Timeless Truths about Sequential Circuits

We suggest the use of a declarative programming language to design and describe circuits, concentrating on the use of higher-order functions to structure and simplify designs. In order to describe sequential circuits, we use a language , fp, which abstracts from temporal iteration. The practicalities of vlsi design make regularity attractive, and we describe the use of familiar higher order functions to capture spatial iteration. By reasoning about circuits rather than signals (programs rather than data) one abstracts from the sequential nature of a circuit. By reasoning about forms of circuit (higher order functions) one can devise implementation strategies for whole classes of algorithms. Reasoning about fp is formally quite similar to reasoning about fp. In this paper we identify the semantic content of the formal similarity between fp and fp. This makes it possible to carry over from conventional functional programming those intuitions we have about algorithm design. It also makes it possible to conduct parts of a design in the simpler world of static calculations, with conndence in the correctness of the corresponding sequential circuit. Concurrent systems We begin from the premiss that designing a logic circuit is essentially the same activity as writing a program, but that the constraints on the programmer are in this case rather unusual. The eecient use of vlsi resources requires the designer to write a highly concurrent program, consisting of a very large number of simple but simultaneously operating processes which cooperate to achieve the desired eeect. Economic considerations dictate that many of these processes have to be identical,