22 www.xilinx.com PowerPC™ 405 Processor Block Reference Guide
1-800-255-7778 UG018 (v2.0) August 20, 2004
Chapter 1: Introduction to the PowerPC 405 Processor
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iWrite-back and write-through support
iProgrammable load and store cache line allocation
iOperand forwarding during cache line fills
iNon-blocking during cache line fills and flushes
xSupport for on-chip memory (OCM) that can provide memory-access performance
identical to a cache hit
xFlexible memory management:
iTranslation of the 4 GB logical-address space into the physical-address space
iIndependent control over instruction translation and protection, and data
translation and protection
iPage-level access control using the translation mechanism
iSoftware control over the page-replacement strategy
iWrite-through, cacheability, user-defined 0, guarded, and endian (WIU0GE)
storage-attribute control for each virtual-memory region
iWIU0GE storage-attribute control for thirty-two 128 MB regions in real mode
iAdditional protection control using zones
xEnhanced debug support with logical operators:
iFour instruction-address compares
iTwo data-address compares
iTwo d at a- va lu e c o mp ar es
iJTAG instruction for writing into the instruction cache
iForward and backward instruction tracing
xAdvanced power management support
The following sections describe the software resources available in the PowerPC 405. Refer
to the PowerPC Processor Reference Guide for more information on using these resources.
Privilege Modes
Software running on the PowerPC 405 can do so in one of two privilege modes: privileged
and user.

Privileged Mode

Privileged mode allows programs to access all registers and execute all instructions
supported by the processor. Normally, the operating system and low-level device drivers
operate in this mode.

User Mode

User mode restricts access to some registers and instructions. Normally, application
programs operate in this mode.
Address Translation Modes
The PowerPC 405 also supports two modes of address translation: real and virtual.