14 www.xilinx.com PowerPC™ 405 Processor Block Reference Guide
1-800-255-7778 UG018 (v2.0) August 20, 2004
Preface: About This Guide
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exception An abnormal event or condition that requires the processor’s
attention. They can be caused by instruction execution or an
external device. The processor records the occurrence of an
exception and they often cause an interrupt to occur.
fill buffer A buffer that receives and sends data and instructions between
the processor and PLB. It is used when cache misses occur and
when access to non-cacheable memory occurs.
flush A cache operation that involves writing back a modified entry
to memory, followed by an invalidation of the entry.
GB Gigabyte, or one-billion bytes.
halfword Two bytes, or 16 bits.
hit An indication that requested information exists in the accessed
cache array, the associated fill buffer, or on the corresponding
OCM interface.
inactive As applied to signals, this term indicates a signal is in a state
that does not cause an action to occur, nor does it indicate an
action occurred. An active-high signal drives a logic 0 when
inactive. An active-low signal drives a logic 1 when inactive.
interrupt The process of stopping the currently executing program so that
an exception can be handled.
invalidate A cache or TLB operation that causes an entry to be marked as
invalid. An invalid entry can be subsequently replaced.
KB Kilobyte, or one-thousand bytes.
line buffer A buffer located in the cache array that can temporarily hold the
contents of an entire cache line. It is loaded with the contents of
a cache line when a cache hit occurs.
line fill A transfer of the contents of the instruction or data line buffer
into the appropriate cache.
line transfer A transfer of an aligned, sequentially addressed 4-word or 8-
word quantity (instructions or data) across the PLB interface.
The transfer can be from the PLB slave (read) or to the PLB slave
(write).
little endian A memory byte ordering where the address of an item
corresponds to the least-significant byte.
logical address Synonym for effe ctive address.
MB Megabyte, or one-million bytes.
memory Collectively, cache memory and system memory.
miss An indication that requested information does not exist in the
accessed cache array, the associated fill buffer, or on the
corresponding OCM interface.