Custom design, in which the designer controls the physical structure of the chip, can greatly improve the speed, power, and delay of an ASIC chip without affecting design time. Through floorplanning and tiling data paths, the designer places the critical wires first, before the logic is placed. Crafted datapath cells structure wiring at the other end of the spectrum by keeping local wires short enabling the use of minimum sized drivers. Routing the wires first gives early visibility of timing issues, allows the design to be optimized to drive the exact wire load, and enables the use of fast circuit styles.
William J. Dally, Andrew Chang