
MOTOROLA
Glossary of Terms and Abbreviations
For More Information On This Product,
Go to: www.freescale.com
Glossary-15
Transaction.
A complete exchange between two bus devices. A transaction
is typically comprised of an address tenure and one or more data
tenures, which may overlap or occur separately from the address
tenure. A transaction may be minimally comprised of an address
tenure only.
Transfer termination.
Signal that refers to both signals that acknowledge
the transfer of individual beats (of both single-beat transfer and
individual beats of a burst transfer) and to signals that mark the end
of the tenure.
U
UISA (user instruction set architecture).
The level of the architecture to
which user-level software should conform. The UISA defines the
base user-level instruction set, user-level registers, data types,
floating-point memory conventions and exception model as seen by
user programs, and the memory and programming models.
Underflow.
A condition that occurs during arithmetic operations when the
result cannot be represented accurately in the destination register.
For example, underflow can happen if two floating-point fractions
are multiplied and the result requires a smaller
exponent
and/or
mantissa
than the single-precision format can provide. In other
words, the result is too small to be represented accurately.
User mode.
The operating state of a processor used typically by application
software. In user mode, software can access only certain control
registers and can access only user memory space. No privileged
operations can be performed. Also referred to as problem state.
V
VEA (virtual environment architecture).
The level of the
architecture
that
describes the memory model for an environment in which multiple
devices can access memory, defines aspects of the cache model,
defines cache control instructions, and defines the time-base facility
from a user-level perspective.
Implementations
that conform to the
PowerPC VEA also adhere to the UISA, but may not necessarily
adhere to the OEA.
Virtual address.
An intermediate address used in the translation of an
effective address
to a physical address.
Virtual memory.
The address space created using the memory management
facilities of the processor. Program access to
virtual
memory
is
possible only when it coincides with
physical memory
.
F
Freescale Semiconductor, Inc.
n
.