EMBEDDED SYSTEMS

UNIT – I

Introduction to functional building blocks of embedded systems Register,

memory devices, ports, timer, interrupt controllers using circuit block diagram

representation for each categories.

1.1 INTRODUCTION TO EMBEDDED SYSTEM

OBJECTIVE:

• Basic functional building blocks of embedded systems

• Register, memory devices, ports, timer, interrupt controllers using circuit

block diagram representation for each categories.

• To understand what is an embedded system.

• To understand the categories and specifications of embedded system.

• To learn the recent trends in embedded system development.

• To learn the hardware and software architecture of an embedded system.

• To gain knowledge about the process of creating an executable image for the

embedded system and the cross platform development.

INTRODUCTION

• An embedded system is a computer system designed to do one or a few

dedicated and/or specific function often with real-time computing constraints.

It is embedded as part of a complete 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.

• An embedded system can be part of a larger system.

• Embedded system is used in any application or device which requires having

certain level of automation or intelligence.

• Embedded systems are controlled by a main processing core that is either a

microcontroller or digital signal processor.

• In addition to commonly described embedded systems based on small

computers, a new class of miniature wireless devices called motes is quickly

gaining popularity as the field of wireless sensor networking rises. These

motes are completely self-contained, and will typically run off a battery

source for many years before the batteries need to be changed or charged.

HISTORY OF EMBEDDED SYSTEM:

• In 1930-40s, Computer were comparable large and expensive, beside, they

were dedicated to a single task only.

• Apollo Guidance Computer (AGC) was first recognizable modern embedded

system developed by Charles Strak Draper, but it was very huge and risk for

Apollo project.

• Charles developed monolithic integrated circuit in order to reduce the size and

weight of AGC.

• In 1961, automatic D-17 guidance computer, were the early mass

produce embedded

• System built from transistor logic and had a hard disk for main memory.

• In 1966, new computer emerged with the first high-volume use of Integrated

Circuits.

• Nowadays, the embedded system finds its application in the fields shown in

the figure 1.

Figure 1: Applications of Embedded system

SYSTEM:

A system is a way of working, organizing or doing one or many tasks

according to a fixed plan, program, or set of rules.

A system is also an arrangement in which all its units assemble and work

together according to the plan or program.

Ex: time- display system, Washing machine.

EMBEDDED SYSTEM:

Components:

1. Microprocessor

2. Memory

3. Input units

4. Output units

5. Networking units

6. I/O units

Main Components:

1. Hardware

2. Software

3. RTOS(Real time operating System)

DEFINITIONS:

An Embedded system is a system whose principal function is not

computational, but which is controlled by a computer embedded with in it. The

world embedded implies that it lies inside the overall system, hidden from view,

forming an integrals part of greater whole.

Or

An Embedded system is a micro-controller based, software-driven, reliable,

real time control system, autonomous, or human- or network – interactive, operating

on diverse physical variables and in diverse environments, and sold into a

competitive and cost-conscious market.

Classifications:

1. Small Scale Embedded systems

2. Medium Scale Embedded systems

3. Sophisticated Embedded systems

CATEGORIES OF EMBEDDED SYSTEMS :

• Based on functionality and performance requirements, embedded systems can

be categorized as:

• Stand-alone embedded systems

• Real time systems

• Networked information appliances

• Mobile devices

STAND ALONE EMBEDDED SYSTEMS

• These systems work in stand-alone mode.

• They take inputs, process them and produce the desired output.

• The input can be electrical signals from transducers or commands from

a human being such as the pressing of a button.

• The output can be electrical signals to drive another system, an LED display

or LCD display for displaying of information to the users.

Examples:

Embedded systems used in

• process control,

• automobiles,

• Consumer electronic items etc.

REAL TIME SYSTEMS

Embedded systems in which some specific work has to be done in a specific

time period are called real time systems.

Types of real time systems:

a. Hard real time systems: missing a deadline may lead to a

catastrophe. e.g.: DVD player

b. Soft real time systems: the deadline is important but missing the deadline

will not lead to a catastrophe.

E.g.: missile embedded with a tracking system

SPECIFICATIONS OF EMBEDDED SYSTEMS :

1. SAFETY AND RELIABILITY:

• Embedded systems must be very reliable as they perform critical functions.

• In mission- critical applications such as aircraft flight control, severe personal

injury or equipment damage could result from the failure of embedded

computer.

• Hence embedded system programmers should take into considerations all

possibilities and write programs that do not fail.

2. PERFORMANCE:

Many embedded systems have time constraints.

Eg:

• For instance, in a process control system, a constraint can be : “if the

temperature exceeds 40 degrees, open a valve within 10 milliseconds”.

• The system must meet such deadlines.

• If the deadlines are missed, it may result in a catastrophe. You can imagine the

damage that can be done if such deadlines are not met in a safety system of a

nuclear plant.

3. POWER CONSUMPTION:

• Most of the embedded systems operate through a battery.

• To reduce the battery drain and to avoid frequent recharging of the battery, the

power consumption of the embedded system has to be very low. The number

of hardware components should also be reduced.

• To reduce power consumption, the hardware designers have the option of

using PLDs and FPGAs.

• Reducing the component count apart from reducing the power consumption

also increases the reliability of the system.

4. COST:

• For embedded systems used in safety applications of a nuclear plant or in a

spacecraft, cost may not be a very important factor.

• Embedded systems used in consumer electronics or office automation, the

cost is utmost important.

5. ROBUSTNESS:

• Embedded systems must robust as they operate in harsh environment. They

should endure vibrations, power supply fluctuations and excessive heat.

6. SIZE:

• The size and the weight are important parameters in embedded systems used

in aircraft, spacecraft, missiles etc. because in such cases, every inch and

every gram matters.

• To reduce the size and the weight, again the hardware engineers have to

design their boards by reducing the component count to the maximum

possible extent.

• The development in microelectronics has reduced the size and the weight of

the embedded system devices to a very great extent.

7. LIMITED USER INTERFACE:

• Some embedded systems do not have any user interface at all. They take

electrical signals as input and produce electrical signals as output.

• In many embedded systems, the input is through a small function keypad or a

set of buttons. The output is displayed either on a set of LEDs or a small LCD.

• Developing a user friendly interface with limitation of the input/output

devices is a challenging task for firmware developers.

8. SOFTWARE UPGRADATION CAPABILITY:

Embedded systems are meant for a very specific task. So, once the software is

transferred to the system, the same will run throughout its life.But, in some cases, it

may be necessary to upgrade the software.

Eg.: The tariff change in the PCO makes the necessity of changing the program for

calculating the amount of a call. So, it is easier to update the software instead of

replacing the memory chip of thousands of PCOs.

RECENT TRENDS IN EMBEDDED SYSTEMS:

In good old days, most of the embedded software was written only in assembly

language and hence writing, debugging and maintaining the code were very difficult

and time consuming. With the availability of powerful processors and advanced

development tools, embedded software is also developed.

1. PROCESSOR POWER:

• About 150 varieties of processors are available from around 50

semiconductor vendors.

• Powerful 8-bit, 16-bit, 32-bit and 64-bit micro-controllers and

microprocessors are available for real-time analysis of audio and video

signals.

• As a result, the power of desktop computers is now available on palmtops.

2. MEMORY:

• The cost of memory chips is reducing day by day. As a result, the embedded

systems can be made functionally rich by incorporating additional features

such as networking protocols and even graphical user interfaces.

• As the memory chips are becoming cheaper, porting an operating system is no

longer an issue.

• Now, wristwatches with embedded Linux operating system are available.

3. OPERATING SYSTEMS:

• The main advantage of embedding an operating system is that the software

development will be very fast and maintaining the code is very easy.

• The software can be developed in a high-level language such as C. So, time to

market, the system gets reduced.

• If real-time performance is required, a real-time operating system can be

used.

• In addition to many commercial embedded/real-time operating systems, open

source software campaign led to development of many open source operating

systems.

• The attraction of open source software is that it is a free and also the complete

source code is available to customize the software as per your application

needs.

4. COMMUNICATION INTERFACES AND NETWORKING CAPABILITY:

Network-enabling of an embedded system has many advantages:

• It can be accessed over a network for remote control or monitoring

uploaded through the network interface.

• Due to the enhanced memory capacities of the embedded systems, TCP/IP

protocol stack and the HTTP server software can also be ported onto the

system and such systems can be accessed over the Internet from anywhere on

the earth.

5. PROGRAMMING LANGUAGES:

• Due to the availability of cross-compilers, most of the development is now

done in high level languages such as C.

• The object-oriented languages like C++ and java are now catching up.

• Many exciting applications are possible by having a Java Virtual machine in

an embedded system.

6. DEVELOPMENT TOOLS:

• Availability of a number of tools for development, debugging and testing as

well as for modeling the embedded system is now paving way for fast

development of robust and reliable systems.

• Development tools such as MATLAB and Simulink can be used to model an

embedded system as well as to generate code, substantially reducing the

development time.

• Development tools such as BREW(binary Runtime Environment for

Wireless), Java 2 Micro Edition(J2ME) development tools, Wireless

Application Protocol(WAP) development tools facilitate easy development of

applications for mobile devices.

7. PROGRAMMABLE HARDWARE:

• PLDs and FPGAs pave the way for reducing the components on an embedded

system, leading to small, low-cost systems.

• After developing the prototype of an embedded system, for mass production,

an FPGA can be developed which will have all the functionality of the

processor, peripherals as well as the application-specific circuitry.

Keyword: System-On-Chip (SOC) is the catchword that reflects the

current developments in programmable hardware-a single chip is the

embedded system.

HARDWARE ARCHITECTURE:

Some of the building blocks of embedded system hardware are

• Central Processing Unit

• Memory

• Clock circuitry

• Watchdog Timer/Reset circuitry

• Chip select

• Input/output devices

• Debug port

• Communication Interfaces

CENTRAL PROCESSING UNIT:

• The Central Processing Unit (CPU) is the portion of a computer system that

carries out the instructions of a computer program and is the primary element

carrying out the functions of the computer or other processing device.

• The Central Processing Unit carries out each instruction of the program in

sequence, to perform the basic arithmetical, logical, and input/output

operations of the system.

• The CPU used in an embedded system can be of two categories:

• General Purpose Processor (GPP)

• Digital Signal Processor (DSP)

The GPPs are further classified as micro-controllers and microprocessors.

• A microcontroller has memory and other peripherals on the chip itself and

hence it is the best choice for small embedded systems.

• A microprocessor is more powerful but requires a large number of external

components. The CPU consists of the units shown in the figure 3.

Figure 3: Internal architecture of a processor

Arithmetic Logic Unit (ALU) :

This unit performs arithmetic and logic operations such as addition,

subtraction, multiplication etc.

General purpose registers:

• These registers constitute the processor’s internal memory.

• The number of registers varies from processor to processor.

• These registers contain the current data and operands that are being

manipulated by the processor.

Control Unit:

It fetches the instructions from memory, decodes them and

executes them. A control unit consists of

• Instruction Pointer (IP) that points to the next instruction to be

executed. Instruction Pointer is also called Program Counter (PC).

• Stack Pointer (SP) that points to the stack in the memory.

• Instruction Decoder that decodes the instructions.

• Memory Address Register and Memory Data Register.

PROCESSOR ARCHITECTURES:

In addition to manipulating data, a processor’s job is to read data and

instructions from memory, read and write data to memory, write data to output

devices and read data from input devices.

To do these functions, the processor communicates with other devices using three

buses, a bus being a group of signals.

These buses are:

Data bus : which carries the data between the processor and other devices. This bus

is bi-directional.

Address bus : which carries the address information from the processor to memory

and hence this bus is unidirectional.

Control and Status bus : which carries control/status information such as whether the

operation is read or write, indication of address error as well as processor reset

signal, clock input and interrupt signals. This bus is bi-directional.

Based on the number of memory and data buses used, there are three types of

architectures for the processors. These are:

• Von Neumann architecture

• Harvard architecture

• Super Harvard architecture

Von Neumann Architecture:

It is the most widely used architecture. It has one memory chip which stores

both instructions and data. The processor interfaces with the memory through

address and data buses to fetch instructions and data. Figure 4 shows the Von

Neumann architecture.

Figure 4: Von Neumann Architecture

Harvard Architecture :

In this architecture , there are two separate memory blocks:

• Program memory

• Data memory

Program memory stores only instructions and data memory stores only data.

Two pairs of data buses are used between the CPU and the memory blocks.

• This architecture is much more efficient because accessing the instructions

and data will be very fast.

• The figure 5 shows the Harvard architecture.

Figure 5: Harvard Architecture

MEMORY:

Types:

Two categories:

1. Program memory

2. Data memory

The program memory stores the firmware permanently whereas data memory

contents are erased when power is switched off.Both program memory and data

memory can be internal to the processor (as in the case of a microcontroller) or it can

be external memory.

In a micro-controller, both program memory and data memory are on chip.

However, if the capacity of the internal memory is not sufficient, you can use

external memory chips to increase the memory capacity.

Classification of memory chips:

• Random Access Memory (RAM)

• Read-Only Memory (ROM)

• Hybrid Memory

Random Access memory (RAM)

• The memory locations can be accessed randomly.

• RAM is a read-write chip as you can perform both read and write operations

on it.

Types:

1. Static RAM (SRAM) : It loses contents the moment power is switched off to

the chip. Faster and consumes less power.

2. Dynamic RAM (DRAM) : It retains its contents for a fraction of a second

even if power is supplied continuously to the chip.

3. DRAM has to be refreshed periodically. Cheaper and is used in handheld

computers.

Read Only Memory (ROM)

ROM is used to store the firmware in embedded systems because it retains its

contents even if power is switched off.

Types:

• Programmable ROM (ROM) : Can be programmed only once.

• Erasable Programmable ROM(EPROM): Can be programmed many times.

The contents can be erased using Ultra Violet (UV)radiation.Slower than RAM and

ROMs.

Hybrid Memory devices:

Electrically Erasable PROM (EEPROM) :

EEPROM is similar to EPROM but its contents can be erased by applying

electrical signal to one of the pins of the device.Non-Volatile RAM : Non-Volatile

RAM is SRAM with a battery backup. So, even if power is switched off, the battery

will ensure that the contents are not erased.

Flash Memory:

It is a type of EEPROM. The memory is divided into sectors or blocks.

Typical sector size is 256 bytes to 16KB. Each sector is an erasable unit.

Flash memory is nowadays extensively used in embedded systems for storing

the firmware.

PORTS

Serial means one event at a time. It is usually contrasted with parallel,

meaning more than one event happening at a time. In data transmission, the

techniques of time division and space division are used, where time separates the

transmission of individual bits of information sent serially and space (on multiple

lines or paths) can be used to have multiple bits sent in parallel. In the context of

computer hardware and data transmission, serial connection, operation, and media

usually indicate a simpler, slower operation and parallel indicates a faster operation.

This indication doesn't always hold since a serial medium (for example, fiber optic

cable) can be much faster than a slower medium that carries multiple signals in

parallel.

On your PC, the printer is usually attached through a parallel interface and

cable so that it will print faster. Your keyboard and mouse are one-way devices that

only require a serial interface and line. Inside your computer, much of its circuitry

supports bits being moved around in parallel. The computer modem uses one of your

PC's serial connections or COM ports. Serial communication between your PC and

the modem and other serial devices adheres to the RS-232C standard. Conventional

computers and their programs operate in a serial manner, with the computer reading

a program and performing its instructions one after the other. However, some of

today's computers have multiple processors and can perform instructions in parallel.

In the context of computer hardware and data transmission, serial connection,

operation, and media usually indicate a simpler, slower operation. Parallel

connection and operation indicates faster operation. A conventional phone

connection is generally thought of as a serial line since its usual transmission

protocol is serial. Conventional computers and their programs operate in a serial

manner, with the computer reading a program and performing its instructions one

after the other. However, some of today's computers have multiple processors that

divide up the instructions and perform them in parallel.

USB (Universal Serial Bus) is a "plug-and-play" interface between a computer

and add-on devices (such as audio players, joysticks, keyboards, telephones,

scanners, and printers). With USB, a new device can be added to your computer

without having to add an adapter card or even having to turn the computer off. The

USB peripheral bus standard was developed by Compaq, IBM, DEC, Intel,

Microsoft, NEC, and Northern Telecom and the technology is available without

charge for all computer and device vendors.

USB supports a data speed of 12 megabits per second. This speed will

accommodate a wide range of devices, including MPEG-2 video devices, data

gloves, and digitizers. It is anticipated that USB will easily accommodate plug-in

telephones that use ISDN and digital PBXs. Since October, 1996, the Windows

operating systems have been equipped with USB drivers or special software

designed to work with specific I/O device types. USB is integrated into Windows

98. As of mid-1998, most new computers and peripheral devices were equipped with

USB.

FireWire is Apple Computer's version of a new standard, IEEE 1394 High

Performance Serial Bus, for connecting devices to your personal computer. FireWire

provides a single plug-and-socket connection on which up to 63 devices can be

attached with data transfer speeds up to 400 Mbps (megabits per second). The

standard describes a serial bus or pathway between one or more peripheral devices

and your computer's microprocessor. In the next few years, you can expect to see

many peripheral devices coming equipped to meet this new standard. FireWire and

other IEEE 1394 implementations provide:

• A simple common plug-in serial connector on the back of your computer and

on many different types of peripheral devices

• A thin serial cable rather than the thicker parallel cable you now use to your

printer, for example

• A very high-speed rate of data transfer that will accommodate multimedia

applications (100 and 200 megabits per second today; with much higher rates

later)

• Hot-plug and plug-and-play capability without disrupting your computer

• The ability to chain devices together in a number of different ways without

terminators or complicated set-up requirements

In time, IEEE 1394 implementations are expected to replace and consolidate

today's serial and parallel interfaces, including Centronic parallel, RS232-C, and

SCSI. The first products to be introduced with FireWire include digital cameras,

digital video disks (DVD), digital video tapes, digital camcorders, and music

systems. Because IEEE 1394 is a peer-to-peer interface, one camcorder can dub to

another without being plugged into a computer. With a computer equipped with the

socket and bus capability, any device (for example, a video camera) can be plugged

in while the computer is running.

There are two levels of interface in IEEE 1394, one for the backplane bus within

the computer and another for the point-to-point interface between device and

computer on the serial cable. A simple bridge connects the two environments. The

backplane bus supports 12.5, 25, or 50 megabits per second data transfer. The cable

interface supports 100, 200, or 400 megabits per second. Each of these interfaces can

handle any of the possible data rates and change from one to another as needed.

The serial bus functions as though devices were in slots within the computer

sharing a common memory space. A 64-bit device address allows a great deal of

flexibility in configuring devices in chains and trees from a single socket. IEEE 1394

provides two types of data transfer: asynchronous and isochronous. Asynchronous is

for traditional load-and-store applications where data transfer can be initiated and an

application interrupted as a given length of data arrives in a buffer. Isochronous data

transfer ensures that data flows at a pre-set rate so that an application can handle it in

a timed way. For multimedia applications, this kind of data transfer reduces the need

for buffering and helps ensure a continuous presentation for the viewer. The 1394

standard requires that a device be within 4.5 meters of the bus socket. Up to 16

devices can be connected in a single chain, each with the 4.5 meter maximum

(before signal attenuation begins to occur) so theoretically you could have a device

as far away as 72 meters from the computer.

TIMERS:

• 8 Bit wide.

• Clocked internally by system clock which is Fosc/4 or by external clock on

RA4/TOCKI.( Frequency 0 –50 MHz)

• Incrementing. Overflows from FF-00 and generates interrupt.

• 2 cycle delay after prescalerfor purpose of synchronization of external with

internal clock.

• Timer0 delay= { [Timer0 count] x PrescalerValue x 4/Fosc}

• Timer0 preload = 256 –[ Timer 0 delay x Fosc]/ Prescalevalue x 4]

Watchdog Timer/ Reset circuitry:

• Due to some software or hardware error, a need may arise to reset

the processor. Most of the embedded systems do not have a reset

button.

• The watchdog timer does the resetting.

• A timer is set to a large value and it is decremented slowly.

• If the timer value reaches zore, the processor is reset through a reset-

signal.

• If a reset button is provided in an embedded system, on pressing the

button, a reset signal is sent to the processor.

• The processor sends a periodic signal to the reset circuit indicating that it

is healthy.

• If the reset circuitry does not receive this signal, then the processor is

reset.

INTERRUPTS:

• Interrupt is a signal to the processor that some important event has occurred.

Example:The processor does not keep on checking whether you are pressing a

key on thekeyboard.

• Whenever a key is pressed, an interrupt goes to the processor and then the

processorreads the key pressed.

• There will be an Interrupt Service Routine (ISR) that will be executed.But,

before executing the ISR, the processor has to temporarily halt the work it is

doing.So, it saves the contents of the registers by pushing the register values

and stack pointeronto the stack.

• Then the processor loads the interrupt vector, i.e. the address at which the ISR

is lying ,into the program counter.

• After execution of the ISR, the processor reloads the registers and the stack

pointer andresumes the previous execution.

• There may be more than one interrupt to the processor.

• Hence, priorities are assigned to the interrupts so that the processor executes

the highestpriority interrupt.

Type of interrupts:

• NMI (Non-Maskable Interrupt) – interrupt that has to be processed

immediately.

An interrupt table contains the details of various interrupts such as interrupt

number (IRQ), the memory location where the ISR is stored (interrupt vector),

priority of the interrupt and the frequency with which the interrupt is likely to occur.

CISC and RISC:

Processors are divided into the following categories:

• CISC (Complex Instruction Set Computer)

• RISC (Reduced instruction Set Computer)

Summary:

Ø System:

A way of working, organizing or doing some task or series of tasks by following

fixed plan , program and set of rules

Ø Embedded system:

A sophisticated system that has a computer as one of its components. An

embedded system is a dedicated computer based system for an application or

product

Ø Processor:

A Processor implements a process or processes as per the command.

Ø Process:

A program or task or thread that has a distinct memory allocation of its own and

has one or more functions or procedures for specific job. The process may share

the memory with other tasks. A processor may run multiple processes separately

or concurrently

Ø Micro controller:

A unit with a processor. Memory , timers , watch dog timer , interrupt controller ,

ADC or PWM etc are provided as required by the application.

Ø GPP:(General Purpose Processor)

A Processor from a number of families of processors, micro controllers ,

embedded processors and digital signal processors having a general purpose

instruction set readily available compilers to enable programming in a high level

language

Ø ASSP: (Application Specific system processor)

A processing unit for specific tasks , for example image compression , and that is

integrated through the busses with the main processor in the embedded system

Ø ASIP:( Application specific Instruction processor)

A Processor designed for specific application on a VLSI chip

Ø FPGA:

These are Field programmable gate arrays on a chip. The chip has a large number

of arrays with each element having fusable links. Each element of array consists

of several XOR,AND,OR , multiplexer , demultiplexer and tristate gates.

Ø Registers:

These are associated with the processor and temporarily store the variable values

from the memory and from the execution unit during processing of an instruction.

Ø Clock:

Fixed frequency pulses that an oscillator circuit generates and that controls all

operations during processing and all timing references of the system. Frequency

depends on the needs of the processor unit. A processor if it needs 100MHz clock

then its minimum instruction processing time is reciprocal of it, which is 10 ns.

Ø Reset:

A processor state in which the processor registers acquire initial values and from

which starts an initial program ; this program is usually the one that also runs on

power up.

Ø Reset circuit:

A circuit to force reset state and that gets activated for a short period on power

up. When reset is activated, the processor generates reset signal for the other

system units needing reset.

Ø Memory:

This stores all the programs , input data and output data. The processor fetches

instructions from it to execute and gives the processed results back to it as per the

instruction.

Ø ROM:

A read only memory that locates the following in its ROM- embedded software ,

initial data and strings and operating system or RTOS.

Ø RAM:

This is a Random Access Read and Write memory that the processor uses to store

programs and data that are volatile and which disappear on power down or off.

Ø Cache:

A Fast read and write on-chip unit for the processor execution unit. It stores a

copy of a page of instructions and data. It has these fetched in advance from the

ROM and RAM so that the processor does not have to wait for instruction and

data from external buses.

Ø Timer:

A unit to provide the time for the system clock and real time opertions and

scheduling.

Ø Watch dog timer:

A timer the timeout from which resets the processor in case the program gets

struck for an unexpected time.

Ø Interrupt controller:

A unit that controls the processor operations arising out of an interrupt from a

source.

Ø ADC:

A unit that converts, as required , the analog input between + and – pins with

respect to the reference voltage to digital 8 or 10 or 12 bits.

Ø PWM:

Pulse width modulator to provide a pulse of width scaled to the analog output

desired. On integrating PWM output , the DAC operation is achieved.

Ø DAC:

Digital bits ( 8 or 10 or 12) converted to analog signal scaled to a reference

voltage

Ø Device driver:

Interrupt service routine software , which runs after the programming of the

control register of a peripheral device and to let the device get the inputs or

outputs. It executes on an interrupt to or from the device.

Ø Device manager:

Software to manage multiple devices and drivers.

Ø Multitasking:

Processing codes for the different tasks as directed by the scheduler.

Ø Real-time operating system:

Operating system software for real-time programming and scheduling , process

and memory manager , device drivers , device management and multi tasking.

Ø VLSI chip:

A very large scale integrated circuit made on silicon with approximately 1

million transistors.

Ø System on chip :

A system on a VLSI chip that has all of needed analog as well as digital circuits,

for example in a mobile phone.

16-MARK QUESTIONS:

1.Explain about the different components present in embedded system hardware.

(P.NO.3)

2.What are the different classifications of embedded systems explain it with neat

diagram. (P.NO.5)

3.Modify the role of processor in the system. (P.NO.7).

4.Differentiate the microprocessor and micro controllers with all its functional areas.

(P.NO. 9).

5.How can you design an embedded processor for a complex system? (P.NO. 11).

6.Write the notes on DSP, ASSPs and GPP. (P.NO.13).

7.Illustrate the other hardware units present in an embedded system. (P.NO. 15).

8.Give the correct procedure for embedding the software into a system. (P.NO. 28).

9.What are the applications of embedded systems in various areas? (P.NO. 37).

10.Implement the embedded system on a single chip (SOC) and in VLSI circuit.

(P.NO.39).

TEXT BOOK : Embedded Systems by Raj Kamal.

TWO MARK QUESTIONS:

1.Define system.

A system is a way of working, organizing or doing one or many tasks

according to a fixed plan, program or set of rules.

2.What are all the components present in embedded system?

The components present in embedded system are microprocessor, memory

unit, input units, output units, networking units and I/O units.

3.When will be microprocessor used?

A microprocessor is used when large embedded software is to be located in

the external memory chips. RISC core microprocessor is used when intensive

computations are to be performed.

4.Where we are using the micro controller?

A Micro controller is used when a small or part of the embedded software has

to be located in internal memory and when the on chip functional units like interrupt

handler, port, timer, ADC and PWM are needed.

5.What is the need of ASSP?

An ASSP is used as an additional processing unit for running the application

specific tasks in place of processing using embedded software.

6.Write the use of multiple processors.

Multiple processors are used when a single processor does not meet the needs

of the different tasks that have to be performed concurrently. The operations of all

the processors are synchronized to obtain an optimum performance.

7. What are the four operation ranges of power supply in the embedded system?

The four operation ranges of power supply in the embedded system are

5 V ± .25 V

3.3V ± .3 V

2 V ± .2 V

1. 5 V ± .2 V

8.Write the use of clock oscillator in a embedded system.

It controls the various clocking requirements of the CPU, of the system timers

and the CPU machine cycles.

9.What is the need of CPU machine cycles?

The machine cycles are for

Fetching the codes and data from memory and executing at the processor

Transferring the results to memory.

10.Define GPP.

It is a General Purpose Processor. A Processor from a number of families of

processors, micro controllers, embedded processors and DSPs having a general

purpose instruction set and readily available compilers to enable programming in a

high level language.

11. Write short notes on ASIP.

It is Application Specific Instruction Processor. A processor designed for a

specific application on a VLSI chip.

12.What is mean by FPGA?

These are Field Programmable Gate Arrays on a chip. The chip has a large

number of arrays with each element having fusable links. Each element of array

consists of several XOR, AND, OR, multiplexer, demultiplexer and tristategates.

13.Define registers.

`These are associated with the processor and temporarily store the variable

values from the memory and from the execution unit during processing of an

instructions.

14.What is mean by cache?

A fast read and write on a chip unit for the processor execution unit. It stores a

copy of a page of instructions and data. It has these fetched in advance from the

ROM and RAM so that the processor does not have to wait for instruction and data

from external buses.

15.What is the use of interrupt controller?

A unit that controlles the processor operations arising out of an interrupt from

the source.

16.Define ADC.

A unit that converts, as required the analog input between + and – pins with

respect to the reference voltage to digital 8 or 10 or 12 bits.

17.Abbreviate the PWM.

Pulse Width Modulator is used to provide a pulse of width scaled to the

analog output desired. On integrating PWM output, the DAC operation is achieved.

18.State the function of LED.

Light Emitting Diode it is a diode that emits red, green, yellow or infrared

light on forward biasing between 1.6V to 2V and currents between 8-15Ma. Multi

segment and multi line LED units are used for bright display of digits, characters,

chart and short messages.

19.Define modem.

A circuit to modulate the outgoing bits into pulses usually used on the

telephone line and to demodulate the incoming pulses into bits for incoming

messages.

20.Define linker.

A program that links the compiled codes with the other codes and provides

the input for a loader or locator.

21.When mask and ROM mask is created?

It is created at a foundary for fabrication of a chip. The ROM mask is reated

from the ROM image file.

22.What is the use of pipe?

A data structure or virtual device which is sent a byte stream from a data

source and delivers the byte stream to the data sink.

23.What is VLSI chip?

It is a very large-scale integrated circuit. It is made on with 1M transistors.

24.What is meant by real time operating system?

Operating system software for real time programming and scheduling, process

and memory manager, device drivers, device management and multitasking.

25.What is SOC?

A system on a VLSI chip that has all of needed analog as well as digital

circuits. Ex…. In a mobile phone.