Shared buffer implementations of signal processing systems using lifetime analysis techniques

There has been a proliferation of block-diagram environments for specifying and prototyping digital signal processing (DSP) systems. These include tools from academia such as Ptolemy and commercial tools such as DSPCanvas from Angeles Design Systems, signal processing work system (SPW) from Cadence, and COSSAP from Synopsys. The block diagram languages used in these environments are usually based on dataflow semantics because various subsets of dataflow have proven to be good matches for expressing and modeling signal processing systems. In particular, synchronous dataflow (SDF) has been found to be a particularly good match for expressing multirate signal processing systems. One of the key problems that arises during synthesis from an SDF specification is scheduling. Past work on scheduling from SDF has focused on optimization of program memory and buffer memory under a model that did not exploit sharing opportunities. In this paper, we build on our previously developed analysis and optimization framework for looped schedules to formally tackle the problem of generating optimally compact schedules for SDF graphs. We develop techniques for computing these optimally compact schedules in a manner that also attempts to minimize buffering memory under the assumption that buffers will be shared. This results in schedules whose data memory usage is drastically lower than methods in the past have achieved. The method we use is that of lifetime analysis; we develop a model for buffer lifetimes in SDF graphs and develop scheduling algorithms that attempt to generate schedules that minimize the maximum number of live tokens under the particular buffer lifetime model. We develop several efficient algorithms for extracting the relevant lifetimes from the SDF schedule. We then use the well-known first-fit heuristic for packing arrays efficiently into memory. We report extensive experimental results on applying these techniques to several practical SDF systems and show improvements that average 50% over previous techniques, with some systems exhibiting up to an 83% improvement over previous techniques.