Fujitsu Fujitsu SPARC64 V manual TLB Replacement Policy, Automatic TLB Replacement Rule

Models: Fujitsu SPARC64 V

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F.11.10 TLB Replacement Policy

Automatic TLB Replacement Rule

On an automatic replacement write to the TLB, the MMU picks the entry to write according to the following rules:

1.If the following conditions are satisfied—

the new entry maps to an 8-Kbyte or an 4-Mbyte unlocked page

and ASI_MCNTRL.fw_fITLB = 0 for IMMU automatic replacement

and ASI_MCNTRL.fw_fDTLB = 0 for DMMU automatic replacement

—then the replacement is directed to the sTLB (2-way TLB). Otherwise, the replacement occurs in the fully associative TLB (fTLB).

2.If replacement is directed to the 2-way TLB, then the replacement set index is generated from the TLB Tag Access Register: bits 21:13, bits 30:22 or bits 29:22 depending on the page size and MCNTL.RMD for both I-MMU and D-MMU.

3.If replacement is directed to the fully associative TLB (fTLB), then the following alternatives are evaluated:

a.The first invalid entry is replaced (measuring from entry 0). If there is no invalid entry, then

b.the first unused, unlocked (LRU, but clear) entry will be replaced (measuring from entry 0). If there is no unused unlocked entry, then

c.all used bits are reset, and the process is repeated from Step 3b.

If fTLB is the target of the automatic replacement and all entries in the fTLB have their lock bit set, the automatic replacement operation is ignored and the entries in the target fTLB remain unchanged.

Restriction of sTLB Entry Direct Replacement

On SPARC64 V, direct replacement of a specific sTLB entry requires that the stxa instruction to the I/D TLB Data Access Register be designated as follows.

stxa ASI designation:

ASI 5516for sITLB

ASI 5D16for sDTLB

stxa virtual address designation:

VA<17:16> = 1002

: sTLB designation

VA<15> = 0 or 1 : Error injection designation

VA<13> = 0 or 1 : 8-Kbyte or 4-Mbyte page designation

VA<12> = 0 or 1

: sTLB way number

VA<11:3>

: sTLB index number

Release 1.0, 1 July 2002

F. Chapter F Memory Management Unit 105

Page 116
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Fujitsu Fujitsu SPARC64 V manual TLB Replacement Policy, Automatic TLB Replacement Rule