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Digital video decoding, enabled by the MPEG-2 video standard, is an important future application for embedded systems, particularly personal digital assistants and other information appliances. Many such systems require portability and wireless communication capabilities, and thus face severe limitations in size and power consumption. This places a premium on integration and efficiency, and favors software solutions for video functionality over specialized hardware. Apart from computation, an equally important problem in video decoding is the data bandwidth and the need to insure adequate data supply. MPEG data sets are very large, and generate significant amounts of excess memory traffic for standard data caches, up to 100 times the amount required for decoding. Yet MPEG data has locality which caches can exploit if properly optimized, providing fast, flexible, and automatic data supply. We propose a set of enhancements which target the specific needs of the heterogeneous types within the MPEG decoder working set. These optimizations significantly improve the efficiency of small caches, reducing cache-memory traffic by almost 70%, and can make an enhanced 4-kB cache perform better than a standard 1 MB cache. This performance improvement can enable high-resolution, full frame rate video playback in cheaper, smaller systems than would otherwise be possible.
Date of Publication: Feb. 2006