in a design flow a constraint is addressed, the more flexibility there is to address the constraint. Ironically, the earlier one is in a design flow, the more difficult it is to predict compliance. For example, an architectural decision to pipeline a logic function can have a far greater impact on total chip performance than any amount of postrouting fix-up. At the same time, accurately predicting the performance impact of such a change before the chip logic is synthesized, let alone placed or routed, is very difficult. This paradox has shaped the evolution of the design closure flow in several ways. First, it requires that the design flow is no longer composed of a linear set of discrete steps. In the early stages of VLSI it was sufficient to break the design into discrete stages, i.e., first do logic synthesis, then do placement, then do routing. As the number and complexity of design closure constraints has increased, the linear design flow has broken down. In the past if there were too many timing constraint violations left after routing, it was necessary to loop back, modify the tool settings slightly, and reexecute the previous placement steps. If the constraints were still not met, it was necessary to reach further back in the flow and modify the chip logic and repeat the synthesis and placement steps. This type of looping is both time consuming and unable to guarantee convergence i.e., it is possible to loop back in the flow to correct one constraint violation only to find that the correction induced another unrelated violation. See also Timing closure Electronic design automation Design flow (EDA) Integrated circuit design References Electronic Design Automation For Integrated Circuits Handbook, by Lavagno, Martin, and Scheffer, A survey of the field of electronic design automation. In particular, this article is derived (with permission) from the introduction of Chapter 10, Volume II, Design Closure by John Cohn. Electronic design Electronic design automation Electronic engineering Electronics optimization