Xilinx Virtex-II Pro PPC405, Руководство пользователя

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March 2002 Release www.xilinx.com 359
Virtex-II Pro™ Platform FPGA Documentation 1-800-255-7778
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Chapter 3
User Programming Model
This chapter describes the processor resources and instructions available to all programs
running on the PPC405, whether they are running in user mode or privileged mode. These
resources and instructions are referred to as the
user-programming model , which is a subset
of the privileged-programming model. Applications are typically restricted to running in
user mode. System software runs in privileged mode and has access to all register
processor resources, and can execute all instructions supported by the PPC405. System
software typically creates a context (execution environment) that protects itself and other
applications from the effects of an errant application program.
The remaining chapters in this book generally describe aspects of the privileged-
programming model and are not relevant to application programmers. There are two
exceptions:
• Chapter 5, Memory-System Management , describes cache management features
available to both system and application programs.
• Chapter 8, Timer Resources , describes the time base, which can be read by
application programs.
User Registers
Figure 3-1 shows the user registers supported by the PPC405, all of which are available to
software running in user mode and privileged mode. In the PPC405, all user registers are
32-bits wide, except for the time base as described in
Time Base , page 524 . Floating-point
registers are not supported by the PPC405.