As predicted by Gordon Moore, the number of transistors on a chip has roughly doubled every two years. Microprocessors featuring over a billion transistors are no longer science fiction. For example, Intel's Itanium 9000 series and Intel's Xeon 7400 series of processors feature 1.7 and 1.9 billion transistors respectively. To keep up with the emerging needs of contemporary very large scale integration (VLSI) design, industrial hardware description languages (HDLs) like Verilog and VHDL must be significantly enhanced. This thesis pinpoints some of the main shortcomings of the latest Verilog standard (IEEE 1364-2005) and shows how to overcome them by extending the language in a backward compatible way.
To be able to cope with more complex circuits, well-understood higher-level abstraction mechanisms are needed. Verilog is already equipped with promising generative constructs making it possible to concisely describe a family of circuits as a parameterized module; however these constructs suffer from two problems: First, their expressivity is limited and second, they are not adequately supported by current tools. For instance, there are no static guarantees about the properties of the description generated as a result of instantiating a generic description with particular parameter values.
Addressing both problems while remaining backward compatible led us to select a statically typed two-level languages (STTL) formal framework. By formalizing a core subset of Verilog as an STTL, we were able to define a static type system capable of: (1) checking the realizability of a description, (2) detecting bus width mismatches and array bounds violations, and (3) providing parametric guarantees on the resources required to realize a generic description. The power of the chosen framework is once more demonstrated as it also allows us to enrich the language with a new set of constructs that are designed to be expanded away when instantiated.
To experiment with these ideas we implemented VPP, a Verilog Preprocessor with a built-in type checker. VPP is an unobtrusive tool accepting extended Verilog descriptions but generating descriptions compatible with any tool compliant with the Verilog standard.
Our experience throughout this research showed that STTLs present a particularly suitable framework to formalize and implement generative features of a language.