Synthesising Heterogeneously Encoded Systems

W.B. Toms, D.A. Edwards, A. Bardsley

Abstract

Self-timed datapaths require their data to be encoded in a delay-insensitive manner. The dual-rail encoding is commonly used, but more complex codes offer the possibility of better energy efficiency or fewer wires-per-bit. However, these advantages are often negated by datapath manipulations within large systems that require code-groups to be split and reformed. These overheads may be reduced by heterogeneously encoding circuits based on the datapath requirements within the circuits. In this paper, such an approach is evaluated within the Balsa asynchronous synthesis system. Techniques for synthesising arbitrary m-of-n encodings for datapath components are presented. These implementations allow each channel within a handshake circuit to be assigned an individual encoding. An automated encoding mechanism is described which analyses the datapath requirements of Balsa circuits and assigns codes to channels based on the interaction between sections of datapaths. The performance of the heterogeneous approach is evaluated on two microprocessor implementations.

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