The Verilog Hardware Description Language, Fifth Edition

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....