Analytical Model for Relating FPGA Logic and Routing Architecture Parameters to Post-Routing Wirelength

Abstract

Analytical models have been introduced for rapidly evaluating the impact of architectural design choices on FPGA performance through model-based trend analysis. Modeling wirelength is a critical problem since channel width can be expressed as a function of total net length in a design, which is an indicator of routability for an FPGA. Furthermore, performance indicators, such as critical path delay and power consumption, are functions of net capacitance, which in turn is a function of net length. The analytical models to this date mainly originate from extracting circuit characteristics from post-placement stage of the CAD flow, which instills a strong binding between the model and the optimization objective of the CAD flow. Furthermore, these models primarily take only logic architecture features into account. In this study, we present a post-routing wirelength model that takes into account both logic and routing architectural parameters, and that does not rely on circuit characteristics extracted from any stage of the FPGA CAD flow. We apply a methodological approach to model parameter tuning as opposed to relying on a curve-fitting method, and show that our model accurately captures the experimental trends in wirelength with respect to changes in logic and routing architecture parameters individually. We demonstrate that the model accuracy is not sacrificed even if the performance objective of the CAD flow changes or the algorithms used by individual stages of the CAD flow (technology mapping, clustering, and routing) change. We swap the training and validation benchmarks, and show that our model development approach is robust and the model accuracy is not sacrificed. We evaluate our model based on new set of benchmarks that are not part of the training and validation benchmarks, and demonstrate its superiority over the state of the art. Based on the swapping based experiments, we show that the model parameters take values in a fixed range. We verify that this range holds its validity even for benchmarks that are not part of the training and validation benchmarks. We finally show that our model maintains a good estimation of the empirical trends even when very large values are used for the logic block architecture parameter.