电子与通信工程专业英语Unit 16Embedded Systems and Applicatio-修改

1、1 1电子与通信工程电子与通信工程专业英语专业英语Unit 16 Unit 16 Embedded Embedded Systems and Systems and ApplicatioApplicatio2 21What are embedded systems?A completely new branch of computer engineering is that of embedded systems. It is the development of specialized computer equipment that is not programmable by the us

2、er, but is dedicated to drive or control a piece of equipment, such as medical equipment or machinery. The skill of embedded systems is marrying the computer technology with the mechanical engineering design 1.3 34 45 56 67 78 89 9 You dont need to load programs or data from a slow disk drivemost in

3、formation needed will be in fast ROM.Embedded systems can be roughly defined as “a system that is not primarily a computer but contains a processor”. But rather than focusing on a definition, it is useful to consider aspects that most embedded systems share, at least to some degree.(1) Embedded syst

4、ems are frequently price and size sensitive.Many embedded systems such as PDAs or cell-phones are high-volume, 10 10low-cost and low-margin. This requires use of the cheapest components possible, which typically means simple processors and small memory (RAM and NVRAM/Flash)3. This causes embedded sy

5、stems software to trade off maintainability aspects such as portability, clarity, or modularity for performance optimization aspects such as a small boot image footprint, a small RAM footprint, and small cycle requirements. The increased up-front software development costs and periodic maintenance c

6、osts are amortized by the high-volume sales, and outweighed by the continuous hardware cost savings of cheaper components4.11 11Many other embedded systems, though not so price-sensitive, have physical constraints on form factor or weight to use the smallest components possible. Again, this favors p

7、erformance optimization at the cost of maintainability.In addition to trading off portability, clarity, or modularity, embedded systems may also require optimization by using a low-level language, e.g. assembly rather than C, or C rather than code automatically generated from a UML model5. However,

8、this hand tuning is typically only applied to small portions of the software identified by the 10% guideline as being the major performance bottlenecks.12 12(2) Embedded systems often have power limitations.Many embedded systems run from a battery, either continually or during emergencies. Therefore

9、, power consumption performance is favored in many embedded systems at the cost of complexity and maintainability.(3) Embedded systems are frequently real-time.By nature, most embedded systems are built to react in real-time to data flowing to and through the system. The real-time constraints again

10、favor performance aspects (particularly cycles usage) over maintainability aspects. 13 13There are generally both hard real-time constraints, which require an event to be handled by a fixed time, and soft real-time constraints, which set limits on the average event response time. Real-time operating

11、 systems use preemptive prioritized scheduling to help ensure that real-time deadlines are met, but careful thought is required to divide processing into execution contexts (threads), set the relative priorities of the execution contexts, and manage control/data flow between the contexts.14 14(4) Em

12、bedded systems frequently use custom hardware.Embedded systems are frequently comprised of off-the-shelf processors combined with off-the-shelf peripherals6. Even though the components may be standard, the custom mixing and matching requires a high degree of cohesion between the hardware and the sof

13、twarea significant portion of the software for an embedded system is operating system and device driver software. Though this low-level software is often available for purchase, license, or free use, 15 15frequently a large portion of the operating system for an embedded system is custom-developed i

14、n-house, either to precisely match the hardware system at hand, or to glue together off-the-shelf software in a custom configuration.Often the functionality of an embedded system is distributed between multiple peer processors and/or a hierarchy of master/slave processors. Careful thought is require

15、d regarding the distribution of processing tasks across processors, and the extent, method, and timing of communication between processors.16 16Furthermore, many embedded systems make use of specialized FPGAs or ASICs, and thus require low-level software to interact with the custom hardware.(5) Embe

16、dded systems are predominantly hidden from viewBy nature, embedded systems typically have a limited interface with their “user”(real user or another component of the super-system). Thus, much of the system is developed to meet the software functional specifications developed during architecture and

17、high-level design, rather than the user requirements.17 17(6) Embedded systems frequently have monolithic functionality.Most embedded systems are built for a single primary purpose. They can be decomposed into components, and potentially the components could have low cross-cohesion and cross-couplin

18、g. That is, each component could serve a distinct purpose, and the interactions between components could be restricted to a few well-defined points. Nevertheless, the system as a whole will not function unless most or all of the components are operational. 18 18A system that requires all components

19、to function before the system as a whole achieves useful functionality is a “monolithic system”. This non-linear jump in system functionality as a function of component functionality is in contrast to some other types of software, where the system may be 50% functional (or more) when the software is

20、 50% complete.19 19For example, a space probe is built to travel by or to other planets and send back information about them. Though there are many lower-level responsibilities of the space probe components, such as targeting, landing, deploying sensors, deploying solar panels, and communications. E

21、ach of these lower-level responsibilities is an indispensable component of the overarching functionality. The space probe will fail if any of these vital components is missing, even if all other components are completely functional.2020Another example is a cell phone, in which all the sub-features s

22、uch as the user interface, the cellular base station selection, the vocoder, and the communications protocols are all vital aspects of the over-arching goal to transfer bi-directional audio information between the user and specific remote nodes.These are in contrast to other software regimes, such a

23、s web services or desktop tools, in which lower-level responsibilities are more likely to contribute independently to the aggregate system functionality rather than serving as indispensable parts of a monolithic whole.21 21Though the software components of an embedded system are combined into a mono

24、lithic functionality, the components themselves are often very distinct. Embedded systems will frequently combine software components that perform signal processing, low-level device driver I/O, communications protocols, guidance and control, and user interfaces. Each of these specialized components

25、 requires a distinct developer skill set.2222(7) Embedded systems frequently have limited development tools.Though some software regimes have a whole host of tools to assist with software development, embedded systems software development are more limited, and frequently use only basic compiler tool

26、s. This is in part because embedded systems often use custom hardware, which may not have tool support, and because embedded systems are often real-time and performance constrained, 2323making it difficult to freeze the entire execution context under the control of a debugger or transfer control and

27、 data between the embedded target and a host-based tool, or capture extensive execution-tracing logs.Because of the limited choices of commercial tools for embedded systems software development, many embedded system projects create their own tools to use for debugging and testing, or at least augmen

28、t commercial tools with in-house tools.2424(8) Embedded systems frequently have stringent robustness requirements.Embedded systems are often used in harsh environments and for mission-critical or medical purposes. Therefore, requirements for reliability, correct exception handling, and mean time bet

29、ween failures are typically more stringent for embedded systems than for many other types of software. This translates into rigorous development processes and testing requirements. In turn, this increases the overhead needed to make a release of software.2525Some types of embedded systems are subjec

30、t to regulatory requirements that purport to reduce fault rates by mandating the software development process, or at least specifying what documentation must accompany the embedded systems product.Furthermore, for several types of embedded systems, it is difficult or even impossible to upgrade firmw

31、are, which emphasizes the need to “get it right” in the systems initial commercial release.2626NEW WORDS AND PHRASESembedded system 嵌入式系统microwaven.微波炉micro-controller n.微(型)控制器consolen.控制台a matter of course理所当然的事，必然的结果in tandem with同串联，同合作roughlyadv.概略地，粗糙地2727form factor外形因素real-time adj.实时的off-th

32、e-shelf从商店可以直接购买的，非顾客定制的PDA个人数字助理trade off交替换位，交替使用，卖掉portabilityn.可携带，轻便clarityn.清楚，透明modularity n.计模块性up-front adv.在前面，在最前面2828amortize vt.,vi. 分期清偿 peripheraladj.外围的 stringent严厉的，迫切的harshadj.粗糙的，荒芜的，苛刻的robustnessn. 健壮性preemptiveadj.有先买权的，有强制收购权的，抢先的execution context计执行文本2929FPGAabbr.可编程器件ASICabbr

33、.电特定用途集成电路predominantlyadv.支配性地，主要地，有影响地monolithic n.单片电路，单块集成电路architecturen.建筑，建筑学，体系机构cohesion n.结合，凝聚3030cross-coupling交叉耦合non-linear adj.非线性的solar panels太阳电池板vitaladj.生死攸关的，重大的，生命的，生机的compiler n.编辑者，计编译器rigorous adj.严格的，严厉的，严酷的，严峻的be subject to受支配paramountadj.极为重要的compromisen., vt., vi. 妥协，折中st

34、ands to reason显而易见31 31NOTES1 The skill of embedded systems is marrying the computer technology with the mechanical engineering design.句中“marry with ”应译为“与结合/混合”。本句可译为：嵌入式系统与计算机工程技术相结合，非常适用于机械工程设计。32322 It stands to reason that there are companies that specialize in the development of embedded syste

35、ms, either independently, or in tandem with the machinery with which theyre to be used. More and more, engineering firms are calling on this kind of expertise to upgrade their products in every way imaginable. “stands to reason”意为“显而易见的”、“顺理成章的”，“engineering firms”意为“工程公司”。3333本句可译为：这就是为什么有的公司擅长于嵌入式

36、系统开发的原因，独立地或者联合开发机器设备。在你能想到的任何方面，越来越多的技术公司召集这类专家去升级他们的产品。3 This requires use of the cheapest components possible, which typically means simple processors and small memory (RAM and NVRAM/Flash). RAM即Random-access Memory，意为“随机存取存储器”；NVRAM即NonVolatile Random Access Memory，意为“非易失随机存储器”；Flash也是一种非易失随机存储器

37、，我们通常称它为闪速存储器。34344 The increased up-front software development costs and periodic maintenance costs are amortized by the high-volume sales, and outweighed by the continuous hardware cost savings of cheaper components.“high-volume sales”意为“高调销售”，指在销售过程中的广告、推广宣传。5 In addition to trading off portabili

38、ty, clarity, or modularity, embedded systems may also require optimization by using a low-level language, e.g. assembly rather than C, or C rather than code automatically generated from a UML model. “low-level language”指用于计算机编程的低级语言，如汇编语言。3535本句可译为：除了要折中考虑可移植性、透明性或模块化外，嵌入式系统还需要使用低级语言进行优化。例如，汇编优于C语言，

39、C语言又优于统一建模语言中自动生成的代码。6 Embedded systems are frequently comprised of off-the-shelf processors combined with off-the-shelf peripherals. 句中“off-the-shelf”意为“现货供应，在存货商品中能得到的；非定制的”，这里可译为“通用的”。本句可译为：嵌入式系统通常由通用处理器和通用外围设备结合组成。3636EXERCISES. Translate the following phrases into English.嵌入式系统 特定用途集成电路 数字助理 交替

40、使用 通信协议 微控制器 微波炉 实时系统3737. Translate the following paragraph into Chinese.By nature, most embedded systems are built to react in real-time to data flowing to and through the system. The real-time constraints again favor performance aspects (particularly cycles usage) over maintainability aspects. Th

41、ere are generally both hard real-time constraints, which require an event to be handled by a fixed time, and soft real-time constraints, which set limits on the average event response time. Real-time operating systems use preemptive prioritized scheduling to help ensure that real-time deadlines are

42、met, 3838but careful thought is required to divide processing into execution contexts (threads), set the relative priorities of the execution contexts, and manage control/data flow between the contexts.3939参考译文第十六单元 嵌入式系统及其应用1什么是嵌入式系统？嵌入式系统是计算机工程领域的一个全新分支。该系统用于开发专用计算机设备，这种专用计算机设备不是为用户编程使用的，而是用于驱动或控制

43、一台设备，如医疗设备或机器。嵌入式系统与计算机工程技术相结合，非常适用于机械工程设计。4040嵌入式系统是一种嵌入到设备内的专用计算机。例如，微波炉就包含有嵌入式系统，通过它来响应操作面板的输入、控制LCD显示、控制加热元件的开或关来烹调食物。嵌入式系统通常采用微控制器，微控制器虽然只是一个元件，但它包含了计算机所具有的许多功能。摩托罗拉和英特尔公司研发了一些最通用的微控制器。当工程师们想到其他工程项目都可以从嵌入式系统技术中受益时，嵌入式系统市场就开始迅猛增长。现在，几乎任何设备中都有嵌入式系统，从食物料理机到汽车，甚至更大型的设备。生活在计算机时代意味着所有的机械设备十有八九将被植入嵌入式

44、系统。41 41嵌入式系统可分为不同的级别。电脑玩具和厨房设备是嵌入式系统最简单的形式。大多数复杂医疗设备实际上都有不止一个的嵌入式系统在其中。虽然上述事实表明我们使用的机器(更不用说我们日常生活中使用的)非常有效率，还表明维修嵌入式机器的过程将变得更困难、更昂贵，但是这还意味着我们的时间被嵌入式系统机器解放了，我们有了更多的时间来做我们想做的事了。例如，我们都使用有嵌入式系统的洗衣机。我们买的汽车里也越来越多地安装了嵌入式系统。甚至用于制造的工具也得益于嵌入式系统。这就是为什么有的公司擅长于嵌入式系统开发的原因，他们独立地或者联合开发机器设备。在你能想到的任何方面，越来越多的技术公司召集这类

45、专家去升级他们的产品。42422如果没有嵌入式系统当你坐进车里，插入车钥匙打开开关，(然后)从你的手袋里取出一张3.5寸软盘，把它插入仪表板上的插槽中，接着你在方向盘上用手指敲击，直到操作系统提示符出现在仪表板的LCD显示器上。通过中心操作台的光标键，你选择了电子点火程序，然后转动钥匙发动引擎。在上班的路上，你想听音乐，于是你将程序光盘插入到播放器中，等待绿灯闪烁后才表明播放器中的数字信号处理器准备完毕，然后才能插入你的音乐CD。43433如果有嵌入式系统 你不需要通过传统的用户界面去设定哪个程序才是需要运行的，汽车的电子点火程序将自动对车钥匙做出响应。 你不需要向你的设备加载程序你所需要的程

46、序都已经加载了(虽然一些新型智能手机可以下载扩展软件)。 你不需要浪费时间去等待操作系统加载如果需要操作系统的话，也没有其他导致它加载缓慢的负担。 你不需要从低速磁盘驱动加载程序或数据几乎全部需要的信息都固化在了高速ROM中。4444嵌入式系统的广义定义为“一个包含有处理器的但又不通用的计算机”。我们还应该深入研究它的定义，这有助于我们理解大多数嵌入式系统共有的特性。(1) 嵌入式系统通常在成本和尺寸方面要求较高。许多如掌上电脑或移动电话这类嵌入式系统都具有高调销售、价格便宜和利润率低的特点。这就要求尽可能使用最便宜的器件，即使用简单的处理器和体积小的存储器(RAM和NVRAM/Flash)。

47、这就要求嵌入式系统软件在易维护特性上折中考虑，如可移植性、透明性；4545或具备可性能优化的模块化特性，如小的启动引导镜像封装、小的RAM封装和小的循环周期。这将增加前期的软件开发成本和分摊在因高调销售中的周期维护费用，这些费用都超过了在硬件中因选用便宜器件节省下来的成本。另一些嵌入式系统，虽然成本压力不大，但却在形状或重量上有限制，需选用小体积的器件。并且，这种受人欢迎的性能优化是以牺牲可维护性为代价的。4646除了要折中考虑可移植性、透明性或模块化外，嵌入式系统还需要使用低级语言进行优化。例如，汇编优于C语言，C语言又优于统一建模语言中自动生成的代码。然而，这种手工调整通常只在软件中的小部

48、分有应用，仅占10%，这就是软件性能的首要瓶颈所在。(2) 嵌入式系统通常有功率限制。大多数嵌入式系统靠电池供电工作，有的需持续工作，有的则在紧急情况下工作。因此，电力损耗特性是许多以复杂性和可维护性为代价的嵌入式系统必须考虑的问题。4747(3) 嵌入式系统通常是实时的。嵌入式系统设计的初衷，就是用来对流出和流入系统实时数据进行响应。实时约束再次对可维护性提出了更高的性能要求。通常有硬实时约束和软实时约束两种形式，硬实时要求事件必须在要求的时间内被响应，软实时设定了事件的平均响应时间范围。实时操作系统采用强制优先调度的方法帮助确定实时期限时间是否到达，但要仔细考虑划分进程为多个执行文本(线程

49、)、设置线程的相对优先级和管理文本间的控制或数据流。4848(4) 嵌入式系统通常使用用户硬件。嵌入式系统通常由通用处理器和通用外围设备结合组成。即使器件是标准的，但是自定义的混合和匹配要求硬件和软件高度融合嵌入式系统最重要的软件是操作系统和设备驱动软件。虽然这种低级代码软件通常可以通过购买、授权使用或免费使用的方式获得，但嵌入式系统使用的操作系统中的大部分通常都是由用户自定义开发的，不管是为了匹配已有的硬件系统，或是将通用的成品软件融入到用户配置中。4949嵌入式系统的功能通常采用分布式结构实现，一般分布到多层的处理器和(或)多级的主/从处理器中。需要仔细考虑处理器间的这种进程任务的分布，还

50、有范围、方式和处理器间的同步通信。此外，许多嵌入式系统使用专用FPGA和ASIC实现，因而需要通过低级语言程序与用户硬件实现结合。(5) 嵌入式系统最大的特点是嵌入设备。出于设计的考虑，嵌入式系统一般与它们的“用户”(真实用户或其他超级系统的部件)只有有限的接口。因此，许多系统在设计时都必须满足该软件功能标准，这些标准只在结构和顶层设计时使用，一般用户不必考虑。5050(6) 嵌入式系统通常具有单片电路功能。多数嵌入式系统是为独立初级的应用设计的。它们可以被融入到元件中，潜在地与元件间存在着交叉结合和交叉耦合。即每个元件可能适用于不同的用途，元件间的相互联系可能只限于少数几个定义明确的点。不过

51、，作为整体的系统直到大多数或全部元件都工作后才会运行。这种在整体系统运行前需要所有元件全部预先运行好，并以此来获得实用的功能的系统称为“单片系统”。这个系统功能中的非线性跳转作为元件功能的函数，与其他类型软件形成了鲜明对比，其他系统在软件运行50%的情况下可能实现50%(或更多)功能。51 51例如，一个航天探测器绕地球飞行或飞往其他行星，并回传探测到的信息。尽管航天探测器要完成很多低级别的任务，如定标、着陆、展开传感器、展开太阳能电池板和通信，但每一个这种低级别任务都是整体功能不可或缺的部件。即使其他所有重要部件都完成了相应功能，但只要有一个部件故障，就会导致航天探测器故障。另一个例子是手机

52、，它的所有子功能如用户界面、蜂窝基站选址、声码器和通信协议都是实现总体功能的重要组成因素。要实现的总体功能是：在用户和特定远端节点间传输双向语音信息。5252嵌入式系统与其他软件形式形成鲜明对照，如网页服务或桌面工具，它们的低级别功能更像是独立地为实现总体系统功能做出贡献，而不是整个单片系统不可获取的部分。虽然嵌入式系统的软件部件与单片电路功能融为一体，但部件本身通常是专门定制的。嵌入式系统常常将这些软件部件组合在一起完成信号处理、低等级设备驱动器输入/输出、通信协议、引导和控制以及用户界面等任务。每一个专门的部件都需要特定的开发工具集。5353(7) 嵌入式系统通常有限定的开发工具。虽然一些

53、软件方式具有大量协助软件开发的工具，但是嵌入式软件的开发却有诸多限制，并常常只使用基本编程器工具。部分原因是嵌入式系统常使用可能没有支持工具的用户硬件，另一个原因是嵌入式系统常常受实时和性能的约束，使它很难在调试器的控制下固化所有执行代码，或在嵌入式目标板与基于主机的工具间传输控制和数据信息，或捕获大量的指令跟踪记录。由于嵌入式系统软件开发的商业工具选择上存在诸多限制，许多嵌入式系统项目研制了自己的工具，用于调试和测试，或者至少对商用软件进行内部扩展。5454(8) 嵌入式系统常常有严格的鲁棒性要求。嵌入式系统常用于苛刻的环境和关键任务或医疗目的。因此，嵌入式系统对可靠性、异常纠错处理和故障平

54、均时间的要求比其他类型软件都要严格。这就要求开发和测试过程必须严格，也会增加软件发布的成本。一些类型的嵌入式系统受控制要求的支配，主要是为了通过托管软件开发过程来降低故障率，或至少指定嵌入式产品应该符合的文档格式。此外，对于几类嵌入式系统，很难或几乎不可能升级它们的固件，这里需强调的是需要“正常恢复”系统中的原始商业版本。5555EXTENSIVE TEXTEmbedded OSEmbedded operating systems have some features that distinguish them from real-time and general-purpose operat

55、ing systems. But the definition of an “embedded operating system” is probably even more ambiguous than that of an RTOS, and they come in a zillion different forms. But youll recognize one when you see one, although the boundary between general-purpose operating systems and embedded operating systems

56、 is not sharp, and is even becoming more blurred all the time.5656Embedded systems are being installed in tremendous quantities (an order of magnitude more than desktop PCs!): they control lots of functions in modern cars; they show up in household appliances and toys; they control vital medical ins

57、trumentation; they make remote controls and GPS (Global Position Systems) work; they make your portable phones work, etc.The simplest classification between different kinds of embedded operating systems is as follows:5757(1) High-end embedded systems. These systems are often downsized derivatives of

58、 an existing general purpose OS, but with much of the “ballast” removed. Linux has given rise to a large set of such derivatives, because of its highly modular structure and the availability of source code. Examples are: routers, switches, personal digital assistants, set top boxes.(2) Deeply embedd

59、ed OS. These OSes must be really very small, and need only a handful of basic functions. Therefore, 5858they are mostly designed from the ground up for a particular application. Two typical functions deeply embedded systems (used to) lack are high-performance graphical user interfacing or network co

60、mmunication. Examples are: automotive controls, digital cameras, portable phones. But also these systems get more graphics and networking capabilities The most important features that make an OS into an embedded OS are:5959(1) Small footprint. Designers are continuously trying to put more computing