外文翻译--嵌入式系统与RTOS.docx

外文资料翻译embedded systems and rtosone of the more surprising developments of the last few decades has been the ascendance of computers to a position of prevalence in human affairs. today there are more computers in our homes and offices than there are people who live and work in them. yet many of these computers are not recognized as such by their users. in this chapter, well explain what embedded systems are and where they are found. we will also introduce the subject of embedded programming and discuss what makes it a unique form of software programming. well explain why we have selected c as the language for this book and describe the hardware used in the examples.1. what is an embedded system?an embedded system is a combination of computer hardware and softwareand perhaps additional parts, either mechanical or electronicdesigned to perform a dedicated function. a good example is the microwave oven. almost every household has one, and tens of millions of them are used every day, but very few people realize that a computer processor and software are involved in the preparation of their lunch or dinner.the design of an embedded system to perform a dedicated function is in direct contrast to that of the personal computer. it too is comprised of computer hardware and software and mechanical components (disk drives, for example). however, a personal computer is not designed to perform a specific function. rather, it is able to do many different things. many people use the term general-purpose computer to make this distinction clear. as shipped, a general-purpose computer is a blank slate; the manufacturer does not know what the customer will do with it. one customer may use it for a network file server, another may use it exclusively for playing games, and a third may use it to write the next great american novel.frequently, an embedded system is a component within some larger system. for example, modern cars and trucks contain many embedded systems. one embedded system controls the antilock brakes, another monitors and controls the vehicles emissions, and a third displays information on the dashboard. some luxury car manufacturers have even touted the number of processors (often more than 60, including one in each headlight) in advertisements. in most cases, automotive embedded systems are connected by a communications network.it is important to point out that a general-purpose computer interfaces to numerous embedded systems. for example, a typical computer has a keyboard and mouse, each of which is an embedded system. these peripherals each contain a processor and software and is designed to perform a specific function. another example is a modem, which is designed to send and receive digital data over an analog telephone line; thats all it does. and the specific function of other peripherals can each be summarized in a single sentence as well.the existence of the processor and software in an embedded system may be unnoticed by a user of the device. such is the case for a microwave oven, mp3 player, or alarm clock. in some cases, it would even be possible to build a functionally equivalent device that does not contain the processor and software. this could be done by replacing the processor-software combination with a custom integrated circuit (ic) that performs the same functions in hardware. however, the processor and software combination typically offers more flexibility than a hardwired design. it is generally much easier, cheaper, and less power intensive to use a processor and software in an embedded system.2. history and futuregiven the definition of embedded systems presented earlier in this chapter, the first such systems could not possibly have appeared before 1971. that was the year intel introduced the worlds first single-chip microprocessor. this chip, the 4004, was designed for use in a line of business calculators produced by the japanese company busicom. in 1969, busicom asked intel to design a set of custom integrated circuits, one for each of its new calculator models. the 4004 was intels response. rather than design custom hardware for each calculator, intel proposed a general-purpose circuit that could be used throughout the entire line of calculators. this general-purpose processor was designed to read and execute a set of instructionssoftwarestored in an external memory chip. intels idea was that the software would give each calculator its unique set of features and that this design style would drive demand for its core business in memory chips.the microprocessor was an overnight success, and its use increased steadily over the next decade. early embedded applications included unmanned space probes, computerized traffic lights, and aircraft flight control systems. in the 1980s and 1990s, embedded systems quietly rode the waves of the microcomputer age and brought microprocessors into every part of our personal and professional lives. most of the electronic devices in our kitchens (bread machines, food processors, and microwave ovens), living rooms (televisions, stereos, and remote controls), and workplaces (fax machines, pagers, laser printers, cash registers, and credit card readers) are embedded systems; over 6 billion new microprocessors are used each year. less than 2 percent (or about 100 million per year) of these microprocessors are used in general-purpose computers.it seems inevitable that the number of embedded systems will continue to increase rapidly. already there are promising new embedded devices that have enormous market potential: light switches and thermostats that are networked together and can be controlled wirelessly by a central computer, intelligent air-bag systems that dont inflate when children or small adults are present, medical monitoring devices that can notify a doctor if a patients physiological conditions are at critical levels, and dashboard navigation systems that inform you of the best route to your destination under current traffic conditions. clearly, individuals who possess the skills and the desire to design the next generation of embedded systems will be in demand for quite some time.3. real-time systemsone subclass of embedded systems deserves an introduction at this point. a real-time system has timing constraints. the function of a real-time system is thus partly specified in terms of its ability to make certain calculations or decisions in a timely manner. these important calculations or activities have deadlines for completion.the crucial distinction among real-time systems lies in what happens if a deadline is missed. for example, if the real-time system is part of an airplanes flight control system, the lives of the passengers and crew may be endangered by a single missed deadline. however, if instead the system is involved in satellite communication, the damage could be limited to a single corrupt data packet (which may or may not have catastrophic consequences depending on the application and error recovery scheme). the more severe the consequences, the more likely it will be said that the deadline is hard and thus, that the system is a hard real-time system. real-time systems at the other end of this continuum are said to have soft deadlinesa soft real-time system.嵌入式系统与rtos最近几十年里最令人惊讶的事，莫过于计算机逐渐占据了人类生活的主要地位。今天在我们的家里和办公室里，计算机的数量要比使用它们来生活和工作的人还要多，只是这些计算机里有很大一部分我们没有意识到它们的存在罢了。在这里，我将说明什么是嵌人式系统，以及可以在哪里找到它们。同附会介绍一下嵌人式编程的主题，说明一下为什么本书采用c 和c+语言讲述，另外简单介绍一下示例中所用到的硬件环境。1. 什么是嵌入式系统一个嵌入式系统(embedded system)就是一个计算机硬件和软件的集合体，也许还包括其他一些机械部件，它是为完成某种特定的功能而设计的。一个很好的例子就是微波炉。几乎每个家庭都有一台，并且每天都有上千万台微波炉在被人们使用着，但是很少有人意识到有处理器和软件在帮助他们做饭。这和家里的个人计算机形成了鲜明的对比。同样是由计算机硬件和软件，还有机械部件(比如硬盘)组成的，个人计算机却不是用来完成某个特定功能的。相反它可以做各种不同的事情。很多人用通用计算机来区分这一点。在发货的时候，通用计算机就像一块没有字的黑板，制造商并不知道用户要拿它来做什么。一个用户可能会用它来做文件服务器。另一个只用来玩游戏，还有一位可能会用它来写下一部伟大的美国小说。而嵌入式系统常常是一些更大的系统中的一个组成部分。比如，现代的轿车或卡车里就包含了很多嵌人式系统。一个嵌人式系统会被用来控制防刹车锁死，另一个监控车辆的气体排放情况，还有一个用来在仪表板上显示信息。虽然不是必需的，但在某些情况下，这些嵌人式系统会通过某种通信网络互相连起来。为了不至于混淆你的思路，有必要指出，通用计算机本身就是由很多嵌入式系统组成的。比如，我的电脑包含了键盘、鼠标、显示卡、调制解调器、硬盘、软盘和声卡，它们中的每一样都是一个嵌入式系统。每个设备都包含处理器和相应的软件来完成特定的功能。比如凋制解调器就是用来在模拟电话线上收发数字信号用的。正是如此，所有其他的设备也都能归纳出这么一句话来。如果一个嵌入式系统设计得很完善，那么它的使用者完全可以忽略它内部的处理器和软件的存在。微波炉、录像机和报时闹钟就是很好的例子。在某些情况下，用同样的功能的定制集成电路硬件来代替上面所说的处理器和软件，也能做出具有同样功能的设备来。不过，如果真是这样用纯粹的硬件来设计的话，在灵活性上就会丧失不少了，改几行软件怎么说也要比重新设计一块硬件电路来得方便和便宜。2. 过去和将来本章开头定义的嵌人式系统的第一个产品直到 1971 年以后才出现。