A Fully Pipelined and Dynamically Composable Architecture of CGRA

Future processor chips will not be limited by the transistor resources, but will be mainly constrained by energy efficiency. Reconfigurable fabrics bring higher energy efficiency than CPUs via customized hardware that adapts to user applications. Among different reconfigurable fabrics, coarse-grained reconfigurable arrays (CGRAs) can be even more efficient than fine-grained FPGAs when bit-level customization is not necessary in target applications. CGRAs were originally developed in the era when transistor resources were more critical than energy efficiency. Previous work shares hardware among different operations via modulo scheduling and time multiplexing of processing elements. In this work, we focus on an emerging scenario where transistor resources are rich. We develop a novel CGRA architecture that enables full pipelining and dynamic composition to improve energy efficiency by taking full advantage of abundant transistors. Several new design challenges are solved. We implement a prototype of the proposed architecture in a commodity FPGA chip for verification. Experiments show that our architecture can fully exploit the energy benefits of customization for user applications in the scenario of rich transistor resources.