Synthesis of LUT Networks for Random-Looking Dense Functions with Don't Cares - Towards Efficient FPGA Implementation of DNN

Yukio Miyasaka, Alan Mishchenko, John Wawrzynek, Nicholas J. Fraser

Abstract: Many EDA applications deal with logic functions representing complex mathematical computations. Although in many cases, these functions depend on a small number of inputs, they often resemble random functions, making it hard to synthesize them using the traditional methods based on SOP minimization. This paper describes efficient synthesis and LUT mapping for this class of functions using a novel method that implements BDD-based minimization based on truth tables. The paper also investigates optimization with don't cares, when the outputs of a function are unspecified for some inputs, which is particularly useful in machine learning applications that trade accuracy for area. Compared to optimization and mapping used in academic and industrial tools, our method works faster and results in 1.5x smaller networks, while extra 20% area reduction was possible with don't cares at almost no accuracy cost.