Glossary-4
MPC7400 RISC Microprocessor Users Manual
Denormalized number
.
A nonzero oating-point number whose exponent
has a reserved value, usually the format's minimum, and whose
explicit or implicit leading signiTcand 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.
Effective address (EA)
. The 32- or 64-bit address speciTed 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 identiTed by an exception
vector offset deTned by the architecture and a preTx selected via the
MSR.
Execution synchronization
. A mechanism by which all instructions in
execution are architecturally complete before beginning execution
(appearing to begin execution) of the next instruction. Similar to
context synchronization but doesn't force the contents of the
instruction buffers to be deleted and refetched.
Exponent
.
In the binary representation of a oating-point number, the
exponent is the component that normally signiTes the integer power
to which the value two is raised in determining the value of the
represented number.
See also
Biased exponent.
Fall-through (branch fall-through)
A not-taken branch. On the
MPC7400, fall-through branch instructions are removed from the
instruction stream at dispatch. That is, these instructions are allowed
to fall through the instruction queue via the dispatch mechanism,
without either being passed to an execution unit and or given a
position in the completion queue.
Fetch
. Retrieving instructions from either the cache or main memory and
placing them into the instruction queue.
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