Selective flexibility: breaking the rigidity of datapath merging

Hardware specialization is often the key to efficiency for programmable embedded systems, but comes at the expense of flexibility. This paper combines flexibility and efficiency in the design and synthesis of domain-specific datapaths. We merge all individual paths from the Data Flow Graphs (DFGs) of the target applications, leading to a minimal set of required resources; this set is organized into a column of physical operators and cloned, thus generating a domain-specific rectangular lattice. A bus-based FPGA-style interconnection network is then generated and dimensioned to meet the needs of the applications. Our results demonstrate that the lattice has good flexibility: DFGs that were not used as part of the datapath creation phase can be mapped onto it with high probability. Compared to an ASIC design of a single DFG, the speed of our domain-specific coarse-grained reconfigurable datapath is degraded by a factor up to 2×, compared to 3--4× for an FPGA; similarly, our lattice is up to 10× larger than an ASIC, compared to 20--40× for an FPGA. We estimate that our array is up to 6× larger than an ASIC accelerator, which is synthesized using datapath merging and has limited or null generality.