c1 Intro Student Version

8/6/2019 c1 Intro Student Version

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Embedded Systems

Overview

Phan Duy Hng (PhD)

ES Lecturer Hanoi FPT University


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Content

What is an Embedded System ?

Embedded System Structure

General Characteristics of Embedded Systems

Design Issues

Design Metrics

Essential Considerations

Programming

New trends in ES


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What examples ofembedded systems do you know ?


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Examples

Telecommunication systems

Consumer electronics

Transportations systems

Medical equipment

EmbeddedSystem


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Example 1: The Domestic Fridge

The

Embedded

Computer

An Embedded

System

Compressor Control

Actual Temperature

HumanInteraction

Alarm

Display

Required Temperature

Networked

Interaction

(Maybe!)


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Example 2: Car Door Control, within a LargerNetwork

Dash

Board

irBag

adio

Climate

& CD

Door

Door

teeringDriver's

eat

CentralControl

C N Bus

Control

Le t

ight

open door sensor

window control buttons

lock controllock actuator

window motor

window stall sensor


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PIC

Pulse Width Modulation

Serial Data

SerialMicrocontroller

Compass

Motor Drive

Interface

Stream x2

UltrasoundRanging

Pulse Echo

Motor

ump Sensor

Power

Management

Regulation

9V

Alkaline

5V

9V

Right

ump Sensor

Left

Light Sensor

Left

Light Sensor

Right

Analog to Digital

Converter

Left

Motor

Clock

Module

Serial Extension

us

Light Sensor

Rear UltrasoundServo

Right

Example 3: The Derbot Autonomous Guided Vehicle


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Example 4: Electrocardiograph


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What is an embedded system ?


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An embedded system is a computer system

designed to perform one or a few dedicated

functions often with real-time computing

constraints. It is embedded as part of a complete

device often including hardware and mechanical

parts.

In contrast, a general-purpose computer, such as a

personal computer, is designed to be flexible andto meet a wide range of an end-user s needs.

wiki


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Embedded System Structure

An embedded system is a system whose principal function is not

computational, but which is controlled by a computer embedded within it.

utVa ia les t t

se te ace

Va ia les

i t t e ste s

e e C te

Software

Har ware

Si

al

C

iti

i

ata

C

esi

t

t

i

e

is la e a etc


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uP varieties

uController: includes I/O devices

On-board memory.

Digital signal processor (DSP): Optimized for digital signal processing.

Typical embedded word sizes: 8-bit, 16-bit,

32-bit.


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Characteristics

General Characteristics

Application Specific CharacteristicsDSP Characteristics

Distributed Characteristics


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Design

Design Issues

Design MetricsWhat is Co-design?


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Knowledge ?


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A Mix of Disciplines

Embedded Systems

Electronics

Electric Motors

Computer Architecture

Software Engineering

Integrated CircuitDesign

Digital

AnalogueElectronics

Actuators

Sensors and

Measurements

Control

Engineering

DataCommunications


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Essential Considerations

Real Time Systems

Memory Organization

Instruction Set

Communication/I/O Interfaces Portability ? Low Power ( attery Life)

Software, Tools


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Real time system ?


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a) The Von NeumannWay b) The Harvard Way

Memory Organisation

Data

Memory

Program

Memory

Address

Data

Central

ProcessingUnit (CPU)

Input/Output CentralProcessing

Unit (CPU)

Data

Memory

Input/Output

Program

Memory

Address

Data

Address

Data

Address

Data


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CPU Cache


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AD AA A M

M AAND Aw MO Aw ME O Aw M

A leftShift A rightRotate A leftRotate A rightComplement AClearA

A = A plus 1A = A - 1A = A plus MA = A - MA = A MA = A + MA = A M+A = 2AA = A 2

A = NOTAA = 0

A computer executes instructions in itsArithmetic Logic Unit(ALU), running through a series of

instructions called aprogr m. An ALU can only do a few things, but it can do them very fast. Atypical 8-bit ALU can do the list shown below. A is the Accumulator , a digital register where the

computations actually occur, and M is a location in memory. The ALU in turn forms part of the

Central Processing Unit (CPU).

What can the Computer Actually Do? - Instructions and Instruction Sets


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Any CPU has a set of instructions that it recognises and responds to; all programs are built up in one

way or another from this instruction set. We want computers to execute code as fast as possible, buthow to achieve this aim is not always an obvious matter.

One approach is to build sophisticated CPUs with exotic instruction sets, with an instruction ready

for every foreseeable operation. This leads to the CISC, the Complex Instruction SetComputer. A

CISC has many instructions, and considerable sophistication. Yet the complexity of the design

needed to achieve this tends to lead to slow operation. One characteristic of the CISC approach is

that instructions have different levels of complexity. Simple ones can be expressed in a shortinstruction code, say one byte of data, and execute quickly. Complex ones may need several bytes of

code to define them, and take a long time to execute.

A CISC machine is generally recognised by:

Many instructions (say over one hundred), some with considerablesophistication;

Instruction words are of different length;

Instructions take different lengths of time to execute.

How Instruction Sets are Made: the CISC Machine


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Another approach is to keep the CPU very simple, and have a limited instruction set. This leads tothe RISC approach the Reduced Instruction SetComputer. The instruction set, and hence overall

design, is kept simple. This leads to fast operation. One characteristic of the RISC approach is that

each instruction is contained within a single binary word. That word must hold all information

necessary, including the instruction code itself, as well as any address or data information also

needed. A further characteristic, an outcome of the simplicity of the approach, is that every

instruction normally takes the same amount of time to execute.

How Instruction Sets are Made: the RISC Machine

A RISC machine is generally recognised by:

Few instructions (say well below one hundred),

Each performs a very simple action;

All instructions are single word; All, or almost all instructions take the same length of time to

execute.


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Programming

Language features implemented for a particularplatform

Hardware

Operating system

Libraries

Templates

Excellent for embedded systems work

As always, try to write the clearest, cleanest, mostmaintainable code


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Complexity


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Reliability

Embedded systems often reside in machines that areexpected to run continuously for years without errors, and in

some cases recover by themselves if an error occurs.

Specific reliability issues may include:

The system cannot safely be shut down for repair, or it istoo inaccessible to repair.

The system must be kept running for safety reasons.

Often backups are selected by an operator.

The system will lose large amounts of money when shutdown.


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New trends in ES HW


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New trends in ES SW


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The Microchip PIC Families

Details about the 8-bit PIC Architecture Instructions and data are on separate buses, increasing

speed and overall performance

While fetching an instruction on the program bus, data canbe read or written on the data bus

Data bus is 8-bits wide

Program Memory bus optimized to any widths that fitwithin the design goals of the microcontroller

Wider busses allow more information to be transferredfrom memory to the CPU, enabling many instructions to beexecuted in a single clock cycle

12-bit ( aseline), 14-bit (Midrange) and 16-bit (PIC18)instructions are upward compatible and maximize

processing efficiency


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The Microchip PIC Families

dsPIC PIC24

PIC32


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A Gathering of Microprocessors and Microcontrollers

PIC 16F84A

PIC 16F877

PIC 12F508

Motorola

68HC05B16PIC 16C72

Motorola 68000

features also appear across

all their microcontrollers,and knowledge of one family can lead

with ease to knowledge of another

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