Embedded Systems Design 1

2 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 Design 3 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...

Embedded Systems Design 4 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.

Embedded Systems Design 5 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.

Embedded Systems Design 6 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.

Embedded Systems Design 7 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 Design 8 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, …

Embedded Systems Design 9 A “short list” of embedded systems List of Embedded Systems Anti-lock brakes Auto-focus cameras Automatic teller machines Automatic toll systems Automatic transmission Avionic systems Battery chargers Camcorders Cell phones Cell-phone base stations Cordless phones Cruise control Curbside check-in systems Digital cameras Disk drives Electronic card readers Electronic instruments Electronic toys/games Factory control Fax machines Fingerprint identifiers Home security systems Life-support systems Medical testing systems Modems MPEG decoders Network cards Network switches/routers On-board navigation Pagers Photocopiers Point-of-sale systems Portable video games Printers Satellite phones Scanners Smart ovens/dishwashers Speech recognizers Stereo systems Teleconferencing systems Televisions Temperature controllers Theft tracking systems TV set-top boxes VCR’s, DVD players Video game consoles Video phones Washers and dryers

Embedded Systems Design 10 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.

Embedded Systems Design 11 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 Systems Design 12 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.

Embedded Systems Design 13 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.

Embedded Systems Design 14 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 some interfaces to the outside world in the form of busses. What is missing? –Memory and the peripherals.

Embedded Systems Design 15 Block Diagram of a Microcomputer Too much. –For the limited applications intended, this system has too much of everything. Meaning – too expensive.

Embedded Systems Design 16 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?

Embedded Systems Design 17 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.

Embedded Systems Design 18 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.

Embedded Systems Design 19 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.

Embedded Systems Design 20 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.

Embedded Systems Design 21 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

Embedded Systems Design 22 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,# b ; 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,# b ; 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

Embedded Systems Design 23 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 !

Embedded Systems Design 24 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.

Embedded Systems Design 25 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.

Embedded Systems Design 26 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.

Embedded Systems Design 27 Why Not Use a Microprocessor? Processors vary in their customization for the problem at hand. total = 0 for i = 1 to N loop total += M[i] end loop General-purpose processor Single-purpose processor Application-specific processor Desired functionality