SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Introduction to real-time systems - slide 1 Software engineering for real-time systems.

SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Introduction to real-time systems - slide 1

Software engineering for real-time systems

Section 1

Introduction to real-time systems


Objectives

To:

• Outline the differences between general-purpose computer applications and real-time systems.

• Give an overview of practical real-time system structures.

• Describe some key environmental and performance requirements of embedded real-time computers.

• Describe the structures of modern microprocessors and microcomputers.

Introduction


Craysupercom puter

Fibre-opticcom m unication unit

F ibre-opticcom m unication unit

F ibre-opticdata link

Rem ote siteLocal site

A modern batch system


Localm ultiplexer

Site 1

Localm ultiplexer

Site 2

Central(m ainfram e)

com puter

Rem ote site

Typical interactive on-line computer system


Control panel

Controlcom puter

Power unit

Vehiclesensors

A real-time computer system


SLOW FAST

SOFT Machinery condition monitoring Man-Machine Interfacing

HARD Missile point defence system Airbag control system

• Two major categorization factors: criticality and speed.

• Criticality:

• Hard systems - deadlines (responsiveness) is critical. Failure to meet these have severe consequences (e.g. injury, damage or death).

• Soft systems - deadlines are less critical; in many cases significant tolerance can be permitted.

• Speed:

– Fast systems - responses in the microseconds to hundreds of milliseconds.

– Slow systems - responses in the range seconds to days.

– Arbitrary boundary: 1 second (chosen because the problems shift from individual computing issues to overall system behaviour and interaction at around this point).

Categorizing real-time systems


• Major attributes of real-time systems.

• For hard systems emphasis is placed on the need to meet deadlines.

• Hard-fast systems tend to have low software complexity.

• For soft-fast systems emphasis is put on computation performance.

• In general soft systems tend to be the more complex ones (from a software perspective).

Execution

time

Deadlines Software

size

Software

complexity

Hard - Fast

Hard - Slow

Soft - Fast

Soft - Slow

Attribute rating Low high

Attributes of real-time systems


R em ote p lant 1

Data collection

Control functions

Com m unication interface

Microprocessor-based outstation

Sensors

Actuators

Land linecom m unication link

(10 m iles)

W irelesscom m unication link

(100 m iles)

Front-endcom m unication

interface

Main controlcom puter

Hot standbycontrol com puter

Operator displayand controls

Data loggingcom puter

Managem entinform ationcom puter

Local area netw ork

C entra l contro lroom

R em oteplant 2

Telemetry control system


Sea Skua missile system


Submarine control console


Typical avionic platforms


Microprocessor-based vending machine units


Consumer communications


Em bedded system splatform s

Bespoke designsCom m ercial off the shelf

(COTS) equipm ent

Board-baseddesigns

PC-baseddesigns

VMEPC/104

Em bedded PCDesktop

PCRuggedized

PCVendorspecific

Embedded systems platforms


Em bedded system scharacteristics

Defined by

Environm ent Perform ance Interfacing

Physical E lectricial Operational Speed ofresponse

Failurem odes

Embedded systems characteristics


Degrees centigrade

-55 0 +50 +85 +125 +200

Military range

Industrialrange

O il exploration

Space exploration

Extended industrialrange

Typical temperature specifications for real-time systems


Computer loading - single synchronous (periodic) task

Executecontrol task

Spare (idle)time

Tsam

t1t0 t2

Time

Te Ti Te Ti

Te = execution time

Ti = idle (spare) time

Tsam = sample time


E xecu teeven t task

(E )p rocessor id le (I)

T e T e T e

(I)


(E )


(E )

Tim e

(I)

Eventsignal

Eventsignal

Eventsignal

Computer loading - single asynchronous (aperiodic) task


Computer loading - multiple asynchronous (aperiodic) tasks

(I)(E1) (E2)(E1) (E1) (E1) (E2)(I) (I)

S1 S1S1S1

S2

(W)

S2

( W) = waiting time for task tocomplete

(I)

Time

(E1) = Event task 1 execution(E2) = Event task 2 execution(S1) = Event signal, task1(S2) = Event signal, task 2(I) = Idle (spare) time


C om puting e lem ents

M icroprocessors M icrocom puters

S pecia lized com putingG enera l pu rpose com puting

G enera l pu rposem icrop rocessors

H igh ly in teg ra tedm icrop rocessors

S ing le ch ipm icrocom pute rs

S ing le ch ipm icrocon tro lle rs

D ig ita l s igna lp rocessors

(D S P s)

M ixed s igna lp rocessors

B espokesystem -on-ch ip

designs

The computing elements of real-time systems


Elements of a microcomputer system

Microprocessor (CPU)

Program store (non-volatile)EPROM/Flash/FRAM

Data store (volatile)RAM

External bus interface

Address decoder

* Optional elements

Real-time clock

Hardware timers

Interrupt controllers

Watchdog timer

Serial communicationscontroller

DMA controller *

I/O peripheral *Core elements

Additional elements


Timing in hardware

Real-time clock Programmable timer

Addressbus Chip

selectline

Controlbus

Tointerrupt


A ddressdecoder

R e triggerab le tim er(m onostab le )

I/P

O/P

To non-m askab le in te rrup t

E xte rna l a la rm (op tiona l)

W ritecon tro l

A ddressbus

O/P

I/P

T im e

Timeout

The watchdog timer


F ig .1 .21 D M A opera tion

R O M

R A M

D M Acon tro lle r

P eriphera lin te rface

D M Arequest/ack

(B) DMA modeof operation

M icro

R O M

R A M

D M Acon tro lle r

P eriphera lin te rface

P rocessor ho ld /ack

D M Arequest/ack

(a) Normal modeof operation

DMA operation


Intelligent I/O processing

Mainprocessor

I/O processorDisk store

Localmemory

Primarybus

Secondarybus


Programmablecommand

register

Data bus buffer

Address andcontrol interface

I/O port

I/O port

I/O port

8 lines

8 lines

8 lines

Addressand controlbus

Databus

I/O interface peripheral


PowerPC 603em icroprocessor core

(including floating pointm aths unit)

Centralcontrol unit

Data pathcontroller

Mem orycontroller

PCI bus interfaceunit

Interruptcontroller and

tim ers

DMAcontroller

Serialcom m s

controller(I2C)

Intelligentm essagecontroller

(I2O)

PCI busarbiter

Busrequest

(5)

Busgrant

(5)

PCI bus

I2C bus

Databus

Mem orybus

Interrupts

Highly integrated processor -Motorola MPC8240


Processor

Clock

Program store(8kByte ROM)

Data store(256 Bytes RAM)

Hardware tim ers(3)

Interruptcontroller

Serialcom m unication

controller

I/O ports (4)

Security ROM

External bus

Single chip microcomputer - Philips Semiconductor 8052


LED driver

DAC (2)

S tepper m otorcontrol

I2C serialinterface

Sound generator

GP Serial I/O

ADC (16)

Interruptinterface (8)

Real-tim e clock

Hardware tim ers(6)

Pulse generator

D igital I/0

CPU W atchdog Interrupt controller Data RAM (16 kByte) DMA Cache m em ory (1

kByte)

P rocessor un it

Boot ROM (2 kByte)

Businterface

CANinterface

(3)

F lash(512

kByte)

Externalbus

Single chip microcontroller - Fujitsu MB91F361


Digital signal processor structure

Addressgenerator

Program(instruction)

control

DMA

Program ROM

Data ROM

Data RAM

Cache

Register unit

Arithmetic-logic unit

(ALU)

Multiplier

Shifter

Serial interface

Bus interface

External bus


Flash(256 bytes)

RAM(256 bytes)

CPU

W atchdogtim er

Debuginterface

Power-onreset

Ports withinterrupt

facility (2)

PW MTim er

Analoguecom parator

C lock

Mixed signal processor structure - Texas MSP430


ROM

RAM

Processorcore

Custom I/Ointerface

Custom power-m anagem ent

unit

CustomMMU

Customperipheralsand debuginterface

Custom co-processor

On-chip databus (OCB)

Externalbus

Example system-on-a-chip (SOC) design


Review of section

You should now:

Clearly understand the important features of real-time systems. Know what sets them apart from batch and interactive application. See how real-time systems may be categorized in terms of speed and criticality. Have a general understanding of the range of real-time (and especially embedded)

applications. Realize that environmental and performance factors are key drivers in real-time

systems design. Know the basic component parts of real-time computer units. Appreciate the essential differences between microprocessors, microcomputers and

microcontrollers. Realize why there is a large market for specialized processors.

END OF SECTION ‘Introduction to real-time systems’

Review of ‘Introduction to real-time systems’

SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Introduction to real-time systems - slide 1 Software engineering for real-time systems.

Documents

realtime systems j

realtime systems section

introduction slide

software engineering

hardfast systems

soft systems deadlines

fast systems responses

hard systems emphasis