
MOTOROLA
Glossary of Terms and Abbreviations
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Glossary-13
Shadowing.
Shadowing allows a register to be updated by instructions that
are executed out of order without destroying machine state
information.
Signaling NaN.
A type of
NaN
that generates an invalid operation program
exception when it is specified as arithmetic operands. See
Quiet
NaN
.
Significand.
The component of a binary floating-point number that consists
of an explicit or implicit leading bit to the left of its implied binary
point and a fraction field to the right.
Simplified mnemonics.
Assembler mnemonics that represent a more
complex form of a common operation.
Slave.
The device addressed by a master device. The slave is identified in the
address tenure and is responsible for supplying or latching the
requested data for the master during the data tenure.
Snooping.
Monitoring addresses driven by a bus master to detect the need
for coherency actions.
Snoop push.
Response to a snooped transaction that hits a modified cache
block. The cache block is written to memory and made available to
the snooping device.
Split
-
transaction.
A transaction with independent request and response
tenures.
Split-transaction bus.
A bus that allows address and data transactions from
different processors to occur independently.
Stage.
The term
stage
is used in two different senses, depending on whether
the pipeline is being discussed as a physical entity or a sequence of
events. In the latter case, a stage is an element in the pipeline during
which certain actions are performed, such as decoding the
instruction, performing an arithmetic operation, or writing back the
results. Typically, the latency of a stage is one processor clock cycle.
Some events, such as dispatch, write-back, and completion, happen
instantaneously and may be thought to occur at the end of a stage. An
instruction can spend multiple cycles in one stage. An integer
multiply, for example, takes multiple cycles in the execute stage.
When this occurs, subsequent instructions may stall. An instruction
may also occupy more than one stage simultaneously, especially in
the sense that a stage can be seen as a physical resource—for
example, when instructions are dispatched they are assigned a place
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.