Digital systems are highly complex. At their most detailed level, they may consist of
millions of elements, as would be the case if we viewed a system as a collection of
logic gates or pass transistors. From a more abstract viewpoint, these elements may be
grouped into a handful of functional components such as cache memories, floating
point units, signal processors, or real-time controllers. Hardware description lan-guages have evolved to aid in the design of systems with this large number of ele-ments and wide range of electronic and logical abstractions.
The creative process of digital system design begins with a conceptual idea of a log-ical system to be built, a set of constraints that the final implementation must meet,
and a set of primitive components from which to build the system. Design is an itera-tive process of either manually proposing or automatically synthesizing alternative
solutions and then testing them with respect to the given constraints. The design is
typically divided into man y smaller subparts (following the well-known divide-and-conquer engineering approach) and each subpart is further divided, until the whole
design is specified in terms of known primitive components.
The Verilog language provides the digital system designer with a means of describ-ing a digital system at a wide range of levels of abstraction, and, at the same time, pro-vides access to computer-aided design tools to aid in the design process at these levels.
The language supports the early conceptual stages of design with its behavioral con-structs, and the later implementation stages with its structural constructs. During the
design process, behavioral and structural constructs may be mixed as the logical....
