DP-FPGA: An FPGA architecture optimized for datapaths

This paper presents a new Field-Programmable Gate Array (FPGA) architecture which reduces the density gap between FPGAs and Mask-Programmed Gate Arrays (MPGAs) for datapath oriented circuits. This is primarily achieved by operating on data as a number of identically programmed four-bit slices. The interconnection network incorporates distinct sets of resources for routing control and data signals. These features reduce circuit area by sharing programming bits among four-bit slices, reducing the total number of storage cells required. This paper discusses the requirements of logic blocks and routing structures that can be used to implement typical circuits containing a number of regularly structured datapaths of various sizes, as well as a small number of irregularities. It proposes a specific set of logic block architectures and analyzes it empirically. Experimental results show that the block with the smallest estimated area contains the following features: a lookup table with four read ports, a dedicated carry chain using a bidirectional four-bit carry skip circuit, a four-bit register with enable and direct input capabilities, and four three-state buffers. Further estimates of implementation area predict that the area of a design's datapath can be reduced by a factor of approximately two compared to a conventional FPGA through the use of programming bit sharing.