3.2 Hardware Design

Hardware design, of course, is more constrained than software by the physical world. It is instructive to examine the abstractions that have worked for hardware, such as synchronous design. The synchronous abstraction is widely used in hardware to build large, complex, and modular designs, and has recently been applied to software [6], particularly for designing embedded software.
Hardware models are conventionally constructed using hardware description languages such as Verilog and VHDL; these languages realize a discrete-event model of computation that makes time a first-class concept, information shared by all components. Synchronous design is done through a stylized use of these languages. Discrete-event models are often used for modeling complex systems. particularly in the context of networking, but have not yet (to my knowledge) been deployed into embedded system design.
Conceptually, the distinction between hardware and software, from the perspective of computation, has only to do with the degree of concurrency and the role of time. An application with a large amount of concurrency and a heavy temporal content might as well be thought of using hardware abstractions, regardless of how it is implemented. An application that is sequential and has no temporal behavior might as well be thought of using software abstractions, regardless of how it is implemented. The key problem becomes one of identifying the appropriate abstractions for representing t
he design.