
Glossary-2
PowerPC Microprocessor Family: The Bus Interface for 32-Bit Microprocessors
Block
. An area of memory that ranges from 128 Kbyte to 256 Mbyte, whose
size, translation, and protection attributes are controlled by the
BAT
mechanism.
Boundedly undefined
. A characteristic of results of certain operations 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.
Burst
. A multiple beat data transfer whose total size is typically equal to a
cache block.
Bus clock
. Clock that causes the bus state transitions.
Bus master
. The owner of the address or data bus; the device that initiates or
requests the transaction.
Cache
. High-speed memory component containing recently-accessed data
and/or instructions (subset of main memory).
Cache block
. A small region of contiguous memory that is copied from
memory into a
cache
. The size of a cache block may vary among
processors; the maximum block size is one
page
. In PowerPC
processors,
cache coherency
is maintained on a cache-block basis.
Note that the term ‘cache block’ is often used interchangeably with
‘cache line’.
Cache coherency
. An attribute wherein an accurate and common view of
memory is provided to all devices that share the same memory
system. Caches are coherent if a processor performing a read from
its cache is supplied with data corresponding to the most recent value
written to memory or to another processor’s cache.
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