Evolvable hardware (EHW) uses simulated evolution to generate an electronic circuit with specific characteristics, and is generally implemented on Field Programmable Gate Arrays (FPGAs). EHW has proven to be successful at producing small novel circuits for applications such as robot control and image processing, however, traditional approaches, in which the FPGA configuration is directly encoded on the chromosome, have not scaled well with increases in problem and FPGA architecture complexity. One of the methods proposed to overcome this is the incorporation of a growth process, known as morphogenesis, into the evolutionary process. However, existing approaches have tended to abstract away the underlying architectural details, either to present a simpler virtual FPGA architecture, or a biochemical model that hides the relationship between the cellular state and the underlying hardware. By abstracting away the underlying architectural details, EHW has moved away from one of its key strengths, that being to allow evolution to discover novel solutions free of designer bias. Also, by separating the biological model from the target FPGA architecture, too many assumptions and arbitrary decisions need to be made, which are liable to lead to the growth process failing to produce the desired results. In this thesis a new approach to applying morphogenesis to gate-level FPGA- based EHW is presented, whereby circuit growth is closely tied to the underlying gate-level architecture, with circuit growth being driven largely by the state of gate-level resources of the FPGA. An investigation into the applicability of biological processes, structures and mechanisms to morphogenetic EHW (MGEHW) is conducted, and the resulting design elaborated. The developed MGEHW system is applied to solving a signal routing problem with irregular and severe constraints on routing resources. It is shown that the morphogenetic approach outperforms a traditional EHW approach using a direct encoding, and importantly, is able to scale to larger, more complex, signal routing problems without any significant increase in the number of generations required to find an optimal solution. With the success of the MGEHW system in solving primarily structural prob- lems, it is then applied to solving a combinatorial function problem, specifically a one-bit full adder, with a more complete set of FPGA resources. The results of these experiments, together with the previous experiments, has provided valuable information that when analysed has enabled the identification of the critical factors that determine the likelihood of an EHW problem being solvable. In particular this has highlighted the importance of effective fitness feedback for guiding evolution towards its desired goal. Results indicate that the gate-level morphogenetic approach is promising. The research presented here is far from complete; many avenues for future research have opened. The MGEHW system that has been developed allows further research in this area to be explored experimentally. Some of the most fruitful directions for future research are described.
| Identifer | oai:union.ndltd.org:ADTP/265223 |
| Date | January 2006 |
| Creators | Lee, Justin Alexander |
| Publisher | Queensland University of Technology |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
| Rights | Copyright Justin Alexander Lee |
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