Constructing hardware-software systems reliably from a single description

The study of computing is split at an early stage between the branches that deal with hardware and software; there is also a corresponding split in professional specialisation. This paper explores the essential unity of the two branches and attempts to find a common framework within which hardware-software codesigns can be formulated, transformed and reasoned about. We use the notion of program transformation to map a user´s program into a variety of forms. These forms can then be interpreted as hardware, as software, or as machine code for an application-specific processor together with a hardware description of the processor. This paper deals with implementations which use at least two different forms simultaneously. A single application program can exploit the inherent, and widely differing, cost-performance characteristics that each of these forms has, in order to give hardware support to the parts of the application that need it most. We typically use field-programmable gate arrays in conjunction with microprocessors to implement our systems. This enables us to construct realistic working hardware-software systems in hours or even minutes