Time Redundancy

8/7/2019 Time Redundancy

1/39


2/39


3/39

It Involves the Repetition or Rollback ofinstructions , Segment of programs or entire

programs immediately after a fault isdetected.

Rollback operation requires that a programrestarts processing from the last check point ,

where all the information relevant to thesuccessful execution of the program beyondthe check point is stored .


4/39

The Selection of correct number of checkpoints is important .

If too many check points are used , the computation timeincreases since the normal flow of the program is stopped ateach check point in order to save state information.

The Recovery time will increase even if the check points are

too far apart since the program will have to be re-executedfrom the last check point .

The optimum check point interval is to be chosen to get theoptimum recovery time.


5/39

If the fault is temporary , Rolling back the

program to a check point should allowsuccessful recovery .

If the fault is permanent , the fault detectionmechanism will be activated and analternative recovery method should beattempted.


6/39


7/39

Distinguishing between Transient and

Permanent Faults


8/39


9/39


10/39


11/39


12/39


13/39


14/39


15/39


16/39


17/39

The Key Advantage of Alternating Logic is that any

combinational circuit with n input variables can be transformed

into a self dual circuit with no more than n+1 variables

The dual of an n variable function f is given by

fd

= f_

( X1 ,_

X2 ,

_

, .. , Xn )

_

The function Fsd is Given by

fsd =

xn+1

f + xn+1 fd

_

Here Fsd is the

transformed

Self dual circuit of F


18/39


19/39


20/39


21/39


22/39

Errordetection

mechanism

of ALU using

RESO

Technique


23/39

The additional hardware required for thistechnique is the three shifters , the storageregister to hold the results of the first

computation and the comparator also. Also, the ALU must be extended by 2 bits to

allow a two bit , arthematic shift to beperformed.

Due to this extra bits required , we will go for

RESWO approach


24/39


25/39


26/39

During the first computation, the operandsare manipulated in their standard form .

During the second computation , the upper

and lower halves of the operands are swappedsuch that a faulty bit slice operates on eitherthe lower or upper half of the operands duringthe first computation and the upper or lowerhalf of the operands during the secondcomputation .


27/39

At t0,C1AC

C2Cout

At t0+

C1Cout

C2AC


28/39


29/39

This method takes advantage of both Time

Redundancy and Hardware Redundancy.

In both RESO and RESWO methods error

detection is performed with the help of time

redundancy

But In this method,error detection accomplished

resembles that of duplication with comparision . Then Time redundancy is then used to complete

the calculation and obtain the final result


30/39


31/39


32/39

For example, a 32 bit addition operation can

be realized by using each of two 16 bit adders

twice .

During each calculation, error detection is

accomplished by comparing the results from

using the two adders .


33/39

32 bit

swapper

consists of32

2 -1 MUXs


34/39

Time redundancy can provide error correction

if the computations are repeated for 3 ormore times.

Consider the logical and operation that was

illustrated in RESO method .


35/39

OPERATION 1:

without shifting

OPERATION 2:

1BIT LEFT SHIFT

W.R.T ORIGINAL DATA


36/39

OPERATION 3:

3BITS LEFT SHIFT

W.R.T. ORIGINAL DATA

By performing a majority vote on the 3 results

Error due to faulty bit slice can be corrected.


37/39

Each of the three operations used operands

that were displaced from each other by atleast

one bit position , a different bit in each result

will be affected by the fault of bit slice .

The results due to faulty bit slice can corrected

by performing a majority vote on the three

results obtained for each bit position


38/39

CONTRIBUTION

D.V.R.Reddy

Ramesh

Satesh

jitender

Gufran

Dubey

Jignesh

thakur


39/39

References

P.k.lala

Barry W. Johnson

Time Redundancy

Documents

Transcript of Time Redundancy