rtft15 unit 2.pptx

7/25/2019 RTFT15 unit 2.pptx

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UNIT 2

Fault ToleranceFault-Error-Failure.

Redundancy,

Error Detection,

Damage Confnement,

Error Recovery,

Fault Treatment,

Fault Prevention,

anticiated and

unanticiated Fault!.

Roll No" #$

Error model!

Error detection tec%ni&ue!

'atc%dog

Error control coding.


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Fault

It i! !ome %y!ical de(ect t%at can cau!e a

comonent to mal(unction .

Fault can )e"

- *ard+are Fault eg" logical +ire

- o(t+are Fault eg" )ug

Real Time and Fault Tolerance

Defnition


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Fault:

Fault i! a de(ect +it%in t%e !y!tem

E/amle!"0 o(t+are )ug

0 Random %ard+are (ault

0 1emory )it !tuc34

E/amle



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Error

Error i! a deviation (rom t%e re&uired oeration o(

!y!tem or !u)!y!tem

5 6 (ault may lead to an error, i.e., error i! a

mec%ani!m )y +%ic% t%e (ault )ecome! aarent

5 Fault may !tay dormant (or a long time )e(ore it

mani(e!t! it!el( a! an error"


Defnition


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Error:

1emory )it got !tuc3 )ut CPU doe! not acce!! t%i!

data

o(t+are )ug4 in a !u)routine i! not vi!i)le4 +%ile

t%e !u)routine i! not called

E/amle



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Failure:

6 !y!tem (ailure occur! +%en t%e !y!tem (ail! toer(orm it! re&uired (unction

Pre!ence o( an error mig%t cau!e a +%ole !y!tem to

deviate (rom it! re&uired oeration

7ne o( t%e goal! o( !a(ety-critical !y!tem! i! t%at

error !%ould not re!ult in !y!tem (ailure

Defnition



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Need of fault tolerance

Comle/ !y!tem

Critical alication!

*ar!% Environment



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Redundancy

6ll (ault-tolerant tec%ni&ue! rely on e/tra element!

introduced into t%e !y!tem to detect 8 recover (rom(ault!

Comonent! are redundant a! t%ey are not re&uired

in a er(ect !y!tem

7(ten called rotective redundancy



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6im" minimi!e redundancy +%ile ma/imi!ing

relia)ility, !u)9ect to t%e co!t and !i:e con!traint!

o( t%e !y!tem

'arning" t%e added comonent! inevita)ly

increa!e t%e comle/ity o( t%e overall !y!tem

T%i! it!el( can lead to le!! relia)le !y!tem!

E.g" fr!t launc% o( t%e !ace !%uttle

It i! advi!a)le to !earate out t%e (ault-tolerant

comonent! (rom t%e re!t o( t%e !y!temReal Time and Fault Tolerance


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T+o tye!" !tatic or ma!3ing and dynamic

redundancy

tatic" redundant comonent! are u!ed in!ide a!y!tem to %ide t%e e;ect! o( (ault!< e.g. Trile 1odular

Redundancy T1R = > identical !u)comonent! and ma9ority voting

circuit!< t%e outut! are comared and i( one di;er!(rom t%e ot%er t+o t%at outut i! ma!3ed out

Dynamic" redundancy !ulied in!ide a comonent+%ic% indicate! t%at t%e outut i! in error< rovide! anerror detection (acility< recovery mu!t )e rovided )yanot%er comonent

E.g. communication! c%ec3!um! and memory arity)it!

*ard+are Redundancy



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y!tem i! rovided +it% di;erent !o(t+are ver!iono( ta!3

'ritten indeendently )y di;erent team o(

rogrammer!

I( one ver!ion o( ta!3 (ail under certain inut

anot%er ver!ion can )e u!edtatic"

N ver!ion

Recovery )loc3


o(t+are Redundancy


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Four %a!e!

Error detection = no (ault tolerance !c%eme can )eutili!ed until t%e a!!ociated error i! detected

Damage confnement and a!!e!!ment = to +%ate/tent %a! t%e !y!tem )een corruted? T%e delay

)et+een a (ault occurring and t%e detection o( t%e errormean! erroneou! in(ormation could %ave !readt%roug%out t%e !y!tem

Error recovery = tec%ni&ue! !%ould aim to tran!(ormt%e corruted !y!tem into a !tate (rom +%ic% it cancontinue it! normal oeration

Fault Treatment and continued !ervice = an error i! a

!ymtom o( a (ault< alt%oug% damage reaired, t%eReal Time and Fault Tolerance

o(t+are Redundancy dynamic tye


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T%e data are coded in !uc% a +ay t%at acertain num)er o( )it error can )e detected

or corrected


In(ormation Redundancy


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Error Detecting Technique

Parity c%ec3ing

C%ec3!um error detection

Cyclic Redundancy c%ec3

Finding error in fr!t lace



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Error Detection

7t%er tye! %eart)eat! etc.

Environmental detection

%ard+are = e.g. illegal in!truction

7.@RT = null ointer

6lication detection

Relication c%ec3!

Timing c%ec3! Rever!al c%ec3!

Coding c%ec3!

Rea!ona)lene!! c%ec3!

Types



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Damage Connement and Assessment

Damage a!!e!!ment i! clo!ely related to damage

confnement tec%ni&ue! u!ed

Damage confnement i! concerned +it% !tructuring t%e!y!tem !o a! to minimi!e t%e damage cau!ed )y a

(aulty comonent al!o 3no+n a! fre+alling

1odular decomo!ition rovide! !tatic damageconfnement< allo+! data to Ao+ t%roug% +ell-defneat%+ay!

6tomic action! rovide! dynamic damage confnement

rtft15 unit 2.pptx

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