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An MPEG-2 subsystem consisting of the transport demultiplexor, audio decoder, and video decoder is described, along with the supporting processor and memory subsystem. This subsystem is directly applicable to set-top box designs used in a digital television broadcast environment. The advantages of an integrated MPEG-2 subsystem consisting of cores from the IBM Blue Logic library are discussed. The integrated architecture supports a shared memory address space implemented using the PowerPC® local bus (PLB) standard high-speed bus. The resulting memory-management improvements for on-screen display (OSD), decoder rate buffers, audio and video clip data, and transport system data are illustrated. The real-time memory bandwidth and latency requirements for processing an MPEG-2 stream also have an impact on the architecture of the subsystem. Additional enhancements are provided for channel changes, time-base changes, error handling, and enhanced processing in the transport by adding more specialized buses. Programming effort is reduced because the software has less responsibility managing data movement through the system and because the same programming method is used to control all of the MPEG-2 functions.
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