IBM POWERPC 750GL - Manual (Page 199)

User’s Manual
IBM PowerPC 750GX and 750GL RISC Microprocessor
gx_05.fm.(1.2)
March 27, 2006 Memory Management
Page 199 of 377
For more information, see “Page History Recording” in Chapter 7, “Memory Management,” of the PowerPC
Microprocessor Family: The Programming Environments Manual.
5.4.2 Page Memory Protection
The 750GX implements page memory protection as it is defined in Chapter 7, “Memory Management,” in the
PowerPC Microprocessor Family: The Programming Environments Manual.
5.4.3 TLB Description
The 750GX implements separate 128-entry data and instruction TLBs to maximize performance. This section
describes the hardware resources provided in the 750GX to facilitate page-address translation. Note that the
architecture does not specify the hardware implementation of the MMU, and while this description applies to
the 750GX, it does not necessarily apply to other PowerPC processors.
5.4.3.1 TLB Organization
Because the 750GX has two MMUs (IMMU and DMMU) that operate in parallel, some of the MMU resources
are shared, and some are actually duplicated (shadowed) in each MMU to maximize performance. For
example, although the architecture defines a single set of Segment Registers for the MMU, the 750GX main-
tains two identical sets of Segment Registers, one for the IMMU and one for the DMMU. When an instruction
that updates the Segment Register executes, the 750GX automatically updates both sets.
4
Out-of-order store operation. Required by the sequential
execution model in the absence of system-caused or
imprecise exceptions, or of floating-point assist exception
for instructions that would cause no other kind of precise
exception.
Maybe
1
No No No
5 All other out-of-order store operations Maybe 1 No Maybe 1 No
6 Zero-length load (lswx) Maybe No No No
7 Zero-length store (stswx) Maybe
1
No Maybe
1
No
8 Store conditional (stwcx.) that does not store Maybe
1
Yes Maybe
1
Yes
9 In-order instruction fetch Yes Yes No No
10 Load instruction or eciwx Yes Yes No No
11 Store instruction, ecowx, or dcbz instruction Yes Yes Yes Yes
12
Instruction Cache Block Invalidate (icbi), dcbt, or dcbtst
instruction
Maybe No No No
13
Data Cache Block Store (dcbst) or Data Cache Block
Flush (dcbf) instruction
Maybe Yes No No
14 Data Cache Block Invalidate (dcbi) instruction Maybe 1 Yes Maybe 1 Yes
Note:
1 If C is set, R is guaranteed to be set also.
Table 5-8. Model for Guaranteed R and C Bit Settings (Page 2 of 2)
Priority Scenario
Causes Setting of R Bit Causes Setting of C Bit
OEA 750GX OEA 750GX