VLSI时钟布线算法的研究进展

随着集成电路工艺技术进入深亚微米、超深亚微米阶段，时钟频率已达到数GHz。设计一个高速、零偏差、低功耗的时钟布线算法已成为一项紧要的任务。文章简要介绍了时钟布线算法的研究进展，包括拓扑生成、实体嵌入、缓冲器插入和变线宽优化等各个阶段的各种算法，并指出了目前这些算法存在的一些问题。     

一种有效的变线宽时钟布线算法

针对时钟布线提出了一种有效的变线宽算法。该算法通过对时钟树中各树枝延迟敏感度的分析,选择总体最优的连线进行变线宽处理,使得时钟树的路径延迟最小化。在延迟优化后,为了使时钟偏差小于给定的约束,通过变线宽对各种钟汇点的延迟进行全面的再分配,使延迟最大的时钟汇点延迟最小化,而延迟较小的路径延迟适当增加,以进一步改善时钟树延迟。实验结果表明,该算法有较高的运行效率,时钟树的路径路径和时钟偏差得到了显著的改     

基于动态网格的135度PCB区域布线算法

由于不断增长的芯片引脚数量、极高的引脚密度和独特的物理限制,印刷电路板(Printed Circuit Board,PCB)的手动布线已成为一项耗时的任务。近年来,高效率的自动化布线技术得到了广泛的研究。区域布线是PCB设计的一个重要组成部分。针对基于静态网格区域布线的方案,布线拥塞、布通率低等问题,本文提出了一套基于动态网格的135度区域布线算法,主要包括以下技术:(1)对当前布线采用实时扩展动态网格;(2)135度布线角度节点调整算法;(3)基于拥塞控制的改进A^*算法;(4)有效的拆线重布机制。实验结果表明,该算法对于所有工业界布线测试用例布通率都达到100%,并且运行时间方面优于工业布线器Free Routing和Allegro。     

电子整机三维自动布线技术研究

电子整机的快速布线是影响整机快速制造的瓶颈之一。本文采用三维加权网格,对电子整机三维模型进行网格划分,描述了布线空间。运用基于网格的迷宫算法和最小斯坦纳树生成法,进行线缆敷设的线路搜索,并加入Rubin优化算法改善搜索速度。结合实际工程经验和规则,以自行开发的电子整机三维布线系统(3DRS)验证了该算法的可行性。     

时延驱动的整平面整体布线算法

本文结出了一个新的时延驱动的整体布线算法．算法采用了整平面布线技术，从而具有快速求解的特点且无网序问题的困扰．算法优化的目标是使所有线网的最大时延之和最小，尤其是在关键路径上的线网实际电路的布线结果表明该算法可有效地改善关键路径上线网的时延．     

基于形状的朝向目标布线算法

在传统布线算法的基础上,本文提出了一种无网格布线算法——基于形状的朝向目标线探索法.该布线算法主要针对障碍物外形尺寸多样,已布连线线宽及线间距离可变的布线情况,尤其适用于印刷电路板及集成电路的布线,该算法的基本要素是障碍物的包容矩形和带有预定终点的探索线,且所需存储空间小、布线速度快、布线路径短,具有良好的布线效果.     

多层无网格布线算法研究进展

本文以通道布线、区域详细布线和整个面向区域的布线方法为序,介绍了近十年提出的无网格布线算法,在对各算法进行深入分析的基础上,给出了一些有益的结论,并提出了进一步工作的方向.     

基于蚁群算法的集成电路无网格布线

蚁群算法[1]作为一种较新的进化类方法,目前已经在若干领域取得了成功的应用,诸如：旅行商问题、二次分配问题、通讯网络中的路由问题以及负载平衡问题、大规模集成电路设计等。本文提出了一种基于蚁群算法的集成电路无网格布线算法。对于给定的布线平面,该算法首先由障碍图形和各个线网的端点生成一个包含最短路径的访问点阵,建立初始信息索矩阵,然后利用蚁群算法所特有的路径寻优功能来找到当前布线路径上的最短路径。同时本文在路径搜索过程中引入了引力的概念,使得蚁群在引力的作用下以较快的速度找到目标端点。     

一种新的无网格拆线重布算法

结合无网格布线的特点,提出一种新的无网格拆线重布算法.该算法显式地表示并动态更新线网所属区域的拥挤程度.在拆线重布进行待布线网的路径搜索时,每个扩展节点中增加拆除线网周边的拥挤权重,从而将待布线网的路径搜索过程和拆除线网的选择过程统一起来,有效地提高了被拆除线网重新布通的可能性.该算法利用改进的二叉区间树有效组织中间数据,降低计算的复杂度.实验结果表明,该算法能有效消除布线顺序对布线结果的影响,提高布通率,且算法运行速度较快.     

一种新的无网格拆线重布算法

结合无网格布线的特点,提出一种新的无网格拆线重布算法.该算法显式地表示并动态更新线网所属区域的拥挤程度.在拆线重布进行待布线网的路径搜索时,每个扩展节点中增加拆除线网周边的拥挤权重,从而将待布线网的路径搜索过程和拆除线网的选择过程统一起来,有效地提高了被拆除线网重新布通的可能性.该算法利用改进的二叉区间树有效组织中间数据,降低计算的复杂度.实验结果表明,该算法能有效消除布线顺序对布线结果的影响,提高布通率,且算法运行速度较快.     

A heuristic for constructing a rectilinear Steiner tree by reusing routing resources over obstacles

The obstacle-avoiding rectilinear Steiner minimal tree (OARSMT) problem is a hot topic in very-large-scale integration physical design. In practice, most of the obstacles occupy the device layer and certain lower metal layers. Therefore, we can place wires on top of the obstacles. To maximize routing resources over obstacles, we propose a heuristic for constructing a rectilinear Steiner tree with slew constraints. Our algorithm adopts an extended rectilinear full Steiner tree grid as the routing graph. We mark two types of Steiner point candidates, which are used for constructing Steiner trees and refining solutions. A shortest path heuristic variant is designed for constructing Steiner trees and it takes into account slew constraint by inhibiting growth. Furthermore, we use a pre-computed strategy to avoid calculating slew rate repeatedly. Experimental results show that our algorithm maximizes routing resources over obstacles and saves routing resources outside obstacles. Compared with the conventional OARSMT algorithm, our algorithm reduces the wire length outside obstacles by as much as 18.74% and total wire length by as much as 6.03%. Our algorithm improves the latest related algorithm by approximately 2% in terms of wire length within a reasonable running time. Additionally, calculating the slew rate only accounts for approximately 15% of the total runing time.     

Maze Routing Steiner Trees With Delay Versus Wire Length Tradeoff

In this paper, we address the problem of generating good topologies of rectilinear Steiner trees using path search algorithms. Various techniques have been applied in order to achieve acceptable run times on a Maze Router that builds Steiner trees. A biasing technique proposed for wire length improvement, produces trees that are within 2% from optimal topologies in average. By introducing a sharing factor and a path-length factor we show how to trade-off wire length for delay. Experimental results show that our algorithm generates topologies with better delay compared to state of the art heuristics for Steiner trees, such as AHHK (from 26% to 40%) and P-Trees (from 1% to 30% and from 6% to 21% in the presence of blockages) while keeping the properties of a routing algorithm. An important motivation for this work lies in the fact that it can be used for estimation in the early stages as well as for actual routing, thereby improving the convergence and timing closure of the design significantly. We also provide some valuable theoretical background and insights on delay optimization and on how it relates to our maze router implementation.      

Load balance in hierarchical routing network

In this article, the problem of load balance in hierarchical routing network is studied. Since conventional shortest path first (SPF) algorithm over aggregated topology in hierarchical routing network may result in worse routing performance, a traffic sharing path selection algorithm and a variable weight scheme are put forward for hierarchical routing network, which can equilibrate the utilities of link resources and reduce the blocking probability of connections with the improvement on survivability. Simulations are conducted to evaluate proposed variable weight and traffics balance (VWTB) algorithm, which combines traffic sharing and variable weight. From the simulation results, it can be found that the proposed VWTB algorithm can balance the traffics and equilibrate the utilities of link resources significantly.     

A routing algorithm for FPGAs with time-multiplexed interconnects

Previous studies show that interconnects occupy a large portion of the timing budget and area in FPGAs.In this work,we propose a time-multiplexing technique on FPGA interconnects.In order to fully exploit this interconnect architecture,we propose a time-multiplexed routing algorithm that can actively identify qualified nets and schedule them to multiplexable wires.We validate the algorithm by using the router to implement 20 benchmark circuits to time-multiplexed FPGAs.We achieve a 38%smaller minimum channel width and 3.8%smaller circuit critical path delay compared with the state-of-the-art architecture router when a wire can be time-multiplexed six times in a cycle.     

一种用于光网络的高效业务疏导辅助图及动态业务疏导算法

利用辅助图,研究了光网络中的业务疏导技术。为解决传统的辅助图存在着模型复杂、波长通道的带宽利用率不高等问题,提出一种新的业务疏导辅助图,能够更有效地利用已有波长通道,避免低效的路由;为了降低动态业务疏导算法的复杂度,提出了一种简化的k最短路径算法,并以此为基础提出了多种疏导策略。仿真结果表明,本文提出的辅助图及其业务疏导算法,可以有效地减少阻塞率。     

A hop‐by‐hop delay‐constrained routing algorithm with explicit loop avoidance and backup routing information

QoS Routing is crucial for QoS provisioning in high‐speed networks. In general, QoS routing can be classified into two paradigms: source routing and hop‐by‐hop routing. In source routing, the entire path to the destination node of a communication request is locally computed at the source node based on the global state that it maintains, which does not scale well to large networks. In hop‐by‐hop routing, a path‐selecting process is shared among intermediate nodes between the source node and the destination node, which can largely improve the protocol scalability. In this paper, we present the design of hop‐by‐hop routing with backup route information such that each intermediate node can recursively update the best known feasible path, if possible, by collectively utilizing the routing information gathered thus far and the information that it locally stores. Such a route is kept as a backup route and its path cost is used as a reference to guide the subsequent routing process to search for a lower‐cost constrained path and avoid performance degradation. In this way, the information gathered is maximally utilized for improved performance. We prove the correctness of our presented algorithm and deduce its worst message complexity to be O(∣V∣²), where ∣V∣ is the number of network nodes. Simulation results indicate that, however, the designed algorithm requires much fewer messages on average. Therefore it scales well with respect to the network size. Moreover, simulation results demonstrate that the cost performance of our algorithm is near‐optimal. Copyright © 2004 John Wiley & Sons, Ltd.     

Novel disjoint path selection scheme based on link availability in ASON

Risk-disjoint routing is an efficient way to improve network survivability.In this article, a partial risk-disjoint routing algorithm based on link availability (PRDRA-LA) is proposed based on the complete risk-disjoint routing algorithm (CRDRA).While calculating the protection path with PRDRA-LA, the links that share risks with the links in the working path are filtered by link availability.In addition, the risk disjoint degree between the protection path and the working path can be adjusted freely.Simulation results showed that when compared with CRDRA, routing connections with PRDRA-LA can achieve improved survivability while the number of connections that can be successfully routed over the current network is kept from serious decline.     

An Ant-Based Approach for Dynamic RWA in Optical WDM Networks

In this paper, we propose a new ant-based algorithm for the dynamic routing and wavelength assignment (RWA) problem in optical WDM networks under the wavelength continuity constraint. Unlike conventional approaches, which usually require centralized global network information, our new RWA algorithm constructs the routing solution in a distributed manner by means of cooperative ants. To facilitate the ants’ foraging task, we adopt in our algorithm a probabilistic routing table structure for route selection. The new algorithm is highly adaptive in that it always keeps a suitable number of ants in the network to cooperatively explore the network states and continuously update the routing tables, so that the route for a connection request can be determined promptly by the current states of routing tables with only a small setup delay. Some new schemes for path scoring and path searching are also proposed to enhance the performance of our ant-based algorithm. Extensive simulation results upon three typical network topologies indicate that the proposed algorithm has a very good adaptability to traffic variations and it outperforms both the fixed routing algorithm and the promising fixed–alternate routing algorithm in terms of blocking probability. The ability to guarantee both a low blocking probability and a small setup delay makes the new ant-based routing algorithm very attractive for both the optical circuit switching networks and future optical burst switching networks     

功率控制下基于能耗最小的Ad hoc网络路由选择算法

在节点MAC层发射功率可控情况下，提出了一种基于路径能量消耗最小的路由路径选择算法。该算法根据链路的能量消耗情况来进行路由路径选择，达到节约网络能量的目的。仿真表明．该算法可以动态调整网络路由路径，从而使所选路径的能量消耗达到最小。