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User’s Manual
IBM PowerPC 750GX and 750GL RISC Microprocessor
gx_05.fm.(1.2)
March 27, 2006
Memory Management
Page 187 of 377
When the processor generates an access, and the corresponding address-translation-enable bit in the MSR
is cleared, the resulting physical address is identical to the effective address, and all other translation mecha-
nisms are ignored. Instruction address translation and data address translation are enabled by setting
MSR[IR] and MSR[DR], respectively.
5.1.4 Memory-Protection Facilities
In addition to the translation of effective addresses to physical addresses, the MMUs provide access protec-
tion of supervisor areas from user access and can designate areas of memory as read-only, as well as no-
execute or guarded. Table 5-2 on page 188 shows the protection options supported by the MMUs for pages.
Figure 5-4. Address-Translation Types
(T = 1)
Physical Address
0 31
(T = 0)
0
Effective Address
0
Virtual Address
Segment Descriptor
Located
Match with BAT
Registers
Look Up in
Page Table
Address Translation Disabled
Page Address
Translation
Direct-Store Interface
Translation
(MSR[IR] = 0, or MSR[DR] = 0)
Real Addressing Mode
Effective Address = Physical Address
(See Section 5.2 on page 195)
Block Address Translation
(See Section 5.3 on page 196)
DSI/ISI Exception
0 31 0 31
Physical AddressPhysical Address