
Glossary-4
PowerPC Microprocessor Family: The Bus Interface for 32-Bit Microprocessors
Effective address (EA)
. The 32- or 64-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.
E
xception
. 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.
Exclusive state.
MESI state (E) in which only one caching device contains
data that is also in system memory.
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 floating-point number, the
exponent is the component that normally signifies the integer power
to which the value two is raised in determining the value of the
represented number.
See also
Biased exponent.
Feed-forwarding
. A feature that reduces the number of clock cycles that an
execution unit must wait to use a register. When the source register
of the current instruction is the same as the destination register of the
previous instruction, the result of the previous instruction is routed to
the current instruction at the same time that it is written to the register
file. With feed-forwarding, the destination bus is gated to the waiting
execution unit over the appropriate source bus, saving the cycles
which would be used for the write and read.
Fetch
. Retrieving instructions from either the cache or main memory and
placing them into the instruction queue.
E
F