SKETCHILOG: Sketching combinational circuits

Despite the progress of higher-level languages and tools, Register Transfer Level (RTL) is still by far the dominant input format for high performance digital designs. Experienced designers can directly express their microarchitectural intuitions in RTL. Yet, RTL is terribly verbose, burdened with trivial details, and thus error prone. In this paper, we augment a modern RTL language (Chisel) with new semantic elements to express an imprecise specification: a sketch. We show how, in combination with a naïve, unoptimized, but functionally correct reference, a designer can utilize the language and supporting infrastructure to focus on the key design intuition and omit some of the necessary details. The resulting design is exactly or almost exactly as good as the one the designer could have achieved by spending the time to manually complete the sketch. We show that, even limiting ourselves to combinational circuits, realistic instances of meaningful design problems are solved quickly, saving considerable design and debugging effort.