Zero Skew Clock Routing ECE 556 Project Proposal John Thompson Kurt Ting Simon Wong

Overview Problem definition Nearest neighbor Zero-skew tree construction Algorithm Benchmarks

Problem Definition Given a set S of sink locations, and given a connection topology G, construct a zero skew clock tree T(S) with topology G and having minimum cost…

Nearest Neighbor Use Delaunay Triangulation to find the pair of points with shortest separating distance. These are the points that will be connected next…

Delaunay Triangulation A Delaunay triangulation of a vertex set is a triangulation of the vertex set with the property that no vertex in the vertex set falls in the interior of the circumcircle (circle that passes through all three vertices) of any triangle in the triangulation.

Delaunay Triangulation Original vertex set Delaunay Triangulation

Delaunay Triagulation Dual of Voronoi Diagram

Voronoi Diagram N is the set of all sites S. The Voronoi polygon vor(S) of a site S  N is defined to be the region consisting of the points in R d whose nearest neighbor in N is S. Voronoi Diagram is the set of all vor(S). Vor(S)

Construction of Vonoroi Diagram Partition N into subsets N 1, N 2 of equal sizes by median x-coordinates

Construction of Vonoroi Diagram Construct Vor(N 1 ) and Vor(N 2 ) recursively

Construction of Vonoroi Diagram Construct Vor(N 1 ) and Vor(N 2 ) recursively

Construction of Vonoroi Diagram Construct dividing chain

Construction of Vonoroi Diagram Discard all edges of Vor(N 2 ) that lie to the left of dividing line, and the same for Vor(N 1 ) The result is Vor(N) is the Voronoi Diagram of the entire set

Approximation of Manhattan Segments Use n points on a Manhattan Segment to represent it in Delaunay Triagulation

Zero-Skew Tree Construction Use a clustering-based optimization algorithm Algorithm steps  Find center  Embedding  Local Embedding

CL Find Center Step 1:  K := S Step 2:  Stop once the root node has been reached. Otherwise, construct the nearest-neighbor graph G(K,E) on K, and sort edges in E by their weights in non-decreasing order. Step 3:  Take the smallest weight edge (v 1, v 2 ) from E, and delete the edge from E. Calculate segment for v from v1, v2. Delete v1, v2 from K, add v to K. If the capacitance of a subtree becomes too large, insert a buffer…

CL Find Center Pick K pairs of Near Neighbor for Manhattan Segment Calculation

Calculating Manhattan Segments Three cases  From two points  From a point and a segment  From two segments The general case is from two segments

Manhattan Segment Construction from Two Parallel Manhattan Segments

Manhattan Segment Construction from Two Perpendicular Manhattan Segments

Merging Segments Manhattan Segments after Find Center Segments after merging

Simple Buffer Insertion Heuristic

Embedding Step 1:  Determine the center v c on the segment for v c by selecting the nearest point to the root v r. Route from v r to v c. Step 2:  Local embedding on v c …

Embedding Manhattan Segments after Find Center Determine Center Vc From Vr VCVC VRVR

Local Embedding Step 1:  If v has no child, return… Step 2:  Let v 1 and v 2 be children of v. Then determine the point v i on the segment for v i so as to satisfy the zero- skew merge equations. Route from v to v i … Step 3:  Perform local embedding on v 1 and v 2 …

Embedding Local Embedding for V C & remaining segments Final Routing Tree VCVC VRVR VRVR

Benchmarks UCLA MCNC clock benchmark 1.0 suite  Originally from Jackson’s (et al.) “Clock routing for high performance ICs” paper… UCLA IBM clock benchmark 1.0 suite  Originally R. S. Tsay’s benchmarks used in his “Exact zero skew” paper… UCLA ISCAS clock benchmark 1.0

References Masato Edahiro; “A Clustering-Based Optimization Algorithm in Zero-Skew Routings”; 1993 Ting-Hai Chao, Yu-Chin Hsu, and Jan-Ming Ho; “Zero Skew Clock Net Routing”; 1992 Ting-Hai Chao, Yu-Chin Hsu, Jan-Ming Ho, and Kenneth D. Boese; “Zero Skew Clock Routing with Minimum Wirelength”; 1992 Yu Chen, Andrew B. Kahng, Gang Qu, and Alexander Zelikovsky; “The Associative-Skew Clock Routing Problem”; 1999