Edinburgh Napier University

  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.