Static versus scheduled interconnect in Coarse-Grained Reconfigurable Arrays

Spatially-tiled architectures, such as coarse-grained reconfigurable arrays (CGRAs), are powerful architectures for accelerating applications in the digital-signal processing, embedded, and scientific computing domains. In contrast to field-programmable gate arrays (FPGAs), another common accelerator, they typically time-multiplex their processing elements and are word rather than bit-oriented. These differences lead us to re-examine some of the traditional architecture choices made for FPGAs as we move to these coarser-granularity architectures. In this paper we study the efficiency of time-multiplexing global interconnect as architectures scale from single-bit to multi-bit datapaths. Using the Mosaic infrastructure, we analyzed the design trade-offs involved in static vs. time-multiplexed routing for global interconnect channels, as well as the benefit of including a dedicated bit-wide control interconnect to supplement the word-wide datapath of a CGRA. We show that a time-multiplexed interconnect is beneficial in these coarse-grained systems, reducing the area-energy product to 0.32times the area-energy product of a fully static interconnect. We also show that for our benchmarks, which include single-bit control logic, providing both word and bit-wide interconnect resources further reduces the area-energy product to 0.94times that of an exclusively word-wide interconnect.