Design and Architectural Exploration of Expression-Grained Reconfigurable Arrays

Reconfigurable Arrays combine the benefit of spatial execution, typical of hardware solutions, with that of programmability, present in microprocessors. When mapping software applications (or parts of them) onto hardware, however, FPGAs often provide more flexibility than is needed, and do not implement coarser-level operations efficiently. Therefore, Coarse Grained Reconfigurable Arrays (CGRAs) have been proposed to this aim. While most CGRA designs feature an array cell of the order of an ALU, this paper proposes a new kind of coarse grained array, called EGRA (Expression-Grained Reconfigurable Array), featuring a cell composed of a cluster of ALUs with flexible interconnect. The EGRA attempts to further close the performance gap between reconfigurable and hardwired logic by implementing an arithmetic/logic expression per cell, rather than a single operation. A mapping methodology is proposed that can retargetably compile to a family of EGRAs, therefore enabling architectural exploration of the granularity of the proposed cell. Performance results on a number of embedded applications show that EGRAs can be used as a reconfigurable fabric for customizable processors, outperforming more traditional CGRA designs.