A place and route aware buffered Steiner tree construction

Abstract

In order to achieve timing closure on increasingly complex IC designs, buffer insertion needs to be performed on thousands of nets within an integrated physical synthesis system. In most of previous works, buffers may be inserted at any open space. Even when there may appear to be space for buffers in the alleys between large blocks, these regions are often densely packed or may be useful later to fix critical paths. In addition, a buffer solution may inadvertently force wires to go through routing congested regions. Therefore, within physical synthesis, a buffer insertion scheme needs to be aware of both placement congestion and routing congestion of the existing layout and so it has to be able to decide when to insert buffers in dense regions to achieve critical performance improvement and when to utilize the sparser regions of the chip. With the proposed Steiner tree adjustment technique, this work aims at finding congestion-aware buffered Steiner trees. Our tree adjustment technique takes a Steiner tree as input, modifies the tree and simultaneously handles the objectives of timing, placement and routing congestion. To our knowledge, this is the first study, which simultaneously considers these three objectives for the buffered Steiner tree problem. Experimental results confirm the effectiveness of our algorithm while it achieves up to 20x speed-up when comparing with the state-of-the-art algorithm (C.J. Alpert et al., 2003).