116314900 Real Time Systems 7th Sem ECE VTU Unit 1 Introduction to Real Time Systems Ramisuniverse

8/11/2019 116314900 Real Time Systems 7th Sem ECE VTU Unit 1 Introduction to Real Time Systems Ramisuniverse

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REAL TIME SYSTEMS

UNIT 1: INTRODUCTION TO REAL-TIME SYSTEMS:Historical background,

RTS Definition, Classification of Real-time Systems, Time constraints, Classification ofPrograms. 6 Hours

Historical backrou!"

Brown and Cambell ! "#$% ! &arliest roosal - Comuter oerating in real time

'as a art of t(e control system)

Consists of feedback and feed-forward loos

*ssumtion was t(at, t(e analog comuters can be used

Digital comuter elements did not were e+cluded

irst digital comuter ! deeloed for real time control ! for airborne oeration

Digitrac digital comuter ! "#$ ! used to roide an automatic flig(t and

weaons control system

/ndustrial control ! in digital comuters usage ! late "#$%s

Comuter and electronic system manufacturers ! for e+tending markets ! been

out from military uses of ! initiated t(e comuter control industries

"#$0, Setember ! 1ouisiana Power and 1ig(t Comany - Daystrom comuter

system2s installation ! for lant monitoring ! in t(eir ower station ! at Sterling,

1ouisiana

/t was not t(e control system

irst industrial comuter installation -

Te+aco Comany !Ramo-3ooldridge Comany - R3-4%% system2s installation -

at Port *rt(ur refinery in Te+as

"#$#, 5arc( "$t(! Refinery were using ! closed loo control system

'*non, "#$#)


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"#$6-$0 - 5onsanto C(emical Comany ! wit( t(e cooeration of Ramo-

3ooldridge Comany ! studied t(e control by comuter

"#$0, 7ctober ! it lanned to (ae comuter control for ammonia lant ! at

1uling, 1ouisiana

"#8%, 9uly :%t(! Commissioning of comuter control for ammonia lant at

1uling, 1ouisiana ! began

"#8%, *ril t(! Closed loo control was ac(ieed ! after rewriting ! t(e control

of t(e rogram - ;oise roblems ! were faced ! on t(e measurement of signals

"#$#-8%, B. . ation calculations ! for determining t(e set-oints ! for standard analog

controllers ! Here, comuter ! not controlling directly ! moement of t(e ales

or ot(er lant actuators

"#$# ! Plan to (ad t(e following installation were begun 'Burkitt,"#8$)

"#8:, ;oember ! erranti *rgus :%% systems - irst DDC 'Direct Digital

Control) system ! installed ! at /C/ ammonia-soda lant at leetwood,

1ancas(ire, ?=

/t was t(e large system ! ":% control loos '# of were used actually) ! :$8

measurements ':: of were used actually) ! in leetwood system

"#8" ! 5onsanto Comany ! Te+as city lant ! and, a (ierarc(ical control

sc(eme for etroc(emical comanies, at C(ocolate Bayou ! DDC ro@ects !

began

R3-4%% comuter ! used t(e rotating drum store ! to (old t(e control rogram


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erranti *rgus :%% ! ?sed t(e ferrite core store ! to (old t(e control rogram -

PR75 ! rogram was (eld in it

1oaded by ! (ysically inserting egs into a lug board ! eac( eg reresenting !

one bit in t(e memory word

3as laborious to set u initially

3as ery reliable !since, destruction of t(e memory contents - can be done only

by (ysical dislodgement of t(e egs

Security was en(anced ! using secial ower sulies ! and, switc(-oer

mec(anisms ! to rotect information (eld in t(e main core store

T(e information ! was as follows !

". Set oints ! 1oss most undesirable

:. Aale demand ! Presence after controlled stoage allows comuter to gain

control of lant immediately and wit(out disturbing t(e lant 'referred to as

bumless transfer)

4. 5emory calculations ! 1oss is tolerable, soon will be udated and only slig(t

disturbance to lant

. uture deeloment ! &+tension to allow for otimi>ation may reuire

information to be maintained for long eriods of time$. 5ore raid memory access ! were in erranti *rgus :%% ! t(at of R3-4%% and

similar mac(ines

Began t(e second (ase of alication of comuters ! to real time control

"#8%s, &arly ! Comuters ware using ! combined magnetic core memories and

drum stores ! drum eentually giing way to (ard disk dries

E#$:for early "#8%s comuters !


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erranti *rgus series

&lliot *utomation #%% series

Cost of earlier comuter increased ! in attemts to resole some roblems ! and

only one comuter ! for suerising control and DDC ! can be @ustified only ! it

was wit( furt(er roblems in deeloment of softwares

Softwares ! written by secialists rogrammers ! in mac(ine code ! it was

manageable earlier ! since, tasks were defined clearly and t(e rograms2 lengt(

were less

Combining of DDC and suerisory control ! increased !

". t(e code lengt(, for a gien alication

:. t(e comle+ity of t(e rogramming

DDC and suerisory control ! were wit( ery different time-scales

DDC control rograms ! (ae to interrut t(e suerisory control rograms2

increase in code lengt( ! made all t(e code could be stored in core memory and

also swaing of code between t(e drum memory and core ! to be to done were

also - Solutions to increased code lengt( roblems aboe ! were by -

Deeloment of general urose real-time oerating systems and (ig(-leel

languages

1ate "#8%s ! RT7S were deeloed ! PR7C&SS 7RTR*; comilers (ad t(eir

aearance

Problems and costs of inoling in (aing one comuter only for use ! made t(e

users to retreat ! t(e smaller systems ! for w(ic( newly deeloing

microcomuters 'like D&C PDP-0, PDP-"", Data


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5icrocomuters less cost ! made t(em suitable ! to load t(e large number of

tasks onto one mac(ine, 'by using more t(an one microcomuter, instead a single

comuter)

"#6% ! two comuters on t(e systems were using ! in w(ic( one comuter acting

simly stand-by ! to function in t(e eent of failure of t(e working comuter

T(roug(out "#6% ! Deeloments in /Cs and construction tec(niues in circuit

boards ! led to - increment in reliability of t(e systems ! reduction in t(e cost !

increment in t(e rocessor ower ! increase in t(e fast memory amount ! made

more correct and deendable softwares to be to write

"#6 ! microrocessors2 adent ! made it economical to use distributed comuter

control system

RTS D%&i!itio!

RTS "%&i!itio! 'i! as T(% O#&or" "ictio!ar) o& Co*+uti!,:

*ny system in w(ic( t(e time at w(ic( t(e outut is roduced is significant. T(is

is usually because t(e inut corresonds to some moement in t(e (ysical world,

and t(e outut (as to relate to t(at same moement. T(e lag from inut time to outut

time must be sufficiently small for accetable timelines

RTS "%&i!itio! 'Cooli! 1..1,:

Real-time systems are t(ose w(ic( must roduce correct resonses wit(in adefinite time limit. S(ould comuter resonses e+ceed t(ese time bounds t(en

erformance degradation andor malfunction results

RTS "%&i!itio! 'alt%r!at% "%&i!itio!,:


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* real-time system reads inuts from t(e lant and sends control signals to t(e

lant at times determined by lant oerational considerations ! not at times limited by

t(e caabilities of t(e comuter system

RTS "%&i!itio!:

* rogram for w(ic( t(e correctness of oerations deends bot( on t(e logical

results of t(e comutations and t(e time at w(ic( t(e results are roduced

E#$:*ircraft engine control system ! sending resonse to ?;/ workstations

Classi&icatio! o& R%al-ti*% S)st%*s

Comuter is connected to t(e enironment wit(in w(ic( it is working by a wide

range of interface deices and receies an sends a ariety of stimuli ! in t(e real time

systems and embedded comuters

&+.E Plant inut, lant outut, and communication tasks s(own in ig.


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T(ey (ae one common feature ! t(at t(ey are connected by (ysical deices to

rocesses w(ic( are e+ternal to t(e comuter. T(ese e+ternal rocesses all oerate in t(eir

own time scales and t(e comuter is said to oerated / real time if actions carried out in

t(e comuter relate to t(e time scales of t(e e+ternal rocesses

Sync(roni>ation between t(e e+ternal rocesses and t(e internal actions 'tasks) !

carried by t(e comuterE

". Clock basedE Sync(roni>ation between t(e aboe two - if in deends on assages of

time, actual time of day 'clock based RTS)

:. &ent basedE Sync(roni>ation between t(e aboe two ! if in deends eents

E#$:Closure of a switc(

4. /nteractie SystemsE Relation between t(e actions in t(e comuter and t(e system ! is

muc( more loosely defined

Reuirement, tyically ! in t(e form t(at ! a set of oerations in t(e comuter s(ould be

comleted wit(in a redetermined time

5a@ority of t(e communication tasks ! are of t(is category

Co!trol tasks: &en t(oug( ! not obiously and directly connected to t(e e+ternal

enironment ! t(ey need to oerated in real time ! since, time is usually inoled in

determining t(e arameters of t(e algorit(ms used. /t is useful to diide tasks to be

carried out by embedded comuters into t(e interactie categories and c(aracteristics of

eac( class are to be recogni>ed

T)+%s o& tasks i! r%al ti*% s)st%*s:T(e t(ree tyes of tasks are


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". Clock-based 'Cyclic, Periodic)

:. &ent-based '*eriodic)

4. /nteractie systems

1$ Clock-bas%" Tasks 'C)clic/ 0%rio"ic,

Process of t(e lant - oerate in real time

Plant time constantE it2s t(e measure of t(e time taken by a lant to resond to a c(ange in

inut or load and is used as a c(aracteristic of t(e lant

5ay be measured ! in (ours for some c(emical rocesses or

/n ms for an aircraft system

eedback controlE /t inoles t(e feedback control

/t reuires t(e samling rate to be deendent on t(e time constant of t(e rocess to be

controlled

Samling rate increases ! as t(e time constant alue decreases

Sync(roni>ation in real time ! between t(e two is ! reuired

*ll t(e reuired oerations 'like measurement, control and actuation ! wit(in eac(

samling interal) ! can be able to carry out

Comletion of t(e oeration ! wit(in t(e secified timeE Deendent on

". ;umber of oerations to be erformed

:. Seed of t(e comuter

R%al-ti*% clock:/t2s t(e clock ! added to t(e comuter - to (ae t(e sync(roni>ation. /t2s

signal ! is used to interrut t(e oerations of t(e comuter ! at some redetermined fi+ed

time interal

Comuters carry out ! lant inut, lant outut and control tasks in resonse to t(e clock

interrut. /f t(e clock interrut is at a faster rate t(an t(e samling rate ! count of eac(

interrut to be to ! until it2s t(e time to run t(e tasks.

Different samling ratesE used in larger lants ! w(ere tasks are subdiided into grous !

for controlling different arts of t(e lant


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Clock interrut ! used freuently ! to kee a clock and a calendar ! and kee t(e

comuter ! aware of bot( t(e time and t(e date

Clock based tasks 'cyclic or eriodic tasks) ! (ere, task is run once er time eriod T

'cycle time, T) !or run at e+actly T unit interals

2. E%!t-bas%" Tasks 'A+%rio"ic,

Systems in w(ic( actions are erformed in resonse to some eents and not

erformed at resonse at articular times or time interals

E#$:

". Turing off a um - Closing a ale w(en t(e leel of a liuid tank reac(es

redetermined alue ! like t(e one in - leel of fuel in t(e e(icle fuel tank ! reac(ing

t(e um no>>le

:. Switc(ing a motor off ! in resonse to t(e closure of a micro-switc(

indicating - t(at some desired osition (ad reac(ed

?sed e+tensiely ! to indicate ! alarm conditions and initiate alarm actions

&+.E /ndication of too (ig( a temerature or too great a ressure

/ncludes t(e reuirement! t(at t(e system must resond ! wit(in a gien ma+imum time

to a articular eent

?ses t(e interruts ! to inform t(e comuter system ! t(at action is reuired. Smaller

systems ! use olling - w(ere t(e comuter eriodically asks 'olls) arious sensors ! to

see if action is reuired

*eriodic tasksE &ents usually occur at non-deterministic interals

*eriodic tasks ! may (ae deadlines ! e+ressed in terms of (aing start times or finis(

times or een bot(.

&+.E Task may be reuired to start ! wit(in %.$s of an eent occurring

Task may (ae to roduce an outut ! wit(in %.$s of an eent

2$ I!t%racti% s)st%*s

Probably reresent ! t(e largest class of real time systems

E#$: ". *utomatic bank tellers


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:. Reseration systems for (otels, airlines and car rental comanies

4. Comuteri>ed tills

Reuirement of interactie systemsE can be e+ressed in terms suc( as Ft(e aerage

resonse tome must not e+ceedG2

&+.E *utomatic bank teller system mig(t ! reuire an aerage resonse time ! not

e+ceeding :%s

E%!t-bas%" s)st%*s 3s I!t%racti% s)st%*s

T(e two are

1. Sa*%:since, it aarently resonse to a signal from t(e lant 'in t(is case usually

a erson)

2. Di&&%r%!t:Since, it resonds a a time determined by t(e internal state of t(e

comuter and wit(out any reference to t(e enironment

&+.E *utomatic bank teller - does not know t(at ! you will miss a train, or t(at it2s

raining (ard and you are getting wet, but it2s resonse ! deends on (ow busy t(e

communication lines and central comuters are and also your amount

Clock-bas%" s)st%*s 3s I!t%racti% s)st%*sT(e two are

1. Sa*%:since, are caable of dislaying t(e date and time, and also t(ey (ae a real

time clock ! w(ic( enables t(em to kee track of time

2. Di&&%r%!t:w(en t(e test is done w(et(er or not t(e answer for t(e uestion ! FCan

t(e system be tig(tly sync(roni>ed to an e+ternal rocess2

/f answer is Fyes2 ! t(ey are clock-based

/f answer is Fno2 ! t(ey are eent-based

116314900 Real Time Systems 7th Sem ECE VTU Unit 1 Introduction to Real Time Systems Ramisuniverse

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Transcript of 116314900 Real Time Systems 7th Sem ECE VTU Unit 1 Introduction to Real Time Systems Ramisuniverse