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# Resynchronization of Quasi-Periodic Branches

IP.com Disclosure Number: IPCOM000106721D
Original Publication Date: 1993-Dec-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 81K

IBM

## Related People

Ekanadham, K: AUTHOR [+5]

## Abstract

Consider a branch instruction (BC) that has a dominant cycle pattern, with respect to a single taken target and overall quasi-periodic with respect to both taken and non-taken targets. The simplest example of such a pattern for a branch that has two targets {T1, T2} is:

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Resynchronization of Quasi-Periodic Branches

Consider a branch instruction (BC) that has a dominant cycle
pattern, with respect to a single taken target and overall
quasi-periodic with respect to both taken and non-taken targets.  The
simplest example of such a pattern for a branch that has two targets
{T1, T2} is:

P1,P2,P1,P2,P1,P2,P1,P2,P1,P2

where

P1 = (a, b sub 1 )

a= # of successive actions to T1

b sub 1  = # of successive actions to T2

P2 = (a, b sub 2 )

b sub 2 = # of successive actions to T2

The aspect of the branch that makes it have a major cyclic
dominant is that one target only occurs in succession "a" times.
That which makes it quasi-periodic as opposed to periodic is the fact
that the pattern is not <(P1, P2)> sup n.  The detection and
predictor formulation for such a quasi-periodic branch involves:
first assuming a period and then deriving a consensus using for the
frequency of the individual b sub i  values within the assumed
period.  However, if the pattern exhibits a phase shift by repeating
P2  and then goes back to the original pattern  i.e.,

P1,P2,P1,P2,P1,P2,P1,P2,P1,P2,P1,P2,P2,P1,P2,P1,P2,P1,P2,P1,P2,P1,P2
one needs to distinguish this case from a error in a symbol within
the basic periodicity of the quasi-periodic branch as only consensus
values were used.

The method which works and is generalizable to an arbitrary number of
symbols is to:

o   recognize that such a possibility exists and can be caused by the
viewing of a marginal action of a single branch within a joint
recursive branch action sequence.

o   Monitor periodic branches with respect to a resynchronization
tester which predicts successor symbols.  If the successor symbol
predictor indicates that a phase shift has occurred, a
resynchronization of the pattern is performed.

o   RESYNCHRONIZATION ALGORITHM

The algorithm for resynchronization requires three "correct"
successors from the resynchronization tester for which which the
quasi-periodic predictor is wrong on all unique symbols.

The action of the resynchronization can best be explained by
considering the following quasi-periodic predictor:

P1,P2,P1,...