Bitstream compression techniques for Virtex 4 FPGAs

This paper examines the opportunity of using compression for accelerating the (re)configuration of FPGA devices, focusing on the choice of compression algorithms, and their hardware implementation cost. As our purpose is the acceleration of the configuration process, estimating the decoder speed also plays a major role in our study. We evaluate a wide range of well-established compression algorithms and we also propose two methods specifically developed for compressing FPGA configuration bitstreams, one based on a static dictionary and the other on arithmetic coding. For the arithmetic coding we propose a statistical model that takes advantage of the particularities of the configuration bitstreams of the Virtex 4 FPGA family. We evaluate the efficiency of the proposed methods along with state of the art compression algorithms on a number of benchmark circuits, some selected from the available open source implementations and some synthetically generated. Our evaluations indicate that using modest resources we can achieve parity and even exceed comercial software in terms of compression ratio, and outperform all other traditional algorithms. All our implemented decompressors are shown to use less than 1.5% of the slices available on the FPGA device.