Functional Design using Behavioural and Structural Components

In previous work we have demonstrated how the functional language SAFL can be used as a behavioural hardware description language. Other work (such as µFP and Lava) has demonstrated that functional languages are apposite for structural hardware description. One of the strengths of systems such as VHDL and Verilog is their ability to mix structuraland behavioural-level primitives in a single specification. Motivated by this observation, we describe a unified framework in which a stratified functional language is used to specify hardware across different levels of abstraction: Lava-style structural expansion is used to generate acyclic combinatorial circuits; these combinatorial fragments are composed at the SAFL level. We demonstrate the utility of this programming paradigm by means of a realistic case-study. Our tools have been used to specify, simulate and synthesise a DES encryption/decryption circuit. Area-time performance figures are presented.