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MPC7400 RISC Microprocessor Users Manual
This document and
The Programming Environments Manual
distinguish between the three
levels, or programming environments, of the PowerPC architecture, which are as follows:
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PowerPC user instruction set architecture (UISA)The UISA deTnes the level of
the architecture to which user-level software should conform. The UISA deTnes the
base user-level instruction set, user-level registers, data types, memory conventions,
and the memory and programming models seen by application programmers.
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PowerPC virtual environment architecture (VEA)The VEA, which is the smallest
component of the PowerPC architecture, deTnes additional user-level functionality
that falls outside typical user-level software requirements. The VEA describes the
memory model for an environment in which multiple processors or other devices can
access external memory and deTnes aspects of the cache model and cache control
instructions from a user-level perspective. The resources deTned by the VEA are
particularly useful for optimizing memory accesses and for managing resources in
an environment in which other processors and other devices can access external
memory.
Implementations that conform to the PowerPC VEA also conform to the PowerPC
UISA, but may not necessarily adhere to the OEA.
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PowerPC operating environment architecture (OEA)The OEA deTnes
supervisor-level resources typically required by an operating system. The OEA
deTnes the PowerPC memory management model, supervisor-level registers, and
the exception model.
Implementations that conform to the PowerPC OEA also conform to the PowerPC
UISA and VEA.
It is important to note that some resources are deTned more generally at one level in the
architecture and more speciTcally at another. For example, conditions that cause a
oating-point exception are deTned by the UISA, while the exception mechanism itself is
deTned by the OEA.
Because it is important to distinguish between the levels of the architecture in order to
ensure compatibility across multiple platforms, those distinctions are shown clearly
throughout this book.
For ease in reference, the arrangement of topics in this book follows that of
The
Programming Environments Manual
. Topics build upon one another, beginning with a
description and complete summary of MPC7400-speciTc registers and instructions and
progressing to more specialized topics such as MPC7400-speciTc details regarding the
cache, exception, and memory management models. As such, chapters may include
information from multiple levels of the architecture. (For example, the discussion of the
cache model uses information from both the VEA and the OEA.) The AltiVec logo in the
margin indicates a substantial reference to the AltiVec architecture.