operators change the genetic material at the different levels of chromosome representation. Furthermore, a chromosome representation is adapted to the function-level EHW approach. As a result, the modularised systems are evolved using multi-output building blocks. This chromosome representation overcomes the problem of long string chromosome. Together, these techniques facilitate the construction of systems to evolve logic functions of large number of variables. A method for achieving this using bidirectional incremental evolution is documented. It is demonstrated that the integration of a dynamic evaluation process and self-adaptive function-level EHW approach allows the bidirectional incremental evolution to successfully evolve more complex systems than traditionally evolved before. Thereby it provides a firm foundation for the evolution of complex systems. Finally, the universality of these techniques is proved by applying them to multivalued combinational logic design. Empirical study of this application shows that there is no fundamental difference in approach for both binary and multi-valued logic design problems.