A novel fixed-outline floorplanner with zero deadspace for hierarchical design

ABSTRACT Fixed-outline floorplanning, which enables hierarchical design, is considered more and more important nowadays. In this paper, a novel SA-based Fixed-outline Floorplanner with the Optimal Area utilization named SAFFOA is introduced to improve the total wirelength. The basic idea is to build and solve a group of four quadratic equations in four variables iteratively, which can handle the fixed-outline constraint of any aspect ratio. A new topological representation called Ordered Quadtree is then custom-made for this basic idea to facilitate its integration into SA iterations. After the fixed-outline constraint with 100% area utilization is achieved, we will solve the tradeoff between the chip area and wirelength and thus concentrate on the latter in SA process. Experimental results show that the chip wirelength is decreased by about 16.8% and 8.6% on average, compared with two previous fixed-outline floorplanners on soft modules, which are both proved to be better than Parquet. Besides, our method is still competitive on the wirelength, even if compared with some leading-edge outline-free floorplanners. At last, Local Refinement is also adopted to guide the SA process and reshape soft modules to meet the constraint on their aspect ratios (ARs). With its help, SAFFOA can still generate feasible floorplans with no deadspace under a strict AR constraint such as 0.5, 2

Floorplan-guided placement for large-scale mixed-size designs

In the nanometer scale era, placement has become an extremely challenging stage in modern Very-Large-Scale Integration (VLSI) designs. Millions of objects need to be placed legally within a chip region, while both the interconnection and object distribution have to be optimized simultaneously. Due to the extensive use of Intellectual Property (IP) and embedded memory blocks, a design usually contains tens or even hundreds of big macros. A design with big movable macros and numerous standard cells is known as mixed-size design. Due to the big size difference between big macros and standard cells, the placement of mixed-size designs is much more difficult than the standard-cell placement. This work presents an efficient and high-quality placement tool to handle modern large-scale mixed-size designs. This tool is developed based on a new placement algorithm flow. The main idea is to use the fixed-outline floorplanning algorithm to guide the state-of-the-art analytical placer. This new flow consists of four steps: 1) The objects in the original netlist are clustered into blocks; 2) Floorplanning is performed on the blocks; 3) The blocks are shifted within the chip region to further optimize the wirelength; 4) With big macro locations fixed, incremental placement is applied to place the remaining objects. Several key techniques are proposed to be used in the first two steps. These techniques are mainly focused on the following two aspects: 1) Hypergraph clustering algorithm that can cut down the original problem size without loss of placement Quality of Results (QoR); 2) Fixed-outline floorplanning algorithm that can provide a good guidance to the analytical placer at the global level. The effectiveness of each key technique is demonstrated by promising experimental results compared with the state-of-the-art algorithms. Moreover, using the industrial mixed-size designs, the new placement tool shows better performance than other existing approaches