SDRAM存储器的交错机制及其应用

在分析sDRAM(同步动态随即存取存储器)存储器的结构和访问时序的基础上,介绍了SDRAM的交错机制,并分析了交错机制对SDRAM访问性能的影响.通过对基于页的交错和基于体的交错方式的对比分析,得出基于页的交错方式具有更好的访问性能的结论,并通过实际测试证明了这一结论.测试结果表明,在相同的硬件条件下,采用基于页的交错方式比基于体的交错方式提高4%～5%的性能.     

基于当代DRAM结构的存储器控制器设计

存储器带宽以及延迟与3D架构(体、行、列)特点的DRAM芯片的存取方式紧密相关.连续访问一行的不同列与连续访问一体的不同行其带宽存在数量级的差异.本文介绍一种存储器控制器设计,一项依靠重排序存储器存取访问的顺序来挖掘3D存储器架构局部性的技术.     

基于FPGA的三端口非透明型SDRAM控制器

本文采用Altera公司的Stratix系列FPGA实现了一个三端口非透明型SDRAM控制器,该控制器面向用户具有多个端口,通过轮换优先级的设计保证了多个端口平均分配SDRAM的带宽且不会降低传输速率。将访问SDRAM空间虚拟成一个简单的访问三口RAM的操作,采用乒乓的DMA传输机制大大提高了数据传输的带宽和效率。     

NetMagic平台上正则表达式匹配技术实现

在基于有限状态自动机的正则表达式匹配技术中,存储需求和匹配性能是一对相互制约的因素.统计分析发现,对于给定的自动机,状态的访问概率分布呈Zipf规律.为解决存储和性能的矛盾,设计并实现了基于Net Magic的两级存储的匹配引擎;根据状态的访问概率特性,将访问概率较高的状态配置在小容量的高速存储器中,访问概率较低的状态配置在大容量的低速存储器中,从而达到存储与性能的平衡.同时利用FPGA内部多RAM块特性,实例化多个匹配引擎,进一步使匹配速度线性提升.在资源充裕的条件下,理论上可达到65Gbps的吞吐量.实验表明单位存储代价大幅降低,但受限于Net Magic存储资源、频率及端口速率,实际性能为2.1Gbps.     

MPC8280集成的SDRAM存储控制器设计

介绍了NXP公司PowerQUICC II系列MPC8280处理器集成的SDRAM存储控制器的工作原理和工作模式，并在某国产化8280嵌入式系统开发板上，利用SDRAM存储控制器对4片SDRAM芯片进行读写操作。实际操作结果表明，该国产化8280处理器SDRAM存储控制器功能正常，可以访问SDRAM外设存储器。     

基于FPGA和DSP的高分辨率图像采集系统

介绍了一种高分辨率图像数据采集系统的实现方案.该方案采用了现场可编程门阵列(FPGA)数字信号处理器(DSP)的体系结构,利用FPGA实现图像数据检测、采集、缓冲、预处理,并协调系统各部分的工作,利用DSP对图像数据进行JPEG压缩,通过PC104总线将压缩后的数据上传至主机.该方案中,由FPGA控制的高速大容量同步动态随机存储器(SDRAM)作这图像数据的帧存,解决了高分辨率图像采集中容量和速度上的问题,SDRAM分时供FPGA和DSP访问的机制提高了数据存取的效率.JPEG压缩方法大大降低了数据传输所需的带宽并减少了存储所需的容量.该系统能够对高至2 048×1 536的多种分辨率的图像实现数据采集和压缩.     

面向图像转置和分块处理的一种高效内存访问策略

图像转置和图像分块处理在目前图像处理过程中是经常用到的两种操作.对于实时图像处理,图像转置和图像分块的效率直接影响到实时性,而图像转置和图像分块的效率和内存访问效率密切相关.而访存效率与计算机体系结构、存储器结构和实际操作策略有直接的关系.根据存储器的读写特性提出一种分段存储的高效内存访问策略,通过理论分析得出合理的分段长度,即图像转置时分段长度的选择与DDR2 SDRAM的型号有关;而图像分块时分段长度的选择则与数据块的大小有关.结合工程实际应用还推导了普适的总线地址与存储器物理地址之间的映射,同时给出了一种硬件实现方式,针对不同的应用,仅需要替换地址映射模块,具有一定的通用性和扩展性.分段存储方法已经在SAR实时成像压缩系统中得到有效的验证.     

基于文件分割的二进制大对象存取算法

海量媒体数据存储系统中,文件过大或多用户并发访问等原因会造成二进制大对象(BLOB)存储过程失效。为提高存储系统存取非结构二进制文件的可靠性和稳定性,提出并建立了BLOB存储可靠性概率模型,证明了使用数量较多的文件分块和较小的分块大小,可提高BLOB存储成功的概率。根据该模型,改进了关系数据库存储环境下的BLOB数据存取技术。通过建立基于文件分块的存储结构,提出了BLOB数据分块存储和重新装配新算法并进行了仿真实验。BLOB存取算法的仿真实验和实际应用表明,该存取算法有效降低了媒体数据存储失效的概率。     

FPGA实现高速实时多端口SDRAM控制器的研究

为了满足多个设备同时存取高速数据的需求,介绍了利用Xilinx高性能可编程逻辑器件Virtex6 FPGA实现高速实时多端口DDR3 SDRAM控制器的原理和方法,在一个实时图像处理系统平台上实现了对单片SO-DIMM DDR3内存条的多设备实时访问控制。通过ChipScope工具采样输入输出数据,验证其可行性,分析计算出端口速率和其他主要时间参数。实验结果显示高速实时多端口SDRAM控制器具有集成度高、传输带宽高、功耗低的优点。在多设备同时读写高速数据的系统中具有很高的实用价值。     

基于FPGA的一种存储器字节访问方法

计算机系统普遍采用较宽的存储器总线结构以提高吞吐率,这导致了以字节为基本单位读写数据的不便。通过对主流SDRAM存储器的访问机制的分析,为SDRAM存储控制器设计了一种数据自动对齐方案,该方案能够根据输入的字节地址和数据自动产生所需的存储器控制信号,并将数据对齐到正确的字节位置。详细阐述了生成地址、字节控制信号以及进行字节对齐的原理与方法,并在FPGA芯片上实现。与基于Cache以及基于两次存储器读写操作的方案相比较,新方案占用硬件资源更少,存储器带宽利用率更高。     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.     

Editorial: Special issue on recent advances in hybrid control theory and applications

正The demands of a rapidly advancing technology for faster and more accurate controllers have always had a strong influence on the progress of automatic control theory.In recent years control problems have been arising with increasing frequency in widely different areas,which cannot be addressed using conventional control techniques.The principal reason for this is the fact that a highly competitive economy is forcing systems to operate in regimes where     

Information for Authors

正Aim The Journals of Zhejiang University-SCIENCE(A/B/C)areedited by the international board of distinguished Chinese andforeign scientists,and are aimed to present the latest devel-opments and achievements in scientific research in China andoverseas to the world’s scientific circles,especially to stimulateand promote academic exchange between Chinese and for-eign scientists everywhere.     

Enhancing a leaf radiative transfer model to estimate concentrations and in vivo specific absorption coefficients of total carotenoids and chlorophylls a and b from single-needle reflectance and transmittance

The relative concentrations of different pigments within a leaf have significant physiological and spectral consequences. Photosynthesis, light use efficiency, mass and energy exchange, and stress response are dependent on relationships among an ensemble of pigments. This ensemble also determines the visible characteristics of a leaf, which can be measured remotely and used to quantify leaf biochemistry and structure. But current remote sensing approaches are limited in their ability to resolve individual pigments. This paper focuses on the incorporation of three pigments—chlorophyll a, chlorophyll b, and total carotenoids—into the LIBERTY leaf radiative transfer model to better understand relationships between leaf biochemical, biophysical, and spectral properties.Pinus ponderosa and Pinus jeffreyi needles were collected from three sites in the California Sierra Nevada. Hemispheric single-leaf visible reflectance and transmittance and concentrations of chlorophylls a and b and total carotenoids of fresh needles were measured. These data were input to the enhanced LIBERTY model to estimate optical and biochemical properties of pine needles. The enhanced model successfully estimated reflectance (RMSE = 0.0255, BIAS = 0.00477, RMS%E = 16.7%), had variable success estimating transmittance (RMSE = 0.0442, BIAS = 0.0294, RMS%E = 181%), and generated very good estimates of carotenoid concentrations (RMSE = 2.48 µg/cm², BIAS = 0.143 µg/cm², RMS%E = 20.4%), good estimates of chlorophyll a concentrations (RMSE = 10.7 µg/cm², BIAS = − 0.992 µg/cm², RMS%E = 21.1%), and fair estimates of chlorophyll b concentrations (RMSE = 7.49 µg/cm², BIAS = − 2.12 µg/cm², RMS%E = 43.7%). Overall root mean squared errors of reflectance, transmittance, and pigment concentration estimates were lower for the three-pigment model than for the single-pigment model. The algorithm to estimate three in vivo specific absorption coefficients is robust, although estimated values are distorted by inconsistencies in model biophysics. The capacity to invert the model from single-leaf reflectance and transmittance was added to the model so it could be coupled with vegetation canopy models to estimate canopy biochemistry from remotely sensed data.     

Mr. Twinn’s bombes

This article discusses the history and design of the special versions of the bombe key-finding machines used by Britain’s Government Code & Cypher School (GC&CS) during World War II to attack the Enigma traffic of the Abwehr (the German military intelligence service). These special bombes were based on the design of their more numerous counterparts used against the traffic of the German armed services, but differed from them in important ways that highlight the adaptability of the British bombe design, and the power and flexibility of the diagonal board. Also discussed are the changes in the Abwehr indicating system that drove the development of these machines, the ingenious ways in which they were used, and some related developments involving the bombes used by the U.S. Navy’s cryptanalytic unit (OP-20-G).