
Glossary-4
G2 PowerPC Core Reference Manual
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MOTOROLA
Context synchronization.
An operation that ensures that all instructions in
execution complete past the point where they can produce an
exception
, that all instructions in execution complete in the context
in which they began execution, and that all subsequent instructions
are
fetched
and executed in the new context. Context
synchronization may result from executing specific instructions
(such as
isync
or
rfi
) or when certain events occur (such as an
exception
).
Copy-back operation.
A cache operation in which a cache line is copied
back to memory to enforce cache coherency. Copy-back operations
consist of snoop push-out operations and cache cast-out operations.
D
Denormalized number.
A nonzero floating-point number whose exponent
has a reserved value, usually the format's minimum, and whose
explicit or implicit leading significand bit is zero.
Direct-mapped cache.
A cache in which each main memory address can
appear in only one location within the cache, operates more quickly
when the memory request is a cache hit.
Direct-store segment access.
An access to an I/O address space. The G2
defines separate memory-mapped and I/O address spaces, or
segments, distinguished by the corresponding segment register T bit
in the address translation logic of the G2. If the T bit is cleared, the
memory reference is a normal memory-mapped access and can use
the virtual memory management hardware of the G2. If the T bit is
set, the memory reference is a direct-store access.
E
Effective address (EA).
The 32-bit address specified for a load, store, or an
instruction fetch. This address is then submitted to the MMU for
translation to either a
physical memory
address or an I/O address.
Exception.
A condition encountered by the processor that requires special,
supervisor-level processing.
Exception handler.
A software routine that executes when an exception is
taken. Normally, the exception handler corrects the condition that
caused the exception, or performs some other meaningful task (that
may include aborting the program that caused the exception). The
address for each exception handler is identified by an exception
vector offset defined by the architecture and a prefix selected via the
MSR.
F
Freescale Semiconductor, Inc.
n
.