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User’s Manual
IBM PowerPC 750GX and 750GL RISC Microprocessor
Memory Management
Page 194 of 377
gx_05.fm.(1.2)
March 27, 2006
5.1.8 MMU Instructions and Register Summary
The MMU instructions and registers allow the operating system to set up the block-address-translation areas
and the page tables in memory.
Notes:
• Because the implementation of TLBs is optional, the instructions that refer to these structures are also
optional. However, as these structures serve as caches of the page table, the architecture specifies a
software protocol for maintaining coherency between these caches and the tables in memory whenever
the tables in memory are modified. When the tables in memory are changed, the operating system
purges these caches of the corresponding entries, allowing the translation caching mechanism to refetch
from the tables when the corresponding entries are required.
• Also note that the 750GX implements all TLB-related instructions except TLB Invalidate All (tlbia), which
is treated as an illegal instruction.
Because the MMU specification for PowerPC processors is so flexible, it is recommended that the software
that uses these instructions and registers be encapsulated into subroutines to minimize the impact of
migrating across the family of implementations.
Table 5-5 summarizes the 750GX’s instructions that specifically control the MMU. For more detailed informa-
tion about the instructions, see Chapter 2, Programming Model, on page 57 and Chapter 8, “Instruction Set,”
in the PowerPC Microprocessor Family: The Programming Environments Manual
.
eciwx or ecowx attempted when external
control facility disabled
eciwx or ecowx attempted with EAR[E] = 0
DSI exception
DSISR[11] = 1
Load Multiple Word (lmw), Store Multiple
Word (stmw), lswi, Load String Word
Immediate (lswx), Store String Word Imme-
diate (stswi), or Store String Word Indexed
x-form (stswx) instruction attempted in little-
endian mode
lmw, stmw, lswi, lswx, stswi, or stswx
instruction attempted while MSR[LE] = 1
Alignment exception
Operand misalignment
Translation enabled and a floating-point
load/store, stmw, stwcx., lmw, lwarx,
eciwx, or ecowx instruction operand is not
word-aligned
Alignment exception (some of these cases
are implementation-specific)
Table 5-5. 750GX Microprocessor Instruction Summary—Control MMUs (Page 1 of 2)
Instruction Description
mtsr SR,rS
Move-to Segment Register
SR[SR#]
← rS
mtsrin rS,rB
Move-to Segment Register Indirect
SR[rB[0–3]]
←rS
mfsr rD,SR
Move-from Segment Register
rD
←SR[SR#]
mfsrin rD,rB
Move-from Segment Register Indirect
rD
←SR[rB[0–3]]
Table 5-4. Other MMU Exception Conditions for the 750GX Processor (Page 2 of 2)
Condition Description Exception