9 - Digital signal processors

Abstract

This chapter focuses on hardware issues associated with digital signal processor chips, and compares the characteristics of a digital signal processing (DSP) to a conventional, general-purpose microprocessor. This chapter further discusses software issues and some common algorithms. There are mainly four different ways of implementing the required hardware in digital signal processing application: conventional microprocessor, DSP chip, bitslice or wordslice approach, and dedicated hardware, field programmable gate array (FPGA), application specific integrated circuit (ASIC). If higher processing capacity is required, it is common to connect a number of processors, working in parallel in a larger system. This can be done in different ways, either in a single instruction multiple data (SIMD) or in a multiple instruction multiple data (MIMD) structure. In an SIMD structure, all the processors are executing the same instruction but on different data streams. Such systems are sometimes also called vector processors. In an MIMD system, the processors may be executing different instructions. Most of the common processors today are of the complex instruction set computer (CISC) type. Further, these instructions often require more than 1 machine cycle to execute. In many cases, reduced instruction set computers (RlSC)-type processors may perform better in signal processing applications. In an RISC processor, no instruction occupies more than one memory word; it can be fetched in 1 bus cycle and executes in 1 machine cycle. On the other hand, many RISC instructions may be needed to perform the same function as one CISC-type instruction, but in the RISC case, one can get the required complexity only when needed.