Yi-Lin Chuang

Constraint graph-based macro placement for modern mixed-size circuit designs

In this paper, we propose a constraint graph-based macro placement algorithm that removes macro overlaps and optimizes macro positions for modern mixed-size circuit designs. Improving over the constraint graph by working only on its essential edges without loss of the solution quality, our algorithm can search for high-quality macro placement solutions effectively and efficiently. Instead of packing macros along chip boundaries like most recent previous work, our placer can determine a non-compacted macro placement by linear programming and placement region cost evaluation and handle various placement constraints/objectives. Compared with various leading academic macro placers, our algorithm can consistently and significantly reduce the wirelengths for designs with different utilization rates, implying that our macro placer is robust and has very high quality.

Pulsed-latch aware placement for timing-integrity optimization

Utilizing pulsed-latches in circuit designs is one emerging solution to timing improvements. Pulsed-latches, driven by a brief clock signal generated from pulse generators, possess superior design parameters over flip-flops. If the pulse generator and pulsed-latches are not placed properly, however, pulse-width degradations at pulsed-latches and thus timing violations might occur. In this paper, we present a unified placement framework for pulsed-latches to maintain the timing integrity. Our new placer has the following distinguished features: 1) a multilevel analytical placement framework to effectively prevent the potential pulse-width distortion problem; 2) a physical-location aware pulse-generator insertion algorithm to identify each desired group of a pulse generator and latches; and 3) a new optimization gradient for global placement to consider the impact of load capacitance of generators. Experimental results show that our placement flow can effectively consider pulse-width integrity and thus achieve much smaller total/worst negative slacks with marginal wirelength overheads, compared to a leading commercial and an academic placement flows.

Design-hierarchy aware mixed-size placement for routability optimization

Routability is a mandatory metric for modern large-scale mixed-size circuit placement which typically needs to handle hundreds of large macros and millions of small standard cells. However, most existing academic mixed-size placers either focus on wirelength minimization alone, or do not consider the impact of movable macros on routing. To remedy these insufficiencies, this paper formulates design-hierarchy information as a novel fence force in an analytical placement framework. Unlike a state-of-the-art routability-driven placer that simply removes net bounding boxes during placement, this paper utilizes two different optimization forces, the global fence force and the local spreading force, to determine the positions of both standard cells and macros. We utilize design-hierarchy information to determine block distributions globally, and locally we add additional spreading forces to preserve sufficient free space among blocks by a net-topology estimation. With the interactions between these two forces, our placer can well balance routability and wirelength. Experimental results show that our placer can achieve the best routability and routing time among all published works.

Statistical thermal modeling and optimization considering leakage power variations

Unaddressed thermal issues can seriously hinder the development of reliable and low power systems. In this paper, we propose a statistical approach for analyzing thermal behavior under leakage power variations stemming from the manufacturing process. Based on the proposed models, we develop floorplanning techniques targeting thermal optimization. The experimental results show that peak temperature is reduced by up to 8.8°C, while thermal-induced leakage power and maximum thermal variance are reduced by 13% and 17%, respectively, with no additional area overhead compared with best performance-driven optimized design.

Pulsed-latch-based clock tree migration for dynamic power reduction

Minimizing the clock tree has been known as an effective approach to reduce power dissipation in modern circuit designs. However, most existing power-aware clock tree synthesis algorithms still focus on optimizing power in flip-flops, which might have limited power savings. In this work, we explore the pulsed-latch utilization in clock tree synthesis for further power savings. We are the first work in the literature to propose a novel synthesis algorithm to efficiently migrate a flip-flop-based clock tree into a pulsed-latch one. To maintain performance of a clock tree while considering load balance (skew issues) simultaneously, we determine the clock tree topology by the minimum-cost maximum-flow network. Experimental results show that our algorithm can further reduce power consumption by 22% on average compared to approaches without pulsed latches. Categories and Subject Descriptors: B.7.2 [Integrated Circuits]: Design Aids General Terms: Algorithms, Design

Pulsed-Latch Utilization for Clock-Tree Power Optimization

Minimizing the size of a clock tree is known as an effective approach to reduce power dissipation in modern circuit designs. However, most existing power-aware clock-tree minimization algorithms optimize power on the basis of flip-flops alone, which may result in limited power savings. To achieve a power and timing tradeoff, this paper investigates the pulsed-latch utilization in a clock tree for further power savings. This is the first paper to propose a migration approach to efficiently construct a clock tree with both pulsed-latches and flip-flops. The proposed method is based on minimum-cost maximum-flow formulation to globally determine the tree topology, which maintains load balance and considers the wirelength between pulse generators and pulsed latches. Experimental results indicate that the proposed migration approach can improve the power consumption by 12% and 13% with 7% and 70% skew improvements on average compared with the most recent paper on the industrial circuits and ISPD-2010 benchmarks, respectively.

Voltage-drop aware analytical placement by global power spreading for mixed-size circuit designs

Excessive supply voltage drops in a circuit may lead to significant circuit performance degradation and even malfunction. To handle this problem, existing power delivery aware placement algorithms model voltage drops as an optimization objective. We observe that directly minimizing the voltage drops in the objective function might not resolve voltage-drop violations effectively and might cause problems in power-integrity convergence. To remedy this deficiency, in this paper, we propose new techniques to incorporate device power spreading forces into a mixed-size analytical placement framework. Unlike the state-of-the-art previous work that handles the worst voltage-drop spots one by one, our approach simultaneously and globally spreads all the blocks with voltage-drop violations to desired locations directly to minimize the violations. To apply the power force, we model macro current density and power rails for our placement framework to derive desired macro/cell locations. To further improve the solution quality, we propose an efficient mathematical transformation to adjust the power force direction and magnitude. Experimental results show that our approach can substantially improve the voltage drops, wirelength, and runtime over the previous work.

PRICE: power reduction by placement and clock-network co-synthesis for pulsed-latch designs

Pulsed latches have emerged as a popular technique to reduce the power consumption and delay for clock networks. However, the current physical synthesis flow for pulsed latches still performs circuit placement and clock-network synthesis separately, which limits achievable power reduction. This paper presents the first work in the literature to perform placement and clock-network co-synthesis for pulsed-latch designs. With the interplay between placement and clock-network synthesis, the clock-network power and timing can be optimized simultaneously. Novel progressive network forces are introduced to globally guide the placer for iterative improvements, while the clock-network synthesizer makes use of updated latch locations to optimize power and timing locally. Experimental results show that our framework can substantially minimize power consumption and improve timing slacks, compared to existing synthesis flows.

Effective Wire Models for X-Architecture Placement

In this paper, we derive the X-half-perimeter wirelength (XHPWL) model for X-architecture placement and explore the effects of three different wire models on X-architecture placement, including the Manhattan-half-perimeter wirelength (MHPWL) model, the XHPWL model, and the X-Steiner wirelength (XStWL) model. For min-cut partitioning placement, we apply the XHPWL and XStWL models to the generalized net-weighting method that can exactly model the wirelength after partitioning by net weighting. For analytical placement, we smooth the XHPWL function using log-sum-exp functions to facilitate analytical placement. This paper shows that both the XHPWL and XStWL models can reduce the X wirelength effectively. In particular, our results reveal the effectiveness of the X architecture on wirelength reduction during placement and, thus, the importance of the study on the X-placement algorithms, which is different from the results given in the work of Ono et al. which suggests that the X-architecture placement might not improve the X-routing wirelength over the Manhattan-architecture placement.

Pulsed-Latch Aware Placement for Timing-Integrity Optimization

Utilizing pulsed-latches in circuit designs is one emerging solution to timing improvements. Pulsed-latches, driven by a brief clock signal generated from pulse generators, possess superior design parameters over flip-flops. If the pulse generator and pulsed-latches are not placed properly, however, pulse-width degradations at pulsed-latches and thus timing violations might occur. In this paper, we present a unified placement framework for pulsed-latches to maintain the timing integrity. Our new placer has the following distinguished features: 1) a multilevel analytical placement framework to effectively prevent the potential pulse-width distortion problem; 2) a physical-location aware pulse-generator insertion algorithm to identify each desired group of a pulse generator and latches; and 3) a new optimization gradient for global placement to consider the impact of load capacitance of generators. Experimental results show that our placement flow can effectively consider pulse-width integrity and thus achieve much smaller total/worst negative slacks with marginal wirelength overheads, compared to a leading commercial and an academic placement flows.