1、UNIT13 Embedded System 13-1 Technical Part13-2 Reading Material 13-1 Technical Part13-1-1 Definition An embedded system is a computer system designed for specific control functions within a larger system,often with real-time computing constraints(See Figure 13-1).It is embedded as part of a complete
2、 device often including hardware and mechanical parts.By contrast,a general-purpose computer,such as a personal computer(PC),is designed to be flexible and to meet a wide range of end-user needs.Embedded systems control many devices in common use today.13-1-2 IntroductionsComponents of an Embedded S
3、ystemAn embedded system is one that has computer-hardware with software embedded in it as one of its most important component.It is a dedicated computer-based system for an application(s)or product.It may be either an independent system or a part of a larger system.As its software usually embeds in
4、ROM(Read Only Memory)it does not need secondary memories as in a computer.An embedded system has three main components:Figure 13-1 Picture of the internals of an ADSL modem/router.A modern example of an embedded system.Labelled parts include a microprocessor(4),RAM(6),and flash memory(7).1.It has ha
5、rdware.Figure 13-2 shows the units in the hardware of an embedded system.Figure 13-2 the Components of an Embedded System Hardware2.It has main application software.The application software may perform concurrently the series of tasks or multiple tasks.3.It has a Real Time Operating System(RTOS)that
6、 supervises the application software and provides a mechanism to let the processor run a process as per scheduling and do the context-switch between the various processes(tasks).RTOS defines the way the system works.It organizes access to a resource in sequence of the series of tasks of the system.I
7、t schedules their working and execution by following a plan to control the latencies and to meet the deadlines.Latency refers to the waiting period between running the codes of a task and the instance at which the need for the task arises.It sets the rules during the execution of the application sof
8、tware.A small-scale embedded system may not need an RTOS.An embedded system has software designed to keep in view three constraints:(i)available system memory,(ii)available processor speed and(iii)the need to limit power dissipation when running the system continuously in cycles of wait for events,r
9、un,stop and wake-up.Characteristics of Embedded System1.Embedded systems are designed to do some specific task,rather than be a general-purpose computer for multiple tasks.Some also have real-time performance constraints that must be met,for reasons such as safety and usability,others may have low o
10、r no performance requirements,allowing the system hardware to be simplified to reduce costs.2.Embedded systems are not always standalone devices.Many embedded systems consist of small,computerized parts within a larger device that serves a more general purpose.For example,the Gibson Robot Guitar fea
11、tures an embedded system for tuning the strings,but the overall purpose of the Robot Guitar is,of course,to play music.Similarly,an embedded system in an automobile provides a specific function as a subsystem of the car itself.3.The program instructions written for embedded systems are referred to a
12、s firmware,and are stored in read-only memory or Flash memory chips.They run with limited computer hardware resources:little memory,small or non-existent keyboard or screen.Classification of Embedded SystemsWe can classify embedded systems into three types as follows:1.Small Scale Embedded Systems:T
13、hese systems are designed with a single 8-or 16-bit microcontroller,they have little hardware and software complexities and involve board-level design.They may even be battery operated.When developing embedded software for these,an editor,assembler and cross assembler,specific to the microcontroller
14、 or processor used,are the main programming tools.Usually,C is used for developing these systems.C program compilation is done into the assembly,and executable codes are then appropriately located in the system memory.The software has to fit within the memory available and keep in view the need to l
15、imit power dissipation when system is running continuously.2.Medium Scale Embedded Systems:These systems are usually designed with a single or few 16-or 32-bit microcontrollers or DSPs or Reduced Instruction Set Computers(RISCs).These have both hardware and software complexities.For complex software
16、 design,there are the following programming tools:RTOS,Source code engineering tool,Simulator,Debugger and Integrated Development Environment(IDE).Software tools also provide the solutions to the hardware complexities.An assembler is of little use as a programming tool.These systems may also employ
17、the readily available ASSPs and IPs for the various functionsfor example,for the bus interfacing,encrypting,deciphering,discrete cosine transformation and inverse transformation,TCP/IP protocol stacking and network connecting functions.ASSPs and IPs may also have to be appropriately conFigured by th
18、e system software before being integrated into the system-bus.3.Sophisticated Embedded Systems:Sophisticated embedded systems have enormous hardware and software complexities and may need scalable processors or configureurable processors and programmable logic arrays.They are used for cutting edge a
19、pplications that need hardware and software co-design and integration in the final system,however,they are constrained by the processing speeds available in their hardware units.Certain software functions such as encryption and deciphering algorithms,discrete cosine transformation and inverse transf
20、ormation algorithms,TCP/IP protocol stacking and network driver functions are implemented in the hardware to obtain additional speeds by saving time.Some of the functions of the hardware resources in the system are also implemented by the software.Development tools for these systems may not be readi
21、ly available at a reasonable cost or may not be available at all.In some cases,a compiler or retargetable compiler might have to be developed for these.A retargetable compiler is one that conFigures according to the given target conFigureuration in a system.Embedded Operating SystemAn embedded opera
22、ting system(EOS)is a system software that manages all the other programs and devices in an embedded system.It normally guarantees a certain capability within a specified storage size and time constraint as well as with application programs.Its structure is very similar to a structure of a normal ope
23、rating system however mainly differentiated by some factors such as type of preinstalled device,functional limits,taking designed job only.It also normally has boot loader,OS kernel,required device drivers,file systems for the user data and so forth.At their core,embedded operating systems contain s
24、ome of the same software components used on larger operating systems,such as windows and Linux etc.larger operating systems(OS),embedded operating systems deals with task switching,scheduling of tasks,memory allocation,etc.But there are some distinctions between desk top computer OS and embedded sys
25、tem OS.Desktop Computer is a general purpose computing system whereas embedded system purpose is for a specific task.Embedded operating systems have several common characteristics that distinguish such systems from other computing systems:Single Functioned:Usually executes a specific program repeate
26、dly e.g.pager.Tightly Constrained:All computing systems have constraints on design metrics,but those on embedded systems can be especially tight.A design metric is a measure of an implementations features,such as cost,size,performance and power.Reactive and Real Time:Many embedded systems must conti
27、nually react to changes in the systems environment and must compute certain results in real time without delay.In contrast,a desktop system typically focuses on computation with relatively infrequent reactions to input devices.Secondary Memory:Generally embedded system doesnt need secondary memory.U
28、nlike a desktop computer system which may have new software loaded onto it frequently,embedded systems retain the same code for a long time,sometimes indefinitely.Embedded operating systems do not usually include support for external storage or graphical interfaces,or protection from malicious or un
29、stable code.The limited memory in embedded systems requires the operating system and process to work very closely to manage the free resources.13-1-3 Application Case or Example Washing MachineWashing machine supports three functional modes:1.Fully Automatic Mode:In fully automatic mode,once the sys
30、tem is started it perform independently without user interference and after the completion of work it should notify the user about the completion of work.This mode instantaneously sense cloth quality and requirement of water,water temperature,detergent,load,wash cycle time and perform operation acco
31、rdingly.2.Semi Automatic Mode:In this semiautomatic mode in which washing conditions are predefined.Once the predefined mode is started the system perform its job and after completion it inform the user about the completion of work.3.Manual Mode:In this mode,user has to specify which operation he wa
32、nts to do and has to provide related information to the control system.For example,if user wants to wash clothes only,he has to choose wash option manually.Then the system ask the user to enter the wash time,amount of water and the load.After these data are entered,the user should start the machine.
33、When the specified operation is completed system should inform the user.Remember that Modes should be a selectable by a keypad.A washing machine may have a System Controller(Brain of the System)which provides the power control for various monitors and pumps and even controls the display that tells u
34、s how the wash cycles are proceeding.A washing machine comprises several components as shown in Figure 13-3.Figure 13-3 the components of washing machineThe working of these components is as follows:1.Display Panel:It is a touch panel screen to control all the operations of a machine 2.Sensor:It mea
35、sures the water level and appropriate amount of soap.Input devices for automatic washing machine are sensors for water flow,water level and temperature,door switch,selector knob or buttons for settings such as spin speed,temperature,load size and types of wash cycle required.Water Level Sensor:It in
36、dicates beep sound when water level is low in washing tub.Door Sensor:It indicates beep sound when all clothes are washed that means now you can open the maching door and also you can move to your next phase.Next phase will be dry Phase.This phase also follows same concept for drying the clothes.3.D
37、riving Motor:Motor can rotate in two directions either“reverse or forward.The forward direction drives the current in forward direction and motor rotates forward.The reverse direction driver does the opposite of it.A washing machine can maintain single motor in fully automatic or double motor in sem
38、i automatic washing machine.Sequence of washing the clothes with this can be explained in few steps as follows:1)Put on your dirty clothes on to the wash tub for washing.2)Put the detergent Soap(of your choice like Surf n Excel etc.).3)Put ON the tap,water rushes inside the tub.4)If its electronic c
39、ontrol,then by the press of the keys,you could program,if its mechanical it shall something like an mechanical switches wherein you are allowed to operate for setting the wash time.5)Now the wash motor rotates and washes the clothes and gives you a beep sound 6)Now your clothes are washed remove it
40、from the wash tub and put it on the spin tub and program it accordinglyafter spinning clothes are dried and you are allowed to hang it for proper drying in sunlight.The fully automatic also comes in two category front loading as well as top loading.1)Front loading is the one wherein you are given an
41、 opening to put clothes in on the front side.2)Top loading is on the top.4.System Controller:Such Component is used to control the motor speed.Motor can move in forward direction as well as reverse direction.System Controller reads the speed of motor and controls the speed of motor in different phas
42、es such as in washing,cleaning,drying etc.All kinds of Sensors such as Door Sensor,Pressure Sensor and Keypad,Speed sensor are also maintained by this.5.Water Pump:The water pump is used to recirculate water and drain out the dirty water.This pump actually contains two separate pumps inside one:The
43、bottom half of the pump is hooked up to the drain line,while the top half recirculates the wash water.The motor that drives the pump can reverse direction.It spins one way when the washer is running a wash cycle and recirculates the water,and it spins the other way when the washer is doing a spin cy
44、cle and draining the water.13-2 Reading Material 13-2-1 Reading comprehensionTrend of Tiny Embedded SystemsSignificant advances in microelectronics technology made the increasing miniaturization of embedded systems possible.This trend to miniaturization began in the late 1960s and,as stated by Moore
45、s Law that the power of microprocessors doubles about every 18 months,has held true with astonishing accuracy and consistency until the beginning of the 21st century.An announcement like that by IBM concerning the use of 29.9 nm technology to print circuits indicates that this trend will continue fo
46、r a number of chip generations.The trend is leading to and will result in the development of tiny embedded systems,integrated into more and more everyday objects.And will create a world of smart devices surrounding us.For example,parents will no longer lose track of their children,even in the busies
47、t crowds,when location sensors and communication modules are sewn into their clothes.Similar devices attached to timetables and signposts could guide blind or foreign people in unknown environments by talking to them.Another interesting possibility offered by such technology would be the creation of
48、 intelligent homes where a refrigerator can detect old food,a washing machine can query the instructions for dirty clothes,or window and door handles indicate whether they are open or closed.This concept called ambient intelligence,where humans have computing and networking technology embedded in th
49、eir surroundings,was developed by the ISTAG advisory group.While this vision may sound utopian when you first hear about it,current technology is already at a stage where it is possible to realize it.Ambient intelligence requires that there be thousands of tiny embedded devices in the environment.Ea
50、ch of these devices require some source of power for it to function.While power can be sent to them through cables or batteries,neither of these possibilities offers an effective and long term solution.The large number of these devices makes it highly desirable that they be fully self-sustaining and
