電氣及自動化專業(yè)外文翻譯(13)

1、中國地質(zhì)大學(xué)長城學(xué)院本科畢業(yè)論文外文資料翻譯學(xué) 院工程技術(shù)學(xué)院學(xué)生姓名齊業(yè)亮專 業(yè)電氣工程及其自動化學(xué) 號0431302152017年3月10日Using Linux in Embedded SystemsUNIX evokes a wide range of emotions: loved by some for its power and flexibility, despised by others for its eomplex and arcane commands. UNIX has established a checkered reputation in the world o

2、f computing.EASE OF USEUNIX is infamous for its glut of arcane , non-mnemonic, and cryptic keyboard commands, each with many command-line switches, which can be incredibly confusing to remember. Its SVR4 implementation contains more than 2,000 comands. Many of these functions can be combined, using

3、pipes and redirection. This illustrates one of UNIX 's design fundamentals: the creation of a large assortment of very specialized and modular commands that can be combined to accomplish complex tasks.While UNIX was essentially limited to use by software professionals at universities and in appl

4、ications development houses, its complex command-line syntax and resulting flexibility were considered an advantage rather than a problem.But this same flexibility also creates a major drawback for using UNIX in a business-oriented marketthe more flexible a system is, the more difficult it becomes t

5、o learn and operate.UNIX's script languages provide one form of help. Using scripts, a system administrator can tailor the system to a set of users'needs quickly.Another factor mitigating the difficulties of UNIX's arcane command language are the Graphic User Interfaces(GUIs), such as Mo

6、tif, SunView, or OpenLook. GUIs, however, place another level of incompatibility problems on what is already a complex system.Motif has been ported to the most different architectures and (because it follows the Presentation Manager style ) is perhaps closest in look and feel to a PC interface such

7、as Microsoft Windows. Sun View is also dominant because of its large installed base and the numbers of applications programmers who have become familiar with writing software to its specifications.BINARY COMPATIBILITYUNIX marketers have looked with some envy at the huge-base of shrink-wrapped applic

8、ations available in the DOS world and have promised that binary-compatible applications for systems is just around the corner. These promises have yet to be met in any significant way. While binary compatibility is not yet available, it is getting easier to share data and applications across differe

9、nt machines.PORTABILITYCompared with most operating system sources, UNIX code is quite move UNIX to different architectures. But a UNIX port to a new system is not a trivial matter, offen taking several man-years of work, and can result in glitches and malfunctions, which may create very subtle inco

10、nsistencies in performance. These bugs are often difficult to identify and correct.Having the source code available for your computer 's operating system is beneficial and detrimental: if the OS lacks certain desirable featuers, having the sources in-house greatly enhances a company's abilit

11、y to make necessary changes.On the other hand, the customized version of the operating system, with its new or modified features may later present compatibility problems with newer releases or purchased application.Why Linux?Intelligent dedicated systems and applicances used in interface, monitoring

12、 , communications, and control applications increasingly demand the services of a sophisticated, state-of-the-art operating systems. Many such systems require advanced capabilities like: high resolution and user-friendly graphical user interfaces(GUIs); TCP/IP connectivity; substitution of reliable(

13、 and low power)flash memory solid state disk for conventional disk drives; support for 32-bit ultra-high-speed CPUs; the use of large memory arrays; and seemingly infinite capacity storage devices including CD-ROMs and hard disks.This is not the stuff of yesteryear's “standalone”code, “roll-your

14、-own”kernels, or “plain old DOS”, No, those days are goneforever.Then too, consider the rapidly accelerating pace of hardware and chipset innovation accompanied by extremely rapid obsolescence of the older devices.Combine these two, and you can see why it 's become an enormous challenge for comm

15、ercial RTOS vendors to keep up with the constant churning of hardware devices . Supporting the newest devices in a timely mannereven just to stay clear of the unrelenting steamroller of chipset obsolescencetakes a large and constant resource commitment. If it' a struggle for the commercial RTOS

16、vendors to keep up, going it alone by writing standalone code or a roll-your-own kernel certainly makes no sense.With the options narrowing, embedded system developers find themselves faced with a dilemma:On the one hand, today's highly sophisticated and empowered intelligent embedded systemsbas

17、ed on the newest chips and hardware capabilitiesdemand noting less than the power, sophistication, and currency of support provided by a popular high-end operating system like windows.On the other hand, embedded systems demand extremely high reliability(for non-stop, unattended operation)plus the ab

18、ility to customize the OS to match an application's unique requirements.Linux 應(yīng)用于嵌入式系統(tǒng)UNIX 引起了全然不同的情緒：因其能力和靈活性而受到一些人的青睞，但因其 復(fù)雜且神秘的命令而受到另一些人的藐視。在計算世界里， UNIX 已建立起一個褒義 不一的聲譽。易用性UNIX 因其過于神秘、不易記憶和含義模糊的大量鍵盤命令而名聲不佳，這些命 令每個都有很多命令行開關(guān)，這可能造成昏藥而不易記憶。它的SVR4版本擁有2000多個命令，其中很多功能可通過管道和重定向進(jìn)行組合。這反映了UNIX 的基本設(shè)計思想之一：

19、 生成數(shù)量很大的專用和模塊化命令， 把它們結(jié)合起來就能完成各種復(fù)雜的 任務(wù)。雖然 UNIX 過去基本上限于大學(xué)和應(yīng)用開發(fā)公司中的軟件專業(yè)人員使用，其復(fù)雜 的命令行語法和由此而得到的靈活性被看作一個優(yōu)點而不是問題。但是在面向商業(yè)的市場中使用 UNIX，卻產(chǎn)生了一個重大的缺陷一一系統(tǒng)越靈活，它就變得越難學(xué)會和 操作。UNIX 的原本（或腳本）語言提供某種形式的幫助。利用原本語言，系統(tǒng)管理員 能很快地把系統(tǒng)裁剪成滿足一組用戶的需求?？朔?UNIX 神秘命令語言之困難的另一種方法是用圖形用戶接口 GUI， 如 Motif,SunView 或OpenLook。然而，圖形用戶接口在已經(jīng)很復(fù)雜的系統(tǒng)上增添了

20、另一 層不兼容性問題。Motif 已經(jīng)移植到差別非常大的不同體系結(jié)構(gòu)上（由于它仿效PresentationManager 的風(fēng)格），而且在外觀與感覺上也許是最接近于諸如 Microsoft Windows 一 類的PC接口。SunView由于有很大的裝機數(shù)和很多應(yīng)用程序員已熟悉按它的規(guī)范寫 軟件，所以也是一種主流圖形用戶接口。二進(jìn)制兼容性UNIX的銷售者以某種羨慕的心情關(guān)注著DOS世界中可能的大量簡裝應(yīng)用程序，并承諾不同系統(tǒng)的二進(jìn)制兼容的應(yīng)用程序即將面世。這些承諾遠(yuǎn)未讓人滿足。 雖然二進(jìn)制兼容性尚未獲得，但現(xiàn)在不同機器上共享數(shù)據(jù)和應(yīng)用程序正在變得更加容易。可移植性與多數(shù)操作系統(tǒng)源碼相比，UNI

21、X程序容易移植。它用C語言編寫，而不用匯編語言，使用UNIX能移植到不同的體系結(jié)構(gòu)上。 但是把UNIX移植到一個新系統(tǒng)上也不 是一件一蹴而就的事情，常常是要幾個人年的工作，還可能造成故障和失靈，從而在 性能上產(chǎn)生難以捉摸的不一致性。這些故障往往是難以識別與糾正的。擁有你自己的計算機操作系統(tǒng)的源碼，既有益，也有害；如果操作系統(tǒng)缺少某 些所需功能，公司自己擁有源碼能大大增強公司進(jìn)行必要修改的能力。另一方面，具有新的或修改特性的操作系統(tǒng)定制版本，在日后可能出現(xiàn)與更新 的版本或購買的應(yīng)用程序不兼容的問題。為什么用 LINUX？用于接口、監(jiān)控、通信和控制應(yīng)用程序的職能專用系統(tǒng)和設(shè)備越來越要求高級 的現(xiàn)代

22、操作系統(tǒng)的這些服務(wù)。 許多這樣的系統(tǒng)需要如下的高級性能： 高分辨率和用戶友好的圖形用戶界面： TCP/IP 鏈接；用可靠的閃存固態(tài)盤代替常規(guī)的磁盤機；支持32位的超高速 CPU使用大存儲器陣列；以及似乎是無限容量的存儲設(shè)備，包括CD-ROM和硬盤。這不是以前的獨立代碼，自己寫的核，或簡單的老是 DOS那些日子已永遠(yuǎn)過去。另外也考慮到硬件和芯片迅速加速的革新步伐伴隨著老設(shè)備相當(dāng)快地淘汰。結(jié)合這兩種情況， 就能知道為什么對商用實時操作系統(tǒng)供應(yīng)商而言， 跟上硬件設(shè)備的 不斷出新已變成巨大的挑戰(zhàn)。及時地支持最新設(shè)備，甚至不去理會不愿退讓的、大力 推銷的逐漸過時的芯片組， 你需要大量和不斷的資材投入。

23、如果商用實時操作系統(tǒng)供 應(yīng)商必須奮力緊跟硬件發(fā)展的話， 那么編寫?yīng)毩⒌拇a或?qū)懽约旱暮耍?這種單槍匹馬 的做法一定是毫無意義的。因為選擇范圍很小，嵌入式系統(tǒng)的開發(fā)商面臨這樣的一種困境： 一方面，今天高度復(fù)雜的，且授權(quán)的智能嵌入式系統(tǒng)（基于最新的芯片和硬件性 能）所需要的正式流行的高檔操作系統(tǒng)（如Windows）提供的那種能力、精致性，以及通用性。另一方面，嵌入式系統(tǒng)要求非常高的可靠性（不停機，無人照管的操作），加上有能力把操作系統(tǒng)改編成符合應(yīng)用系統(tǒng)的獨特的要求。其窘境是：通用桌面操作系統(tǒng)（如Windows）不能很好地適應(yīng)于類似設(shè)備的嵌入式系統(tǒng)的獨特需求。然而，商用實時操作系統(tǒng)，雖然設(shè)計成滿足嵌

24、入式應(yīng)用的可靠性 和配置靈活性的要求，但由于他們?nèi)狈?biāo)準(zhǔn)化以及沒有能力跟上技術(shù)的速度發(fā)展步 伐，它們?nèi)找娌缓闲枰ｉ_發(fā)人員做什么？幸運的是，一種新的、令人興奮的選擇系統(tǒng)已經(jīng)出現(xiàn)：開放源碼Linux 。 Linux提供功能強大的和高級系統(tǒng)管理設(shè)施。豐富的設(shè)備支持，在可靠性和魯棒性，以及廣 泛詳盡的文檔方面有極好的聲譽。最好的（對系統(tǒng)開發(fā)人員而言）是Linux 不要錢有完全免費的源代碼。Linux是不是像 Windows那樣太大以及需要系統(tǒng)資源太多，以致不能滿足嵌入式 系統(tǒng)的約束要求呢？與Windows不同，Linux本來就是模塊化的，并且能夠很容易縮減成緊縮配置，這種配置幾乎與DOS差不多大，甚

25、至能放到一張軟盤上。此外，因為Linux 源碼是免費可用的，所以可以按照獨特的嵌入式系統(tǒng)要求改編該操作系統(tǒng)。這樣，并不令人驚奇， 開放源碼 Linux 已建成了一個新的操作系統(tǒng)開發(fā)和支持范 例，在那里數(shù)以千計的開發(fā)人員繼續(xù)貢獻(xiàn)于不斷發(fā)展的Linux 代碼庫。此外，幾十家面向 Linux 的軟件公司已經(jīng)出現(xiàn)他們熱切支持那些為建立從工廠自動化到智能 設(shè)備范圍很廣的應(yīng)用系統(tǒng)的開發(fā)人員的要求。Linux對許多嵌入式系統(tǒng)，為了適應(yīng)諸如 RAM固態(tài)盤、處理機速度，以及功耗 的約束，嵌入的 Linux 的主要任務(wù)是，使系統(tǒng)所需的資源最小。嵌入式操作系統(tǒng)可能 需要從一個芯片盤或緊湊閃存固態(tài)盤上自舉；或者自舉和

26、運行在沒有顯示器和鍵盤 （“無頭”操作）的環(huán)境，或經(jīng)有以太網(wǎng)連接，從遠(yuǎn)程設(shè)備裝入應(yīng)用程序?，F(xiàn)成的小 Linux 有許多來源， 其中有日益增多的面向應(yīng)用的 Linux 配置和分發(fā)版， 這些都被修改成適應(yīng)于特定的應(yīng)用。例如路由器、防火墻、互聯(lián)網(wǎng)/ 網(wǎng)絡(luò)設(shè)備、網(wǎng)絡(luò)服務(wù)器、網(wǎng)關(guān)等。你也可能選擇建立你自己喜歡的嵌入式 Linux ，從一個標(biāo)準(zhǔn)分發(fā)版開始，略去不 要的模塊。雖然如此，還應(yīng)該考慮從別人的工作配置基礎(chǔ)上開始你的工作，因為他們 的版本的源僅是完全合法的，而且也是被鼓勵。實時 Linux許多嵌入式系統(tǒng)需要對現(xiàn)實世界的一些事件可預(yù)測，并且受限響應(yīng)。這樣的實時 系統(tǒng)包括工廠自動化、數(shù)據(jù)采集和控制系統(tǒng)、

27、音頻 / 視頻應(yīng)用，以及許多其他計算機 化的產(chǎn)品和設(shè)備。什么是“實時系統(tǒng)”？通常接受的“實時”性能的定義是，現(xiàn)實世 界時間必須在確定的、可預(yù)測的，以及在相對短的時間間隔內(nèi)得到響應(yīng)。雖然 Linux 不是一個實時操作系統(tǒng) （ Linux 內(nèi)核不提供所需要的事件優(yōu)先級和搶 占功能），但當(dāng)前有幾個擴充選項可用， 這些選項把實時能力帶給基于 Linux 的系統(tǒng)， 最通常的方法是雙內(nèi)核方法。用這個方法，通用（非實時） OS 運行作為實時內(nèi)核的 一個任務(wù)。通用操作系統(tǒng)提供諸如磁盤讀/寫、LAN/通信、串行/并行I/O、系統(tǒng)初始化、內(nèi)存管理等功能，而實時內(nèi)核處理時限世界事件。你可以把這個看作兩者兼得， 因為

28、它能夠保持流行的通用操作系統(tǒng)好處，而增加了實時 OS的能力。就Linux來說,你能保持與標(biāo)準(zhǔn) Linux 兼容，而以非干擾的方式增加了實時功能。當(dāng)然，也可以專研并修改 Linux ，把改變成實時操作系統(tǒng)，因為它的源碼是公開 可用的，但如果這樣做，你會面臨這樣嚴(yán)重缺點，即不論特性方面，還是驅(qū)動程序方 面都不能與主流 Linux 同步前進(jìn)。 簡言之， 你的制定 Linux 將不能從 Linux 的不斷進(jìn) 展中獲得好處，而這種進(jìn)展是世界范圍內(nèi)數(shù)以千計的開發(fā)人員共同協(xié)力的結(jié)果。Linux 是一個操作系統(tǒng)，它擔(dān)當(dāng)計算機系統(tǒng)硬件與軟件間的通信服務(wù)，Linux 內(nèi)核包含了你在任何操作系統(tǒng)所期望的所有特性。A

29、 Low-Cost, Smart Capacitive Position Sensor Abstract：A new high-performance, low-cost, capacitive position-measuring system is described. By using a highly linear oscillator, shielding and a three-signal approach, most of the errors are eliminated. The accuracy amounts to 1卩 m ovreng. Since the outp

30、ut of the oscillatorcan directly be connected to a microcontroller, an A/D converter is not needed.I. INTRODUCTIONThis paper describes a novel high-performance, low-cost, capacitive displacement measuring system featuring:1 mm measuring range,1 卩 m accuracy,0.1 s total measuring time.Translated to t

31、he capacitive domain, the specifications correspond to:a possible range of 1 pF;only 50 fF of this range is used for the displacement transducer;50 aF absolute capacitance-measuring inaccuracy.Meijer and Schrier l and more recently Van Drecht,Meijer, and De Jong 2 have proposed a displacement-measur

32、ing system, using a PSD (Position Sensitive Detector) as sensing element. Some disadvantages of using a PSD are the higher costs and the higher power consumption of the PSD and LED (Light-Emitting Diode) as compared to the capacitive sensor elements described in this paper.The signal processor uses

33、the concepts presented in 2,but is adopted for the use of capacitive elements. By the extensive use of shielding, guarding and smart A/D conversion,the system is able to combine a high accuracy with a very low cost-price. The transducer produces three-period-modulated signals which can be selected a

34、nd directly read out by a microcontroller. The microcontroller,in return, calculates the displacement and can send this value to a host computer (Fig. 1) or a display or drive an actuator.CxFig. 1. Block diagram of the systemC refWe tai Shieldin?Fig. 2. Perspective and dime nsions of the electrode s

35、tructureII . THE ELECTRODE STRUCTUREThe basic sensing element consists of two simple electrodes with capacitanee Cx, (Fig. 2). The smaller one (E2) is surro un ded by a guard electrode. Thanks to the use of the guard electrode, the capacitanee Cx between the two electrodes is independent of movement

36、s (lateral displaceme nts as well as rotati ons) parallel to the electrode surface.The in flue nee of the parasitic capacitances Cp will be eliminated as will be discussed in Sectioffi .Accordi ng to Heere ns 3, the relative deviati on in the capacita nee Cx betwee n the two electrodes caused by the

37、 finite guard electrode size is smaller than:S <et (x/d)(1)where x is the width of the guard and d the distance between the electrodes. This deviationintroduces a nonlinearity.Therefore we require that 3 is less than 100 ppm.Also the gap betwee n the small electrode and the surro unding guard cau

38、ses a deviatio n:3 <冗(d/s)with s the width of the gap. This deviati on is n egligible compared to (l), whe n the gap width is less tha n 13 of the dista nee betwee n the electrodes.Another cause of errors originates from a possible finite skew angle a between the two electrodes (Fig. 3). Assu min

39、g the follow ing con diti ons:the potentials on the small electrode and the guard electrode are equal to 0 V,the pote ntial on the large electrode is equal to V volt,the guard electrode is large eno ugh,it can be seen that the electric field will be concentric.Fig. 3. Electrodes with angle . aTo kee

40、p the calculations simple, we will assume the electrodes to be infinitely large in one direct ion. Now the problem is a two-dime nsio nal one that can be solved by using polar-coord in ates (r, © ). In this case the electrical field can be described by:V sinV costo 0 and in tegrate over r:To ca

41、lculate the charge on the small electrode, we set with Bl the left border of the small electrode:Bl td12(5)and Br the right border:BrdlSol ving (4) results in:tan20 .2d cosl sinQ V lna2d cosl sinFor small a's this can be approximated by:(8)C右JIt appears to be desirable to choose l smaller than d

42、, so the error will depend only on theangle a .In our case, a change in Omgle of 0.6will cause an error less than 100 ppm.With a proper design the parameters£ o and l are constant,and then the capacitanee betweenthe two electrodes will depe nd only on the dista nee d betwee n the electrodes.川.E

43、LIMINATION OF PARASITIC CAPACITANCESBesides the desired sensor capacitanee C, there are also many parasitic capacitances in the actual structure (Fig.2). These capacitances can be modeled as shown in Fig.4. Here Cpl represe nts the parasitic capacita nces from the electrode E1 and Cp2 from the elect

44、rode E2 to the guard electrodes and the shielding. Parasitic capacitance Cp3 results from imperfect shieldi ng and forms an offset capacita nce. When the tran sducer capacita nce Cx is conn ected to an AC voltage source and the current through the electrode is measured,Cpl and Cp2 will be elim in at

45、ed. Cp3 can be elimi nated by perform ing an offset measureme nt.Fig. 4. Elimination of parasitic capacitancesThe current is measured by the amplifier with shunt feedback, which has a very low input impedanee. To obtain the required linearity, the unity-gain bandwidth fT of the amplifier has to sati

46、sfy the following condition:12Cf(9)CfC p2where T is the period of the in put sig nal.Since Cp2 con sists of cable capacita nces and the in put capacita nee of the op amp, it may in deed be larger tha n Cf and can not be n eglected.IV. THE CONCEPT OF THE SYSTEMThe system uses the three-sig nal con ce

47、pt prese nted in 2, which is based on the follow ing principles. When we measure a capacitor Cx with a linear system, we obtain a value:(10)M x mCx M Offwhere m is the unknown gain and Moff, the unknown offset.By perform ing the measureme nt of a refere nee qua ntity Cref, i n an ide ntical way and

48、by measuri ng the offset, Moff,by mak ing m = 0, the parameters m and Moff are eliminated.The final measurement result P is defined as:(11)(12)p M ref M off Mx M offIn our case, for the sensor capacitance C, it holds that:Adodwhere Ax is the area of the electrode, do is the in itial dista nce betwee

49、 n them,constant and d is the displacement to be measured. For the reference electrodes it holds that:C refAref d ref(13)with Aref the area and dref the distance. Substitution of (12) and (13) into (10) and then into (11) yields:Aref do dAxdrefda1 a0d ref(14)Here, P is a value representing the posit

50、ion while a1 and a0 are unknown, but stable constants. The constant a1 =Aref/Ax is a stable constant provided there is a good mechanical matching between the electrode areas. The constant ao = (Arefd0/(Axdref) will also be a stable constant provided that do and dref are constant. These constants can

51、 be determined by a one-time calibration. In many applications this calibration can be omitted; when the displacement sensor is part of a larger system, an overall calibration is required anyway. This overall calibration eliminates the requirement for a separate determination of a1 and a0.V . THE CA

52、PACITANCE-TO-PERIOD CONVERSIONThe signals which are proportional to the capacitor values are converted into a period, using a modified Martin oscillator 4 (Fig. 5j.When the voltage swing across the capacitor is equal to that across the resistor and the NAND gates are switched off, this oscillator ha

53、s a period Toff:Toff = 4RCoff. (15)Since the value of the resistor is kept constant, the period varies only with the capacitor value. Now, by switching on the right NAND port, the capacitance CX can be connected in parallel to Coff. Then the period becomes:Tx=4R(Coff+Cx)=4RCx+Toff (16)The constants

54、R and Toff are eliminated in the way described in Section IV.In 2 it is shown that the system is immune for most of the nonidealities of the op amp and the comparator, like slewing, limitations of bandwidth and gain, offset voltages,and input bias currents. These nonidealities only cause additive or

55、 multiplicative errors which are eliminated by the three-signal approach.一種低成本智能式電容位置傳感器摘要：本文描述了一種新的高性能，低成本電容位置測量系統(tǒng)。通過使用高線性振蕩器， 屏蔽和三信號通道，大部分誤差被消除。其精確度在1毫米范圍內(nèi)達(dá)1微米。由于振蕩器的輸出可直接連接到微控制器，所以無需用A/D轉(zhuǎn)換器。I .導(dǎo)言本文介紹了一種新型高性能，低成本的電容位移測量系統(tǒng)，特點如下：1毫米測量范圍1微米精確度0.1 s總測量時間對應(yīng)到電容域，規(guī)格相當(dāng)于：1皮法的變化范圍；只有這個范圍的 50fF （fF是法拉乘以10的負(fù)1

56、5次方。f是femto 的縮寫）用于位移傳感器。50aF絕對電容測量誤差。梅耶爾和施里爾1以及最近的范德雷赫特河，梅耶爾，和德容2提出了位移測量系統(tǒng)， 采用一個PSD（位置敏感探測器）作為傳感元件。和本文描述的電容傳感器元件相比，使 用PSD的缺點是，PSD和 LED（發(fā)光二極管）有更高的成本和功率消耗。使用2中所提概念的信號處理器，被采用到電容元件的使用中。通過廣泛使用屏蔽， 智能A/ D轉(zhuǎn)換，該系統(tǒng)能夠?qū)⒏呔_度和低成本結(jié)合。換能器產(chǎn)生可以選擇和直接由微 控制器讀出的三段調(diào)制信號。微控制器，相應(yīng)的，計算位移及發(fā)送此值到主機電腦（圖 1） 或顯示或驅(qū)動執(zhí)行器。CxC ref圖1該系統(tǒng)的框圖金屬 屏蔽圖2電極結(jié)構(gòu)的尺寸和透視圖