Embedded Systems Design 1. 2 Embedded Systems Overview Computing systems are everywhere Most of us think of “desktop” computers –PC’s –Laptops –Mainframes.

Embedded Systems Design 1

Embedded Systems Design


Embedded Systems Overview

• Computing systems are everywhere

• Most of us think of “desktop” computers– PC’s– Laptops– Mainframes– Servers

• But there’s another type of computing system– Far more common...


Embedded Systems Overview

• Embedded computing systems:– Computing systems embedded

within electronic devices.– Hard to define. Nearly any

computing system other than a desktop computer.

– Billions of units produced yearly, versus millions of desktop units.

– Perhaps 50 per household and per automobile.

and here...

and even here...

Lots more of these, though they cost a lot

less each.

Computers are in here...


Common Characteristics of Embedded Systems

• Single-functioned– Executes a single program, repeatedly.

• Tightly-constrained– Low cost, low power, small, fast, etc.

• Reactive and real-time– Continually reacts to changes in the system’s

environment.– Must compute certain results in real-time without

delay.


Design Constraints

• Limited Power.– Most embedded systems operate within battery operated

equipment.

• Limited Memory.– An embedded system is constrained to a finite and small

amount of memory.

• Real-Time.– Most embedded systems are used in a control function. – They are expected to sense the real-time status of the

system in which they are housed and produce real-time responses.


Definition of Embedded System

• An embedded system is a microprocessor-based system that is built to control a function or range of functions and is not designed to be programmed by the end user.– The user may make choices concerning the

functionality of the system but cannot change the functionality of the system by adding/replacing software.

– Can you “program” your refrigerator?• May be sooner than you think.


Definition of Embedded System

An embedded system is not a microprocessor used in a

“traditional” computing application

– desktop PC

– laptop

– workstation

An embedded system is a microprocessor used as a

component in another piece of technology (dedicated

function)


Embedded Systems : Applications

• Consumer segment, e.g. digital cameras, camcorders, VCRs, Washing Machines, microwave ovens, …

• Automobiles, e.g., engine control, anti-lock brake, air bags, …

• Office automation, e.g., copiers, printers, FAX machines, …• Telecommunications, e.g.,, cellular phones, PDAs,

interactive game boxes, answering machines, …• Other industrial products, e.g., door locks in hotel rooms,

automatic faucets, …


A “short list” of embedded systemsList of Embedded Systems

Anti-lock brakesAuto-focus camerasAutomatic teller machinesAutomatic toll systemsAutomatic transmissionAvionic systemsBattery chargersCamcordersCell phonesCell-phone base stationsCordless phonesCruise controlCurbside check-in systemsDigital camerasDisk drivesElectronic card readersElectronic instrumentsElectronic toys/gamesFactory controlFax machinesFingerprint identifiersHome security systemsLife-support systemsMedical testing systems

ModemsMPEG decodersNetwork cardsNetwork switches/routersOn-board navigationPagersPhotocopiersPoint-of-sale systemsPortable video gamesPrintersSatellite phonesScannersSmart ovens/dishwashersSpeech recognizersStereo systemsTeleconferencing systemsTelevisionsTemperature controllersTheft tracking systemsTV set-top boxesVCR’s, DVD playersVideo game consolesVideo phonesWashers and dryers


Advantages of Microprocessor-based

• Replacement of discrete logic-based circuits.

• Provide functional upgrades.

• Provide easy maintenance upgrades.

• Improve mechanical performance.

• Protection of intellectual property (IP).

• Replacement of analog circuits.


Elements of an Embedded System

• Processor

• Memory– Provide storage for the software and data.

• Peripherals

• Software– Initialization and Configuration.– Operating System.– The application software.– Error handling.– Debug and maintenance support.


Embedded System Microcontroller

• Embedded systems are mainly intended to provide control over the behavior of the system into which they are housed.– Therefore, it is customary to talk about an

embedded controller rather than an embedded processor.

– It does process information but mainly for the purpose of control.

• When all hardware required to run the application is provided on one chip, it is referred to as an embedded microcontroller or in short microcontroller.


What is a Microcontroller ?

• A microcontroller is a single chip microprocessor system which contains:

– A processor core.– Data and program memory.– Serial and parallel I/O.– Timers.– External and internal interrupt handling

mechanism.

all integrated into a single chip.


Block Diagram of a Microprocessor

• A microprocessor consists of an ALU to perform arithmetic and logic manipulations, registers, and a control unit.

• In addition,its has someinterfaces tothe outsideworld in theform of busses.

• What is missing?– Memory and the peripherals.


Block Diagram of a Microcomputer

• Too much.– For the limited applications intended, this system has too

much of everything.• Meaning – too expensive.


How do we Define Expensive?• Money.

– The system requires parts that cost too much money.

• Size.– All of the additional functionality requires space.

• Chip area or board space.

• Power.– We will need power to run all of these chips and devices.

• Heat.– Power = heat.– Operating “inside” another system may not afford us good

heat dissipation.

• Efficiency.– Are we really utilizing all of these features and

functionalities?


Block Diagram of a Microcontroller

• It is the specialized circuitry compared to the microprocessor that makes the microcontroller such a unique device.

• The microcontroller operates on data that is fed in through its serial or parallel input ports controlled by the software stored in the on-chip memory.


Special Features of the Microcontroller• All of the additional functions built into the microcontroller

would normally require additional circuitry external to the microprocessor.– I/O Ports.– Memory.

• Some of these functions would normally be implemented in software.– Counters, timers.

• We can include them in the microcontroller chip after removing some of the un-necessary functions.– Floating point functions.– Specialized multimedia instructions.


Memory Considerations

• When a PC executes an application, pieces of the application are read from disk and stored into an allocated section of the memory.– As more of the program is needed, additional

pieces of the software are loaded into the memory.

• In a microcontroller there is no disk to read from. On-chip ROM space is the maximum size of the application that can be executed.


Additional Programming Considerations

• In a standard computer, there is a complicated operating system that handles all low-level operations.– Things like reading from interfacing to the different

devices, and allocating memory.

• For an embedded system, the application stored in the ROM of the microcontroller is the only software that will execute.– Therefore, all low-level code and device interfaces

necessary to execute the application have to be included.


Example of a PC program

• This code simply calls the operating system that will print the message stored at the location “Msg” and returns execution to the operating system.

• To execute this program in a microcontroller, this code would be considerably longer...

MAIN:

mov AH, 9 ; Program start

lds DX, Msg ; Print message

int 021h

mov AH, 04Ch ; End the program

xor AL, AL ; with a return code

int 21h ; of “0”

Msg db “Hello World”, 00Dh, 00Ah, 0


Example of a microcontroller program

• Because the display subroutine including its initialization has to be written.

• The software has also to know where the device is connected to and to make sure that the device is connected properly.

LCD_INIT proc

setb B_LCDONOFF ; LCD Display On

clr B_LCDCURSOR ; Cursor Off

clr B_LCDBLINK ; No Blinking

;

call IO_LCDEN_LO ; Clear LCD Enable

call l?p1 ; Send Init Byte

call l?p1 ; Send Init Byte, Again



call LCD_DMOD ; Set Display Mode

call LCD_CLEAR ; Clear Display

call LCD_WAIT ; Wait For Display To Finish

mov a,#00000110b ; Entry Mode, Increase With No Shifting

call LCD_IOC ; Strobe Data To Display

mov D_LCDPOS,#000h ; Set Initial Cursor To 0

ret ; Return To Caller

;

l?p1 mov a,#00110000b ; Function Set, 8 Bits, 1 Line, 5 x 7 Dots

call LCD_IOC ; Strobe Data To LCD Display

mov r3,#0ffh ; R3 = ff

mov r2,#0ffh ; R2 = ff

l?p2 djnz r3,l?p2 ; Loop

djnz r2,l?p2 ; Waste More Than 4.1 Ms

ret ; Return To Caller

endproc


Microcontroller vs. Microprocessor

• Microprocessor (P):– Designed to perform as a CPU in a microcomputer

system.– The instruction set is arranged to allow code and

large amounts of data to be moved between the P and the external memory and registers.

– Operations on not less than four bits.

• Microcontroller (C):– Designed to operate with minimum of external

circuitry.– Simple instruction set (255 instructions).– Operations possible on single bits !


Where are microcontrollers used ?

• Microcontrollers are “typically” used where processing power is not critical.

• It is estimated that on average a middle-class household has a minimum of 35 microcontrollers in it.

• About 34 % of microcontroller applications are in office automation such as laser printers, fax machines, intelligent telephones and so forth.

• Another 33 % of microcontrollers are used in consumer electronic goods such as CD players and hi-fi equipment.

• The remaining 33 % are used in the communications and automotive market.


Evolution of microcontrollers

• Microcontroller evolved from a board-level design to a single chip in the mid-1970's. As the process of miniaturization continued, all of the components needed for a controller were built right onto one chip.

• In the mid-1980’s embedded systems migrated from the single chip to microcontrollers embedded into a larger ASIC (Application Specific Integrated Circuit) design.


Advantages of using microcontrollers• Fast and effective

– The architecture correlates closely with the problem being solved (control systems).

• Low cost / Low power– High level of system integration within one component. – Only a handful of components needed to create a working

system.

• Compatibility– Opcodes and binaries are the SAME for all 80x51 variants.

• Multi-sourced– Over 12 manufacturers, hundreds of varieties.

• Constant improvements– Improvements in silicon/design increase speed and power

annually.


Why Not Use a Microprocessor?

• Processors vary in their customization for the problem at hand.

total = 0for i = 1 to N loop total += M[i]end loop

General-purpose processor

Single-purpose processor

Application-specific processor

Desired functionality

Embedded Systems Design 1. 2 Embedded Systems Overview Computing systems are everywhere Most of us think of “desktop” computers –PC’s –Laptops –Mainframes.

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