Page 28 - DSP Integrated Circuits

1.6 DSP System Design 13

The vertical partitioning leads to a sequential system. Such systems can be
pipelined so that the subsystems (processors) execute concurrently and pass data
sequentially. The horizontal partitioning leads to a set of subsystems working in
parallel. The subsystems can be autonomous and need not be synchronized since
they do not interchange data. In practice it may not be possible to partition a sys-
tem in a purely vertical or a purely horizontal style. For example, systems with
feedback loops can not be partitioned in this way.

Top-Down Approach
In the top-down design approach, the
whole system is successively parti-
tioned into a hierarchy of subsystems.
On the top level a behavioral descrip-
tion is used. This description is parti-
tioned into a structural description
with behavioral descriptions of the
components. This process of decompo-
sition is then repeated for the compo-
nents until sufficiently simple
components are obtained. The end
result is a functional description of
the system. The subsystems are
assumed to be implemented by the
corresponding hierarchy of virtual
machines. Of course, the design
becomes easier if these hierarchies
are made similar or identical.
Figure 1.13 illustrates the top-down
1
approach using a structural decom-
position. The design process (parti-
tioning) will essentially continue
downward with stepwise refinement of
the subsystem descriptions [13]. It is
advantageous if the partitioning is
done so that the complexities at all Figure 1.13 The top-down approach
hierarchical levels are about the
same.
In the top-down approach we stepwise develop the final system by realizing
and validating each design level in software. By first building the DSP system in
software, the performance can be more accurately estimated. Correctness of the
design as well as of the specification can be verified or validated before making a
commitment to a particular technology and investing in expensive hardware
design. The subsystems are in each design iteration described by using more
and more details so that they become closer and closer to their intended imple-
mentation. An advantage of this approach is that the system is developed from a
global specification and that the successive design models can be checked for

!• The organization of this book essentially follows a top-down style.