Scotch Road

(1)

Embedded System Design - NTHU EOS Lab 1 Module-1 Embedded Computing

Introduction

Embedded System Introduction

Embedded Systems Characteristics

Embedded System Design Process

Object-Oriented Design

Unified Modeling Language (UML)

Design Example: Model Train Controller

(2)

Embedded System Introduction Embedded Systems Characteristics Embedded Systems Characteristics

Embedded System Design Process Embedded System Design Process

Object

Object - - Oriented Design Oriented Design

Unified Modeling Language (UML) Unified Modeling Language (UML)

Design Example: Model Train Controller

(3)

Definition

Embedded system: any device that

includes a programmable computer but is not itself a general-purpose computer

e.g., PDA, printer, cell phone

e.g., TV, household appliances

e.g., automobiles: engine, brakes, etc

NOT-e.g., PC

(4)

Embedded System Example

CPU

mem input

output analog

analog

embedded

computer

(5)

2-layered System Architecture

THE Application

I/O Manager Graphics

Subsystems Network

Drivers

Device Drivers Scheduler

Graphics Drivers Operating

System Kernel

Hardware

(6)

3-layered System Architecture

Applications

I/O Manager Graphics

Subsystems Network

Drivers

Device Drivers Scheduler

Graphics Drivers Operating

System Kernel

Hardware

Applications

Processes

(7)

Early History (1/2)

Late 1940’s: MIT Whirlwind computer was designed for real-time operations

to control aircraft simulator

First microprocessor: Intel 4004 in early 1970’s

microprocessor: a single-chip CPU

Key breakthrough: HP-35 (1972)

due to the high cost of VLSI design, reuse the HW design by changing the SW

1st handheld calculator to compute complex math functions

HP-35 uses several chips to implement the CPU

(8)

Early History (2/2)

Automobiles used microprocessor-based engine controllers starting in 1970’s.

Control fuel/air mixture, engine timing, etc.

2 pushes: oil crisis & environment protection

low fuel consumption & low emission

Multiple modes of operation: warm-up, cruise, hill climbing, etc.

sophisticated control can only be done with

microprocessors

(9)

Microprocessor Varieties

Microcontroller: includes I/O devices, on- board memory

Players: Intel, ARM, Motorola, Hitachi

Digital signal processor (DSP):

microprocessor optimized for digital signal processing

Players: Analog Devices, Motorola, TI

Typical embedded word sizes: 8-bit, 16-

bit, 32-bit

(10)

Application Examples

Front panel of microwave oven

Advanced thermostat systems

time-temperature settings

Canon EOS 3 has 3 microprocessors

32-bit RISC CPU runs auto-focus and eye-control system

Analog TV: channel selection, etc

Digital TV: audio processing CPU

easier to design & debug

possibility of upgrades

(11)

Automotive Embedded Systems

Today’s high-end automobile may have 100 microprocessors:

4-bit microcontroller checks seat belt

microcontrollers run dashboard devices

16/32-bit microprocessor controls engine

(12)

BMW 850i Brake & Control System

Anti-lock brake system (ABS): pumps brakes to reduce skidding

Automatic stability control (ASC+T):

controls engine to improve stability

ABS and ASC+T communicate

(13)

BMW 850i

brake sensor

brake sensor ABS hydraulic

pump

(14)

Review Slides (1)

Embedded system definition? examples?

First microprocessor?

HP-35 significance?

Microprocessor usage in automobiles?

Microcontroller? DSP?

(15)

Embedded System Introduction

Embedded Systems Characteristics Embedded Systems Characteristics

Embedded System Design Process Embedded System Design Process

Object

Object - - Oriented Design Oriented Design

Unified Modeling Language (UML) Unified Modeling Language (UML)

Design Example: Model Train Controller

(16)

Embedded Systems Characteristics (1/2)

Complex algorithms

e.g., automobile engine control system

Sophisticated user interface

e.g., GPS navigation system

Real-time operation

hard-real-time

e.g. life-critical system

soft-real-time

e.g. GPS navigation system

(17)

Embedded Systems Characteristics (2/2)

Multirate functionality

e.g., multimedia applications (video & audio)

Low manufacturing cost

Low power

excessive power consumption increases system cost

Designed to tight deadlines by small teams

6-month market window is common

e.g. cannot miss back-to-school window for

calculators

(18)

Why use microprocessors?

Alternatives: field-programmable gate arrays (FPGAs), custom logic, etc.

Microprocessors are often very efficient:

can use same logic to perform many different functions

Microprocessors simplify the design of

families of products

(19)

The Performance Paradox

Microprocessors use much more logic to

implement a function than does custom logic

instruction cycle: fetch, decode, execute, write

however, for a set of family functions, microprocessors may use less logic

But microprocessors are often at least as fast:

heavily pipelined

large design teams

aggressive VLSI technology

Microprocessors dominate new fabrication lines

custom logics have to wait and use old VLSI technology

(20)

Power

Custom logic is a clear winner for low power devices

Modern microprocessors offer features to help control power consumption

Software design techniques can help

reduce power consumption

(21)

Embedded System Design Challenges (1/2)

How much hardware do we need?

How big is the CPU? Memory?

more hardware capabilities more money

How do we meet our deadlines?

Faster hardware or cleverer software?

How do we minimize power?

Turn off unnecessary logic? Reduce memory

accesses? run at slower clock rate?

(22)

Embedded System Design Challenges (2/2)

Does it really work?

Is the specification correct?

Does the implementation meet the spec?

How do we test for real-time characteristics?

How do we test on real data?

How do we work on the system?

Observability, controllability?

What is our development platform?

(23)

Review Slides (2-1)

Embedded systems characteristics?

complex algorithms, complicated UI, real-time ops, multi-rate functions, low powers, tight deadline &

budget

FPGA, ASIC, Microprocessor

manufacturing cost, power, efficiency, size, development cost

Microprocessor efficiency factors

pipelined, large design teams, latest VLSI

Embedded system design challenges?

HW usage, efficiency, power, testing, platform

(24)

Review Slides (2-2)

Exec Speed Power Req VLSI Tech Design Team Gate #

Functions Flexibility Manu Cost

Microproc ASIC

FPGA

(25)

Review Slides (2-2)

Fast*

Fast Medium

Exec Speed

Medium*

Low Medium

Power Req

High-end Low-end

Medium

VLSI Tech

Large Medium

Small

Design Team

High Low

Medium

Gate #

More Less

Medium

Functions

High Low

Medium

Flexibility

Expensive Cheap

Medium

Manu Cost

Microproc ASIC

FPGA

(26)

Embedded System Introduction

Embedded Systems Characteristics Embedded System Design Process Embedded System Design Process

Object

Object - - Oriented Design Oriented Design

Unified Modeling Language (UML) Unified Modeling Language (UML)

Design Example: Model Train Controller

(27)

Growth Rate of Embedded Software

1 2

0 10 12 18

months

factor

*) Department of Trade and Industry, London

(1. 4/ ye ar ) [M oo re ’s law ]

>10 times more programmers will write embedded applications than computer software by 2010

Em

be dd ed

so ft wa re

[D TI *]

(~ 2. 5/ yr )

already to-day, more than 98% of all microprocessors are used within

embedded systems

© 2004, reiner@hartenstein.de http://hartenstein.de

(28)

Submarine Programming Model

Hardware invisible:

under the surface

Hardware Algorithm

Assembly Language procedural high level Programming Language Soft ware

This model does not suport Hardware / Configware / Software partitioning

© 2004, reiner@hartenstein.de http://hartenstein.de

(29)

Dominance of the Submarine Model ...

Hardware

... indicates, that our CS education system produces zillions of mentally disabled CS graduates (procedural) structurally

disabled

… disabled to cope with solutions other than instruction-stream-based

© 2004, reiner@hartenstein.de http://hartenstein.de

(30)

Built From Bottom-Up

procedural

have not

You cannot *teach Hardware to a

Programmer

*) efficiently

But to a Hardware Guy you always can teach

Programming

structural

have _natural

© 2004, reiner@hartenstein.de http://hartenstein.de

(31)

Design Methodologies

A procedure for designing a system

Understanding your methodology ensures you didn’t skip anything

Compilers, software engineering tools, computer-aided design (CAD) tools, etc., can be used to:

help automate methodology steps

keep track of the methodology itself

(32)

Design Goals

Performance.

Overall speed, deadlines

Functionality and user interface

Manufacturing cost

Power consumption

Other requirements (physical size, etc.)

(33)

Design Process Abstraction

requirements specification

architecture component

design system integration

top-down design

bottom-up

design

(34)

Top-down vs. Bottom-up

Top-down design:

start from most abstract description

work to most detailed

Bottom-up design:

work from small components to big system

Real design uses both techniques

(35)

Step-1: Requirements

Plain language description of what the user wants and expects to get

May be developed in several ways:

talking directly to customers

talking to marketing representatives

providing prototypes to users for comment

(36)

Sample Requirement Form

name project name

purpose one or 2 sentences inputs type of data? periodic

or non-periodic?

outputs I/O devices?

functions inputs outputs performance real-time req?

manufacturing cost rough estimation

power battery or wall-

powered

physical size/weight e.g., PC or NB?

(37)

Example: GPS moving map requirements

Moving map

obtains position from GPS, paints map from local database.

lat: 40 13 lon: 32 19

I-78

S co tc h R o ad

(38)

Step-1 of GPS moving map (1/3)

Functionality: Show major roads and landmarks for automotive use

User interface: At least 400 x 600 pixel

screen. Three buttons max. Pop-up menu.

Performance: Map should scroll smoothly.

No more than 1 sec power-up. Lock onto GPS within 15 seconds.

Cost: $500 street price = approx. $100

manufacturing cost.

(39)

Step-1 of GPS moving map (2/3)

Physical size/weight: Should fit in hand

Power consumption: Should run for 8

hours on four AA batteries

(40)

Step-1 of GPS moving map (3/3)

name MGPS: GPS moving map

purpose consumer-grade moving map for driving

inputs power button, two control buttons

outputs back-lit LCD 400 X 600 functions 5-receiver GPS; three

resolutions; displays current lat/lon

performance updates screen within 0.25 sec of movement

manufacturing cost $100 cost-of-goods-sold

power 100 mW

physical size/weight no more than 2” X 6”, 12 oz.

(41)

Step-2: Specifications

A more precise description of the system:

should NOT imply a particular architecture

provides input to the architecture design process

Serve as a contract between customers and architects

May include functional and non-functional elements.

May be executable or may be in mathematical

form for proofs

(42)

Step-2 of GPS moving map

Should include:

What is received from GPS

map data

user interface

operations required to satisfy user requests

background operations needed to keep the

system running

(43)

Step-3: Architecture Design

Describe how the system implements the required functions

Specifications: what the system does

Architecture: how the system does things

Hardware components:

CPUs, peripherals, etc.

Software components:

major programs and their operations.

Must take into account functional and non-

functional (cost, speed, etc) specifications

(44)

Step-3: GPS moving map block diagram (1/3)

GPS receiver

search

engine renderer

user interface database

display

(45)

Step-3: GPS moving map Hardware Architecture (2/3)

GPS receiver CPU

panel I/O display frame

buffer

memory

(46)

Step-3: GPS moving map Software Architecture (3/3)

position

database

search renderer

timer user

interface

pixels

(47)

Step-3: Architecture Design (cont)

Functional block diagram first SW/HW architecture

SW HW module mapping

Make sure both functional and non-functional requirements are satisfied

Otherwise, redo Step-3 again

How to make sure non-functional requirements are satisfied?

Experience

Modeling

Simulation

(48)

Step-4: Designing Hardware and Software Components

Must spend time architecting the system before you start coding

Some components are ready-made (e.g.,

CPU, topographic databases), some can

be modified from existing designs, others

must be designed from scratch

(49)

Step-5: System Integration

Put together the components

Many bugs appear only at this stage

Have a plan for integrating components

to uncover bugs quickly, test as much

functionality as early as possible

(50)

Summary

Embedded computers are all around us

Many systems have complex embedded hardware and software

Embedded systems pose many design challenges: design time, deadlines, power, etc.

Design methodologies help us manage the

design process

(51)

Review Slides (3)

Common design goals?

Performance, functionality, user interface, cost, power, size, weight

5-step design process?

Requirements? Requirement form?

Specification?

Architecture design?

Component design?

System integration?

(52)

Embedded System Introduction

Embedded Systems Characteristics Embedded System Design Process

Object

Object - - Oriented Design Oriented Design

Unified Modeling Language (UML) Unified Modeling Language (UML)

Design Example: Model Train Controller

(53)

System Modeling

Need languages to describe systems:

useful across several levels of abstraction;

understandable within and between organizations

Block diagrams are a start, but don’t

cover everything

(54)

Object-Oriented Design

Object-oriented (OO) design: A generalization of object-oriented programming

OO design is different from OO programming

Object = state + methods

State provides each object with its own identity

Methods provide an abstract interface to the

object

(55)

OO implementation in C++

class display {

pixels : pixeltype[IMAX,JMAX];

public:

display() { } // constructor

pixeltype pixel(int i, int j) { return pixels[i,j]; } void set_pixel(pixeltype val, int i, int j)

{ pixels[i,j] = val; }

}

(56)

Objects and Classes

Class: object type

Class defines the object’s state elements

Class defines the methods used to interact with all objects of that type

Each object has its own state (memory)

(57)

OO Design Principles

Some objects will closely correspond to real-world objects

Some objects may be useful only for description or implementation

Not every object is executable

Objects provide interfaces to read/write

state, hiding the object’s implementation

from the rest of the system

(58)

Embedded System Introduction

Embedded Systems Characteristics Embedded System Design Process Object-Oriented Design

Unified Modeling Language (UML) Unified Modeling Language (UML)

Design Example: Model Train Controller

(59)

UML

Developed by Booch et al.

Goals:

object-oriented

visual

useful at many levels of abstraction

usable for all aspects of design

(60)

UML object

d1: Display

pixels: array[] of pixels elements

menu_items pixels is a

2-D array

comment

object name

class name

attributes

(61)

UML class

Display pixels elements menu_items

mouse_click()

draw_box() operations

class name

(62)

The class interface

The operations provide the abstract interface between the class’s

implementation and other classes

Operations may have arguments, return values

An operation can examine and/or modify

the object’s state

(63)

Class Derivation

May want to define one class in terms of another

Derived class inherits attributes, operations of base class

Derived_class

Base_class

UML

generalization

(64)

Class Derivation Example

Display pixels elements menu_items pixel()

set_pixel()

mouse_click() draw_box

BW_display Color_map_display

base class

derived class

(65)

Multiple Inheritance

Speaker Display

Multimedia_display base classes

derived class

(66)

Links and Associations

Link: describes relationships between objects

Association: describes relationship

between classes

(67)

Association Example

message

msg: ADPCM_stream length : integer

message set count : integer

0..* 1

contains

# contained messages # containing message sets

0 or more messages

(68)

Link Example

Link defines the contains relationship:

m1:message msg = msg1 length = 1102 m2:message msg = msg2 length = 2114

ms1:message set

count = 2

(69)

State Machines

a b

state state name

transition

(70)

Event-Driven State Machines

Behavioral descriptions are written as event-driven state machines

Machine changes state when receiving an input

An event may come from inside or

outside of the system

(71)

Event Type

Signal: asynchronous event

Call: synchronized communication

Timer: activated by time

(72)

Signal Event

<<signal>>

mouse_click

leftorright: button x, y: position

declaration

a

b mouse_click(x,y,button)

event description

(73)

Call Event (Procedural Call)

c d

draw_box(10,5,3,2,blue)

(74)

Timer Event

e f

tm(time-value)

• State change after a certain amount of time

• time-value = amount of time to expire

(75)

Example State Diagram

region found

got menu item

called menu item

found object

object highlighted start

finish

mouse_click(x,y,button)/

find_region(region)

input/output

region = menu/

which_menu(i) call_menu(i)

region = drawing/

find_object(objid) highlight(objid)

(76)

Sequence Diagram

Shows sequence of operations over time

Relates behaviors of multiple objects

(77)

Sequence Diagram Example

m: Mouse d1: Display u: Menu

mouse_click(x,y,button)

which_menu(x,y,i)

call_menu(i)

time

lifeline

(78)

Summary

Object-oriented design helps us organize a design

UML is a transportable system design language

Provides structural and behavioral

description primitives

(79)

Embedded System Introduction

Embedded Systems Characteristics Embedded System Design Process Object-Oriented Design

Unified Modeling Language (UML)

Design Example: Model Train Controller

(80)

Model train setup

console

power supply

rcvr motor

ECC address

header command

(81)

Step-1: Requirements (1/2)

Console can control 8 trains on 1 track

Throttle has at least 63 levels

Inertia control adjusts responsiveness with at least 8 levels (加速度)

Emergency stop button

Error detection scheme on messages

(82)

Step-1: Requirements Form (2/2)

name model train controller

purpose control speed of <= 8 model trains inputs throttle, inertia, emergency stop,

train #

outputs train control signals

functions set engine speed w. inertia;

emergency stop

performance can update train speed at least 10 times/sec

manufacturing cost $50

power wall powered

physical size/weight

console comfortable for 2 hands; < 2

lbs.

(83)

Step-2: Conceptual Specification

Before we create a detailed specification, we will make an initial, simplified

specification

Gives us practice in specification and UML.

Good idea in general to identify potential

problems before investing too much effort in

detail

(84)

Basic System Commands

command name parameters

set-speed speed

(positive/negative) set-inertia inertia-value (non-

negative)

estop none

(85)

UML Sequence Diagram

:console :train_rcvr

set-inertia set-speed

set-speed

estop

(86)

Class Diagram

command

set-inertia

value: unsigned- integer set-speed

value: integer

estop

(87)

Subsystem Collaboration Diagram

Shows relationship between console and receiver (ignores role of track):

One console can control up to 8 receivers

:console :receiver

1..n: command

(88)

System Structure Modeling

Some classes define non-computer components

Denote by *name

Choose important systems at this point to

show basic relationships

(89)

Major Subsystem Roles

Console:

read state of front panel

format messages

transmit messages

Train:

receive message

interpret message

control the train

(90)

Console System Class Diagram

console

panel formatter transmitter

Knobs* sender*

1 1

1 1 1

1 1 1 1

1

(91)

Console class roles

panel: describes analog knobs and interface hardware

formatter: turns knob settings into bit streams

transmitter: sends data on track

(92)

Train System Class Diagram

train set

train receiver

controller

motor interface

detector* pulser*

1 1..t

1

1 1 1 1 1

1 1

(93)

Train class roles

receiver: digitizes signal from track

controller: interprets received commands and makes control decisions

motor interface: generates signals

required by motor

(94)

Detailed Specification

We can now fill in the details of the conceptual specification:

more classes

behaviors

Sketching out the spec first helps us

understand the basic relationships in the

system

(95)

Console Physical Object Classes

knobs*

train-knob: integer speed-knob: integer

inertia-knob: unsigned- integer emergency-stop: boolean

pulser*

pulse-width: unsigned- integer direction: boolean

sender*

send-bit()

detector*

read-bit() : integer

(96)

Panel and Motor Interface Classes

panel

train-number() : integer speed() : integer

inertia() : integer estop() : boolean new-settings()

motor-interface

speed: integer

(97)

Class Descriptions

panel class defines the controls

new-settings() behavior reads the controls

motor-interface class defines the motor

speed held as state

(98)

Transmitter and Receiver Classes

transmitter

send-speed(adrs: integer, speed: integer)

send-inertia(adrs: integer, val: integer)

set-estop(adrs: integer)

receiver

current: command new: boolean

read-cmd()

new-cmd() : boolean rcv-type(msg-type:

command)

rcv-speed(val: integer)

rcv-inertia(val:integer)

(99)

Class Descriptions

transmitter class has one behavior for each type of message sent

receiver function provides methods to:

detect a new message

determine its type

read its parameters (estop has no parameters)

(100)

Formatter Class

formatter

current-train: integer

current-speed[ntrains]: integer current-inertia[ntrains]:

unsigned-integer

current-estop[ntrains]: boolean send-command()

panel-active() : boolean

update-panel()

(101)

Formatter Class Description

Formatter class holds state for each train, setting for current train

The operate() operation performs the

basic formatting task

(102)

Control Input Cases

Use a soft panel to show current panel settings for each train

Changing train number:

must change soft panel settings to reflect current train’s speed, etc.

Controlling throttle/inertia/estop:

read panel, check for changes, perform

command

(103)

Control Input Sequence Diagram

:knobs :panel :formatter :transmitter

ch an g e in s p ee d / in er ti a/ es to p ch an g e in tr ai n n u m b er

change in control settings

read panel panel settings

panel-active send-command

send-speed, send-inertia.

send-estop read panel

panel settings read panel panel settings

change in train number

set-knobs

new-settings

(104)

Formatter Operate Behavior

idle

update-panel()

send-command() panel-active() new train number

other

(105)

Panel-active behavior

panel*:read-train()

current-train = train-knob update-screen

changed = true T

panel*:read-speed() current-speed = throttle changed = true

T F

...

F

...

(106)

Controller Class

controller

current-speed: integer

current-inertia: unsigned-integer

set-speed(integer)

set-inertia(integer)

new-speed(integer)

(107)

Setting the Speed

Don’t want to change speed instantaneously

Controller should change speed gradually

by sending several commands

(108)

Set-Speed Sequence Diagram

:receiver :controller :motor-interface :pulser*

new-cmd cmd-type

rcv-speed new-speed set-pulse

set-pulse

(109)

Refined Command Classes

command type: 3-bits address: 3-bits parity: 1-bit

set-inertia type=001 value: 3-bits set-speed

type=010 value: 7-bits

estop

type=000

(110)

Summary

Separate specification and programming

Small mistakes are easier to fix in the spec

Big mistakes in programming cost a lot of time

You can’t completely separate specification and architecture

Make a few tasteful assumptions

(111)

Useful Links

http://www.uml.org/

Official UML resource page

You will find many good links here

http://www.raba.com/~jcstaff/oodev/presents /uml/intro_uml/

A pretty good introduction to UML

http://www.softdocwiz.com/UML.htm

UML Dictionary

http://uml.tutorials.trireme.com/

A relatively complete UML tutorial