
Glossary-2
G2 PowerPC Core Reference Manual
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
Big-endian.
A byte-ordering method in memory where the address
n
of a
word corresponds to the
most-significant byte
. In an addressed
memory word, the bytes are ordered (left to right) 0, 1, 2, 3, with 0
being the
most-significant byte
. See
Little-endian
.
Block.
An area of memory that ranges from 128 Kbytes to 256 Mbytes
whose size, translation, and protection attributes are controlled by
the
BAT
mechanism.
Boundedly undefined.
A characteristic of certain operation results that are
not rigidly prescribed by the PowerPC architecture. Boundedly-
undefined results for a given operation may vary among
implementations and between execution attempts in the same
implementation.
Although the architecture does not prescribe the exact behavior for
when results are allowed to be
boundedly
undefined
, the results of
executing instructions in contexts where results are allowed to be
boundedly undefined
are constrained to ones that could have been
achieved by executing an arbitrary sequence of defined instructions,
in valid form, starting in the state the machine was in before
attempting to execute the given instruction.
Branch folding.
The replacement with target instructions of a branch
instruction and any instructions along the not-taken path when a
branch is either taken or predicted as taken.
Branch prediction.
The process of guessing whether a branch will be taken.
Such predictions can be correct or incorrect; the term ‘predicted’ as
it is used here does not imply that the prediction is correct
(successful). The PowerPC architecture defines a means for
static
branch
prediction as part of the instruction encoding.
Branch resolution.
The determination of whether a branch is taken or not
taken. A branch is said to be resolved when the processor can
determine which instruction path to take. If the branch is resolved as
predicted, the instructions following the predicted branch that may
have been speculatively executed can complete (see
Completion
). If
the branch is not resolved as predicted, instructions on the
mispredicted path, and any results of speculative execution, are
purged from the pipeline and fetching continues from the
nonpredicted path.
Burst.
A multiple-beat data transfer whose total size is typically equal to a
cache block.
F
Freescale Semiconductor, Inc.
n
.