Packing Floorplan Representations

As technology advances, design complexity is increasing and the circuit size is getting larger. To cope with the increasing design complexity, hierarchical design and IP modules are widely used. This trend makes module floorplanning/placement much more critical to the quality of a VLSI design than ever. A fundamental problem to floorplanning/placement lies in the representation of geometric relationship among modules. The representation profoundly affects the operations of modules and the complexity of a floorplan/placement design process. It is thus desired to develop an efficient, flexible, and effective representation of geometric relationship for floorplan/placement designs. Many floorplan representations have been proposed in the literature. We can represent a floorplan as a rectangular dissection of the floorplan region, and classify the representations based on the floorplan structures that the representations can model. Preceding chapters have covered the slicing structure [16,19] which can be obtained by repetitively subdividing rectangles horizontally or vertically into smaller rectangles, and the mosaic structure [4] for which the floorplan region is dissected into rooms so that each room contains exactly one module. The mosaic structure is more general than the slicing structure in the sense that the former can model more floorplan structures. This chapter focuses on the representations for the packing structure, the most general floorplan representation which can model a floorplan with empty rooms. There is a special type of the packing structure, the compacted structure, for which modules are compacted to some corner of the floorplan region, say the bottom-left corner, and no module can further be shifted down or left. The compacted structure induces much smaller solution spaces than the general one. Unlike the general packing representation which can fully model the topological relationship among modules [8, 9, 14, 15, 25], however, the compacted packing representations [1, 3, 12] can model only partial topological information, and thus the module dimensions are required in order to construct an exact floorplan. In this chapter, we shall detail the modelling, properties, and operations of the popular packing floorplan representations in the literature: compacted floorplan representations such as O-tree, B*-tree, and Corner Sequence (CS), and general packing ones such as Sequence Pair (SP) [14], Bounded Sliceline Grid (BSG), Transitive Closure Graph (TCG), Transitive Closure Graph with a Sequence (TCG-S), and Adjacent Constraint Graph (ACG) [25].