Page 293 - DSP Integrated Circuits

278 Chapter 7 DSP System Design

In this chapter, we will first discuss a highly structured design approach
based on a direct mapping technique. We stress that the scheduling, resource allo-
cation, and assignment steps are crucial to a successful design. We will discuss dif-
ferent formulations of the scheduling problem as well as some common
optimization techniques. We will also demonstrate the shortcomings of conven-
tional scheduling techniques and present a formulation of the scheduling problem
that facilitates optimal scheduling.

7.2 A DIRECT MAPPING TECHNIQUE

Generally, an algorithm can be mapped to a software-hardware architecture
either by direct mapping or by first mapping the algorithm to an intermediate, vir-
tual machine followed by mapping to a programmable hardware structure. The
first approach typically aims at high-performance, fixed-function systems whereas
the second method sacrifices performance in an attempt to reduce both the design
effort and cost by using standard digital signal processors.
Next, we outline the direct mapping tech-
nique that is suitable for design of fixed-function
systems. The main steps in the direct mapping
technique are shown in Figure 7.2. We will follow
this approach in the case studies.

1. Ideally, the specification of the system
contain a complete specification of the
system and its components. In reality,
however, the specifications of the
components from which the system is
built must be derived from the system
specification. In a top-down design
approach component specification at a
given system level will depend on the
results of the synthesis done at the
higher levels. Hence, the component
specifications will evolve as the design
progresses.
2. A good DSP algorithm is selected and
tuned to the application. Usually, a high-
level language is used to develop and
validate the correctness of the DSP
algorithm. Note that a software
implementation of the DSP algorithm
can serve as specification for the next
design phase.
3. In the next phase, the algorithm is
successively partitioned into a hierarchy
Figure 7.2 The main steps ir
of processes. We refer to the tasks in the the DSP system
algorithm as processes, for example, design phase—
storage of data is considered as a idealistic view