Revisiting and-inverter cones.

ABSTRACTAnd-Invert Cones (AICs) have been suggested as an alternative to the ubiquitous Look-Up Tables (LUTs) used in commercial FPGAs. The original article suggesting the new architecture made some untested assumptions on the circuitry needed to implement AIC architectures and did not develop completely the toolset necessary to assess comprehensively the idea. In this paper, we pick up the architecture that some of us proposed in the original AIC paper and try to implement it as thoroughly as we can afford. We build all components for the logic cluster at transistor level in a 40~nm technology as well as a LUT-based architecture inspired by Altera's Stratix~IV. We first determine that the characteristics of our LUT-based architecture are reasonably similar to those of the commercial counterpart. Then, we compare the AIC architecture to the baseline on a number of benchmarks, and we find a few difficulties that had been overlooked before. We thus explore other design possibilities around the original design point and show their detailed impact. Finally, we discuss how the very structure of current logic clusters seems not perfectly appropriate for getting the best out of AICs and conclude that, even though they are not confirmed as an immediate blessing today, AICs still offer rich research opportunities.