Toward accurate models of achievable routing

Models of achievable routing, i.e., chip wireability, rely on estimates of available and required routing resources. Required routing resources are estimated from placement or (a priori) using wire length estimation models. Available routing resources are estimated by calculating a nominal "supply" then take into account such factors as the efficiency of the router and the impact of vias. Models of achievable routing can be used to optimize interconnect process parameters for future designs or to supply objectives that guide layout tools to promising solutions. Such models must be accurate in order to be useful and must support empirical verification and calibration by actual routing results. In this paper, we discuss the validation of such models and we apply our validation process to three existing models. We find notable inaccuracies in the existing models when matched against real data. We then present a thorough analysis of the assumptions underlying these models. Based on this analysis, we discuss requirements for predictors of routing resources and make suggestions for a new model of achievable routing.