A synthesis oriented omniscient manual editor

Abstract

The cost functions used to evaluate logic synthesis transformations for FPGAs are far removed from the final speed and routability determined after placement, routing and timing analysis. This distance has given rise to the field of physical synthesis, which attempts to improve logic synthesis by employing cost functions that contain placement, routing and/or timing analysis information.In this work we take this notion to an extreme that we call omniscience, in which post-routing timing analysis is provided in the context of a manual editor in which the user selects logical and physical transformations. After each incremental circuit modification, the user is informed of the circuit performance after routing and timing analysis. Since the computations involved in providing this level of information are large, we restrict the application to relatively small circuits, no larger than 1000 logic elements.Using this approach on a commercial FPGA, we propose a set of logic transformations specific to the logic and routing architecture of the Xilinx Virtex-E device. On a set of 10 circuits we have achieved an average performance improvement of 10% when both logical and physical changes are used. Another value of the editor is that it reveals new types of automatable physicalsynthesis transformations and optimization strategies that arise from architectural properties of the target device.