Permuting streaming data using RAMs

This article presents a method for constructing hardware structures that perform a fixed permutation on streaming data. The method applies to permutations that can be represented as linear mappings on the bit-level representation of the data locations. This subclass includes many important permutations such as stride permutations (corner turn, perfect shuffle, etc.), the bit reversal, the Hadamard reordering, and the Gray code reordering. The datapath for performing the streaming permutation consists of several independent banks of memory and two interconnection networks. These structures are built for a given streaming width (i.e., number of inputs and outputs per cycle) and operate at full throughput for this streaming width. We provide an algorithm that completely specifies the datapath and control logic given the desired permutation and streaming width. Further, we provide lower bounds on the achievable cost of a solution and show that for an important subclass of permutations our solution is optimal. We apply our algorithm to derive datapaths for several important permutations, including a detailed example that carefully illustrates each aspect of the design process. Lastly, we compare our permutation structures to those of Järvinen et al. 2004, which are specialized for stride permutations.