This chapter looks at the way in which VHDL is used in digital systems design, the historical reasons why VHDL was created and the international project to maintain and upgrade the language.
1.1 The VHDL Design Cycle
From its conception, VHDL was intended to support all levels of the hardware design cycle. This is clear from the preface of the Language Reference Manual (LRM) (IEEE-1076, 2008) which defines the language, from which the following quote has been taken:
VHDL is a formal notation intended for use in all phases of the creation of electronic systems. Because it is both machine readable and human readable, it supports the development, verification, synthesis, and testing of hardware designs; the communication of hardware design data; and the maintenance, modification, and procurement of hardware.
The key phrase is ‘all phases’. This means that VHDL is intended to cover every level of the design cycle from system specification to netlist. As a result, the language is rather large and cumbersome. However, this does not necessarily make it difficult to learn. It is best to think of VHDL as a hybrid language, containing features appropriate to one or more of the stages of the design cycle, so that each stage is in effect covered by a separate language that also happens to be a subset of the whole. Each subset is relatively easy to learn, provided there is guidance as to what is in, and what is not in, that subset.
In the idealised design process, there ...