VLSI Placement and Routing: The PI Project

This book provides a superb introduction to and overview of the MIT PI System for custom VLSI placement and routing. Alan Sher­ man has done an excellent job of collecting and clearly presenting material that was previously available only in various theses, confer­ ence papers, and memoranda. He has provided here a balanced and comprehensive presentation of the key ideas and techniques used in PI, discussing part of his own Ph. D. work (primarily on the place­ ment problem) in the context of the overall design of PI and the contributions of the many other PI team members. I began the PI Project in 1981 after learning first-hand how dif­ ficult it is to manually place modules and route interconnections in a custom VLSI chip. In 1980 Adi Shamir, Leonard Adleman, and I designed a custom VLSI chip for performing RSA encryp­ tion/decryption [226]. I became fascinated with the combinatorial and algorithmic questions arising in placement and routing, and be­ gan active research in these areas. The PI Project was started in the belief that many of the most interesting research issues would arise during an actual implementation effort, and secondarily in the hope that a practically useful tool might result. The belief was well-founded, but I had underestimated the difficulty of building a large easily-used software tool for a complex domain; the PI soft­ ware should be considered as a prototype implementation validating the design choices made.