科技英语5数字信号处理器原文与翻译.doc

Words and Expressionsfollow v. 遵循 memory n. 存储器register n. 寄存器 access v. 访问overlap v. 重叠 pipelining n. 流水线操作multiplier n. 乘法器 accumulator n. 累加器shifter n. 移位器 reference n. 寻址mantissa n. 尾数 exponent n. 指数cycle n. 机器周期 customize v. 定制，用户化package v. 封装 6digital signal processor 数字信号处理器von Neumann architecture 冯诺伊曼结构shared single memory 单一共享存储器program instruction 程序指令harvard architecture 哈佛结构fetch from 从获取circular buffer 循环缓冲区，环形缓冲区address generator 地址产生器fixed point 定点floating point 浮点binary point 二进制小数点available precision 可用精度dynamic range 动态范围scale range 量程smallest Resolvable Difference 最小分辨率scientific notation 科学计数法assembly language 汇编语言multi-function instructions 多功能指令parallel architecture 并行结构looping scheme 循环机制sampling frequency 采样频率on-chip memory 片内存储器well-matched 非常匹配software tools 软件开发工具low level programming language 低级编程语言high level programming language 高级编程语言third party software 第三方软件board level product 板级产品data register 数据寄存器ALU=Arithmetic Logical Unit 运算逻辑单元program sequencer 程序定序器peripheral sections 外设single integrated circuit 单片集成电路cellular telephone 蜂窝电话 printed circuit board 印刷电路板licensing agreement 专利使用权转让协定custom devices 定制器件extra memory 附加存储器stand alone 单机third party developer 第三方开发商multimedia operations 多媒体操作merged into 融合calculation-intensive algorithm 运算密集型算法Unit 5 Digital Signal ProcessorsDigital signal processing tasks can be performed by all processors. Specialized digital signal processors (DSPs), however, perform these tasks most efficiently and most quickly. While traditional processors follow the Von Neumann architecture model, which assumes a shared single memory to be used for both program instructions and data, DSPs use the Harvard or modified Harvard architecture , which includes multiple program and data memories, along with multiple buses to access them. This arrangement means that much less waiting is required when instructions or numbers are fetched from memory. In fact at least one of each can be fetched simultaneously. Such overlapping of tasks is called pipelining. In addition to multiple memories and buses, all DSPs have fast multipliers, accumulators, and shifters, and many have hardware support for circular buffers. Address generators can speed up accesses to memory locations referenced by registers. DSPs are available in two major classes: fixed point and floating point. The fixed point class represents real numbers in a fixed number of bits. The position of the binary point (similar to the decimal point) can be controlled by the programmer, and determines the range of numbers that can be represented. As the range increases, though, the available precision goes down, since fewer bits lie to the right of the binary point. In 16 bits, the formats 16.0, 15.1, 14.2, 13.3, 12.4, 11.5, 10.6, 9.7, 8.8, 7.9, 6.10, 5.11, 4.12, 3.13, 2.14, and 1.15 are possible. The dynamic range, calculated as 20log (Full Scale Range/Smallest Resolvable Difference), remains the same for all 16-bit formats, 20log= 96.3 dB.Figure 6.3 Van Neumann architectureFigure 6.4 Harvard architectureFloating point DSPs represent real numbers using a mantissa and an exponent, similar to scientific notation: Many combine mantissa and exponent into a 32-bit number. The dynamic range for floating point devices is calculated from the largest and smallest multipliers, where E is the exponent. Thus, for a representation that uses 24 bits for the mantissa and 8 bits for the signed exponent, the dynamic range is 20 log () = 1535.3 dB. A large dynamic range means the system has great power to represent a wide range of input signals, from very small to very large.Assembly language is the command language for DSPs. DSPs often have specialized instructions that make programming for common DSP tasks more convenient and more efficient. For example, most DSPs offer multi-function instructions that exploit their parallel architecture. Other constructs that are frequently offered are efficient looping schemes, since so many DSP operations involve a great deal of repetition.Choosing a DSP for a particular application is not always easy. The first decision is on whether to choose a fixed point or a floating point device. Generally, fixed point devices are cheaper and quicker, but floating point devices are more convenient to program and more suited to calculation-intensive algorithms. Second, the data width of the DSP determines how accurately it can represent numbers. Speed is another issue, not only how many cycles occur in each second, but also how many instructions execute in each cycle and how much work each of these instructions accomplishes. One way to assess the minimum requirements for the DSP is to estimate how many instructions must be executed for each received sample. When this number is multiplied by the sampling frequency, the minimum required number of instructions per second is obtained.The specific hardware and software features offered by a particular DSP can make one choice better than another, as can the amount of on-chip memory available. Sometimes DSPs are chosen because well-matched supporting hardware, particularly A/D and D/A converters, is obtainable. Frequently, the quality and convenience of the software tools, for both low level and high level programming languages, are also major factors, as is the availability of third party software. As always, cost is a factor. In fact, quite often, the DSP that is fastest and offers the most features, but also fits the budget, is the one selected.DSPs can be purchased in three forms, as a core, as a processor, and as a board level product. In DSP, the term core refers to the section of the processor where the key tasks are carried out, including the data registers, multiplier, ALU, address generator, and program sequencer. A complete processor requires combining the core with memory and interfaces to the outside world. While the core and these peripheral sections are designed separately, they will be fabricated on the same piece of silicon, making the processor a single integrated circuit.Suppose you build cellular telephones and want to include a DSP in the design. You will probably want to purchase the DSP as a processor, that is, an integrated circuit that contains the core, memory and other internal features. To incorporate this IC in your product, you have to design a printed circuit board where it will be soldered in next to your other electronics. This is the most common way that DSPs are used.Now, suppose the company you work for manufactures its own integrated circuits. In this case, you might not want the entire processor, just the design of the core. After completing the appropriate licensing agreement, you can start making chips that are highly customized to your particular application. This gives you the flexibility of selecting how much memory is included, how the chip receives and transmits data, how it is packaged, and so on. Custom devices of this type are an increasingly important segment of the DSP marketplace. There are several dozen companies that will sell you DSPs already mounted on a printed circuit board. These have such features as extra memory, A/D and D/A converters, EPROM sockets, multiple processors on the same board, and so on. While some of these boards are intended to be used as stand alone computers, most are configured to be plugged into a host, such as a personal computer. Companies that make these types of boards are called Third Party Developers. The best way to find them is to ask the manufacturer of the DSP you want to use. Look at the DSP manufacturers website; if you dont find a list there, send them an e-mail. They will be more than happy to tell you who are using their products and how to contact them.Keep in mind that the distinction between DSPs and other microprocessors is not always a clear line. For instance, look at how Intel describes the MMX technology addition to its Pentium processor: Intel engineers have added 57 powerful new instructions specifically designed to manipulate and process video, audio and graphical data efficiently. These instructions are oriented to the highly parallel, repetitive sequences often found in multimedia operations. In the future, we will undoubtedly see more DSP-like functions merged into traditional microprocessors and microcontrollers. The Internet and other multimedia applications are a strong driving force for these changes. These applications are expanding so rapidly, in twenty years it is very possible that the Digital Signal Processor may be the traditional microprocessor.Notes1. “冯诺伊曼结构”取名字美国杰出的数学家约翰冯诺伊曼（John Von Neumann,19031957）。他引导了20世纪初许多重大数学发现。他的主要成就包括：提出了存储程序计算机（stored program computer）的概念、对量子力学的数学公式化及在原子弹方面的工作。2 “哈佛结构”取名自20世纪40年代 Howard Aiken (19001973)领导的在哈佛大学（Harvard University）做的研究工作。3 本句可译为：首先要决定的是选择定点器件还是浮点器件。4. 本句可译为：和片内可用存储器大小能做出更佳选择的判断一样，特定数字信号处理器所提供的软硬件特点会使一个选择优于另一个选择。数字信号处理器 所有处理器都可以完成数字信号处理的任务。然而，专用数字信号处理器完成数字信号任务的效率和速度都是最好的。传统的处理器遵循冯诺伊曼模型，该模型采用一个单一的共享存储器，同时存储程序指令和数据；而数字信号处理器使用的是哈佛结构或改进哈佛结构，该结构包含多个程序和数据存储器以及访问这些存储器的多套总线。这样安排就意味着从存储器取指令或取数据所需的等待时间要少得多。实际上，至少可以同时取得一条指令和一个数据。这种任务的重叠称做流水线。除了多存储器和多总线之外，所有数字信号处理器都有快速的乘法器、累加器和移位器，而且许多数字信号处理器都有支持循环缓冲区的硬件。地址产生器可以加速对寄存器寻址的存储器访问。 数字信号处理器分为定点和浮点两大类。定点数字信号处理器使用固定的比特数来代表实数。二进制小数点的位置可以由编程人员决定，这个位置决定了可以表示的实数范围。可用精度要随着表示范围的增加而下降，因而二进制小数点右边的比特数减少了。在16位数据中，可能出现的格式有16.0，15.1，14.2，13.3，12.4，11.5，10.6，9.7，8.8，7.9，6.10，5.11，4.12，3.13，2.14和1.15。所有16位定点数据格式的动态范围都是一样的，都是。动态范围的计算方法为：（满量程范围/最小可分辨差别）。 浮点数字信号处理器使用尾数和指数来表示实数，这种方法和科学计数法很相似将尾数和指数组合成一个32位数。浮点器件的动态范围是用的最大值和最小值进行计算的，此处E是指数。这样，对于24位尾数和8位有符号指数的表示方法而言，动态范围是。大的动态范围意味着系统具备更大的、表示很宽范围输入信号的能力，从很小的信号到很大的信号。 汇编语言是数字信号处理器使用的命令语言。为了使常见数字信号处理任务的编程更加方便、高效，数字信号处理器往往采用专门指令。例如，多数数字信号处理器都提供多功能指令，这些指令利用数字信号处理器的并行结构。数字信号处理器往往还提供高效的循环结构，因为许多数字信号处理器运算都包含大量的重复性操作. 为特定应用选择合适的数字信号处理器不是很容易的。首先要明确的是选择定点器件还是浮点器件。一般而言，定点器件比较便宜，而且速度也较快；而浮点器件更便于编程，更适合于运算密集型的算法。第二，数字信号处理器的数据宽度决定了它所代表数据的精度。速度也是一个问题，速度不仅仅是指一秒内有多少个机器周期，而且还包含每个周期能够执行多少条指令以及这些指令中的每一条能够完成多少工作。一种评估数字信号处理器最低要求的办法是：估计对每个到来的样本必须执行多少条指令。这个数乘以采样频率就得到了所需每秒指令数的最小值。 某个特定数字信号处理器提供的某些特定的软、硬件特点能够让一种选择优于另一种选择，可用片内存储器数量同样也能做到这一点。有的时候，选