AppAxO: Designing Application-specific Approximate Operators for FPGA-based Embedded Systems

Approximate arithmetic operators, such as adders and multipliers, are increasingly used to satisfy the energy and performance requirements of resource-constrained embedded systems. However, most of the available approximate operators have an application-agnostic design methodology, and the efficacy of these operators can only be evaluated by employing them in the applications. Furthermore, the various available libraries of approximate operators do not share any standard approximation-induction policy to design new operators according to an application’s accuracy and performance constraints. These limitations also hinder the utilization of machine learning models to explore and determine approximate operators according to an application’s requirements. In this work, we present a generic design methodology for implementing FPGA-based application-specific approximate arithmetic operators. Our proposed technique utilizes lookup tables and carry-chains of FPGAs to implement approximate operators according to the input configurations. For instance, for an \(\text{M}\times \text{N}\) accurate multiplier utilizing K lookup tables, our methodology utilizes K-bit configurations to design \(2^K\) approximate multipliers. We then utilize various machine learning models to evaluate and select configurations satisfying application accuracy and performance constraints. We have evaluated our proposed methodology for three benchmark applications, i.e., biomedical signal processing, image processing, and ANNs. We report more non-dominated approximate multipliers with better hypervolume contribution than state-of-the-art designs for these benchmark applications with the proposed design methodology.