Sun Microelectronics
361
. Glossary
should:
A key word indicating flexibility of choice with a strongly preferred imple-
mentation. The phrase “it is recommended” is used interchangeably with the
key word should.
side effect:
A memory location is deemed to have side effects if additional actions
beyond the reading or writing of data may occur when a memory operation
on that location is allowed to succeed. Locations with side effects include
those that, when accessed, change state or cause external events to occur. For
example, some I/O devices contain registers that clear on read, others have
registers that initiate operations when read.
snooping:
The process of maintaining coherency between caches in a shared-memory
bus architecture. All cache controllers monitor (snoop) the bus to determine
whether they have a copy of a shared cache block.
speculative load:
A load operation (e.g., non-faulting load) that is carried out before it is known
whether the result of the operation is required. These accesses typically are
used to speed program execution. An implementation, through a combina-
tion of hardware and system software, must nullify speculative loads on
memory locations that have side effects; otherwise, such accesses produce
unpredictable results.
supervisor software:
Software that executes when the processor is in privileged mode.
TLB hit:
The desired translation is present in the on-chip TLB.
TLB miss:
The desired translation is not present in the on-chip TLB.
Translation Lookaside Buffer (TLB):
A hardware cache located within the MMU, which contains copies of recently
used translations. Technically, there are separate TLBs for the instruction and
data paths; the I-MMU contains the iTLB and the D-MMU the dTLB.
trap:
A vectored transfer of control to supervisor software through a table, the
address of which is specified by the privileged Trap Base Address (TBA) reg-
ister.
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