A fast asynchronous Huffman decoder for compressed-code embedded processors

Abstract

This paper presents the architecture and design of a high-performance asynchronous Huffman decoder for compressed-code embedded processors. In such processors, embedded programs are stored in compressed form in instruction ROM then are decompressed on demand during instruction cache refill. The Huffman decoder is used as a code decompression engine. The circuit is non-pipelined, and is implemented as an iterative self-timed ring. It achieves a high-speed decode rate with very low area overhead. Simulations using Lsim show an average throughput of 32 bits/25 ns on the output side (or 163 MBytes/sec, or 1303 Mbit/sec), corresponding to about 889 Mbit/sec on the input side. The area of the design is extremely small: under 1 mm/sup 2/ in a 0.8 micron full-custom layout. The decoder is estimated to have higher throughput than any comparable synchronous Huffman decoder (after normalizing for feature size and voltage), yet is much smaller than synchronous designs. Its performance is also 83% faster than a recently published asynchronous Huffman decoder using the same technology.