A design flow based on modular refinement

We propose a practical methodology based on modular refinement to design complex systems. The methodology relies on modules with latency-insensitive interfaces so that the refinements can change the timing contract of a module without affecting the overall functional correctness of the system. Such refinements can exacerbate the unit testing problem for modules whose specifications admit a set of output behaviors for the same input (non-determinism), or modules whose input behavior may be affected by past outputs (feedback). We avoid the difficult problem of generating appropriate unit tests for such modules by using system-level tests as unit tests to verify the correctness of refined modules. We illustrate our methodology by showing how one might develop a microprocessor with an in-order pipeline. We then develop a superscalar pipeline using the in-order pipeline as the starting point. Our methodology leverages the effort of design exploration to reduce the effort of specifying interface contracts and unit testing.