Motorola MPC860 PowerQUICC, User Manual, Page: 1085 / 1106

MOTOROLA Glossary of Terms and Abbreviations Glossary--11
base user-level instruction set, user-level registers, data types,
ßoating-point memory conventions and exception model as seen by
user programs, and the memory and programming models.
User mode. The unprivileged operating state of a processor used typically by
application software. In user mode, software can only access certain
control registers and can access only user memory space. No
privileged operations can be performed. Also referred to as problem
state.
VEA (virtual environment architecture). The level of the architecture that
describes the memory model for an environment in which multiple
devices can access memory, deÞnes aspects of the cache model,
deÞnes cache control instructions, and deÞnes 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.
Watchpoint. An event that is reported, but does not change the timing of the
machine.
Word. A 32-bit data element. Note that on other processors a word may be a
different size.
Write-back. A cache memory update policy in which processor write cycles
are directly written only to the cache. External memory is updated
only indirectly, for example, when a modiÞed cache block is cast out
to make room for newer data.
Write-through. A cache memory update policy in which all processor write
cycles are written to both the cache and memory.
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