Zhe-Wei Jiang

NTUplace3: An Analytical Placer for Large-Scale Mixed-Size Designs With Preplaced Blocks and Density Constraints

In addition to wirelength, modern placers need to consider various constraints such as preplaced blocks and density. We propose a high-quality analytical placement algorithm considering wirelength, preplaced blocks, and density based on the log-sum-exp wirelength model proposed by Naylor and the multilevel framework. To handle preplaced blocks, we use a two-stage smoothing technique, i.e., Gaussian smoothing followed by level smoothing, to facilitate block spreading during global placement (GP). The density is controlled by white-space reallocation using partitioning and cut-line shifting during GP and cell sliding during detailed placement. We further use the conjugate gradient method with dynamic step-size control to speed up the GP and macro shifting to find better macro positions. Experimental results show that our placer obtains very high-quality results.

A high-quality mixed-size analytical placer considering preplaced blocks and density constraints

In addition to wirelength, modern placers need to consider various constraints such as preplaced blocks and density. We propose a high-quality analytical placement algorithm considering wirelength, preplaced blocks, and density based on the log-sum-exp wirelength model proposed by Naylor et al. (2001) and the multilevel framework. To handle preplaced blocks, we use a two-stage smoothing technique, Gaussian smoothing followed by level smoothing, to facilitate block spreading during global placement. The density is controlled by white-space re-allocation using partitioning and cut-line shifting during global placement and cell sliding during detailed placement. We further use the conjugate gradient method with dynamic step-size control to speed up the global placement and macro shifting to find better macro positions. Experimental results show that our placer obtains the best published results

NTUplace: a ratio partitioning based placement algorithm for large-scale mixed-size designs

In this paper, we present a hierarchical ratio partitioning based placement algorithm for large-scale mixed-size designs. The placement algorithm consists of three steps: global placement, legalization,and detailed placement; it works in a hierarchical manner and integrates net-weighting partitioning, whitespace management, look-ahead bipartitioning, and fast legalization to handle the large-scale mixed-size placement problems. Unlike the traditional partitioning-based technique that is based on balanced partitioning, we apply ratio partitioning in each level. Further, applying the look-ahead bipartitioning technique in each level, we can evaluate the feasibility of the placement for sub-partitions more accurately. Therefore, we can find better ratios for the partitions, leading to easier legalization for the global placement result and finally a better detailed placement solution. Experimental results show the efficiency and effectiveness of our algorithm.

Routability-driven analytical placement by net overlapping removal for large-scale mixed-size designs

Routability is a challenging cost metric for modern large-scale mixed-size placement. Most existing routability-driven placement algorithms apply whitespace allocation to relieve the routing congestion. Nevertheless, we observe that whitespace allocation might worsen the routability of a placement. To remedy this deficiency, we propose in this paper a new direction/technique, called net overlapping removal, to optimize the routability during placement. Unlike most previous works that allocate whitespace among blocks, our approach moves nets apart from congested regions to improve the chip routability. To apply the net overlapping removal technique, we generalize a net bounding-box based congestion evaluation model to handle practical routing constraints and speed up the routability optimization during placement. We further propose a Gaussian smoothing technique to handle the challenging macro porosity issue, arising in modern mixed-size designs with large macros that require to preserve routing resources for inner routing of the macros. Experimental results show that our approaches lead to significantly better routability and running time than previous works for mixed-size placement.

Essential Issues in Analytical Placement Algorithms

The placement problem is to place objects into a fixed die such that no objects overlap with each other and some cost metric (e.g., wirelength) is optimized. Placement is a major step in physical design that has been studied for several decades. Although it is a classical problem, many modern design challenges have reshaped this problem. As a result, the placement problem has attracted much attention recently, and many new algorithms have been developed to handle the emerging design challenges. Modern placement algorithms can be classified into three major categories: simulated annealing, min-cut, and analytical algorithms. According to the recent literature, analytical algorithms typically achieve the best placement quality for large-scale circuit designs. In this paper, therefore, we shall give a systematic and comprehensive survey on the essential issues in analytical placement. This survey starts by dissecting the basic structure of analytical placement. Then, various techniques applied as components of popular analytical placers are studied, and two leading placers are exemplified to show the composition of these techniques into a complete placer. Finally, we point out some research directions for future analytical placement.

NTUplace2: a hybrid placer using partitioning and analytical techniques

In this paper, we present a hybrid placer, called NTUplace2, which integrates both the partitioning and the analytical (quadratic programming) placement techniques for large-scale mixed-size designs. Unlike most existing placers that minimize wirelength alone, we also control the cell density to optimize routability while minimizing the total wirelength. NTUplace2 consists of three major stages: multilevel global placement, legalization, and detailed placement. To handle mixed-size designs, in particular, we present a linear programming based legalization algorithm to remove overlaps between macros during global placement. Various other techniques are integrated to improve the solution quality at every stage.

An Optimal Network-Flow-Based Simultaneous Diode and Jumper Insertion Algorithm for Antenna Fixing

As technology enters the nanometer territory, the antenna effect plays an important role in determining the yield and reliability of a VLSI circuit. Diode and jumper insertions are the most effective techniques to fix the antenna effect. However, due to the increasing design complexity and the limited routing resource, applying diode or jumper insertion alone cannot achieve a high antenna fixing rate. In this paper, we give a polynomial-time antenna violation detection/fixing algorithm by simultaneous diode and jumper insertion with minimum cost, which is based on a minimum-cost network-flow formulation. Experimental results show that our algorithm consistently achieves much higher antenna fixing rates than the state-of-the-art jumper and diode insertion algorithms alone.

Challenges and solutions in modern analog placement

The analog placement problem is to place devices without overlap and design-rule-correction (DRC) error under position constraints (e.g. symmetry, cluster) such that some cost metric (e.g. area, wirelength) is optimized. However, modern analog design challenges have reshaped the placement problem. A modern analog placer also needs to consider device layout-dependent-effect (LDE) and interconnect parasitic effect. Because of multiple objectives, it is impossible to decide the single best placement. In this paper, we first introduce our placer that can explore multiple placements under position constraints so that a designer can analyze the trade-off among different objectives. Then, we provide some future research directions for the modern analog placement problem.

An optimal simultaneous diode/jumper insertion algorithm for antenna fixing

As technology enters the nanometer territory, the antenna effect plays an important role in determining the yield and reliability of a VLSI circuit. Diode insertion and jumper insertion are the most effective techniques to fix the antenna effect. However, due to the increasing design complexity and the limited routing resource, applying diode or jumper insertion alone cannot achieve a high antenna fixing rate. In this paper, we give a polynomial-time antenna violation detection/fixing algorithm by simultaneous diode/jumper insertion with minimum cost, based on a minimum-cost network-flow formulation. Experimental results show that our algorithm consistently achieves much higher antenna fixing rates than the state-of-the-art jumper insertion and diode insertion algorithms alone