InTime: A Machine Learning Approach for Efficient Selection of FPGA CAD Tool Parameters

Abstract

FPGA CAD tool parameters controlling synthesis optimizations, place and route effort, mapping criteria along with user-supplied physical constraints can affect timing results of the circuit by as much as 70% without any change in original source code. A correct selection of these parameters across a diverse set of benchmarks with varying characteristics and design goals is challenging. The sheer number of parameters and option values that can be selected is large (thousands of combinations for modern CAD tools) with often conflicting interactions. In this paper, we present InTime, a machine-learning approach supported by a cloud-based (or cluster-based) compilation infrastructure for automating the selection of these parameters effectively to minimize timing costs. InTime builds a database of results from a series of preliminary runs based on canned configurations of CAD options. It then learns from these runs to predict the next series of CAD tool options to improve timing results. Towards the end, we rely on a limited degree of statistical sampling of certain options like placer and synthesis seeds to further tighten results. Using our approach, we show 70% reduction in final timing results across industrial benchmark problems for the Altera CAD flow. This is 30% better than vendor-supplied design space exploration tools that attempts a similar optimization using canned heuristics.