
Glossary of Terms and Abbreviations
Glossary-9
Quad word
. A group of 16 contiguous locations starting at an address
divisible by 16.
Quiesce
. To come to rest. The processor is said to quiesce when an exception
is taken or a
sync
instruction is executed. The instruction stream is
stopped at the decode stage and executing instructions are allowed to
complete to create a controlled context for instructions that may be
affected by out-of-order, parallel execution.
See
Context
synchronization.
Reservation
. The processor establishes a reservation on a
cache block
of
memory space when it executes an
lwarx
instruction to read a
memory semaphore into a GPR.
Reserved field.
In a register, a reserved field is one that is not assigned a
function. A reserved field may be a single bit. The handling of
reserved bits is
implementation-dependent
. Software is permitted to
write any value to such a bit. A subsequent reading of the bit returns
0 if the value last written to the bit was 0 and returns an undefined
value (0 or 1) otherwise.
RISC (reduced instruction set computing)
. An
architecture
characterized
by fixed-length instructions with nonoverlapping functionality and
by a separate set of load and store instructions that perform memory
accesses.
Segment
. A 256-Mbyte area of
virtual memory
that is the most basic memory
space defined by the PowerPC architecture. Each segment is
configured through a unique
segment descriptor
.
Segment descriptors
. Information used to generate the interim
virtual
address
. The segment descriptors reside in 16 on-chip segment
registers for 32-bit implementations.
Set
(
v
). To write a nonzero value to a bit or bit field; the opposite of
clear
. The
term ‘set’ may also be used to generally describe the updating of a
bit or bit field.
Set
(
n
). A subdivision of a
cache
. Cacheable data can be stored in a given
location in any one of the sets, typically corresponding to its lower-
order address bits. Because several memory locations can map to the
same location, cached data is typically placed in the set whose
cache
block
corresponding to that address was used least recently.
See
Set-associativity.
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