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A comparative study of synchronous and self-timed systolic array architectures

This thesis examines systolic array architectures and their methods of control and communication synchronisation. Systolic array processors suffer from synchronisation problems associated with the clocking mechanism that causally restricts their scalability. To overcome this problem both return-to-zero (RTZ) and non-return-to zero (NRTZ) delay-insensitive self-timed (ST) techniques can be used to realise architectures that operate correctly in the presence of arbitrary delays at all levels in their design. As a consequence, RTZ and NRTZ versions of an existing systolic array architecture, namely the Single instruction Systolic Array (SISA), have been developed in order to investigate the potential for realising architecturally scaleable systolic arrays. The new architectures, called the RTZ and NRTZ ST-SISAs, have been compared with each other and against their synchronous counterpart to establish their relative trade-offs. The new designs exhibit several novel features including: variable length bit-serial data words, average case processing speeds dependent on data word length as well as computational complexity, a novel autonomous inter-processor data communication mechanism and architectural scalability independent of fabrication technology. This thesis introduces an implementation of the RTZ and NRTZ ST-SISA architectures, along with their performance and area characteristics. Guidelines have been developed from the resulting RTZ and NRTZ architectures allowing novel self-timed systolic architectures to be derived.