Sun Microelectronics
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6. MMU Internal Architecture
TLB Data In register for automatic replacement also uses the Tag Access
register, but typically the value written into the Tag Access register by the
MMU hardware is appropriate.
Note:
Any update to the Tag Access registers immediately affects the data that
is returned from subsequent reads of the Tag Target and TSB Pointer registers.
The TLB Tag Access Registers are defined as follows:
Figure 6-10
I/D MMU TLB Tag Access Registers
I/D VA<63:13>
: The 51-bit virtual page number. Note that writes to this field are
not checked for out-of-range violation, but sign extended based on VA<43>.
Warning –
Stores to the Tag Access registers are not checked for out-of-range
violations. Reads from these registers are sign-extended based on VA<43>.
I/D Context<12:0>
: The 13-bit context identifier. This field reads zero when there
is no associated context with the access.
6.9.8 I-/D-TSB 8 Kb/64 Kb Pointer and Direct Pointer Registers
These registers are provided to help the software determine the location of the
missing or trapping TTE in the software-maintained TSB. The TSB 8 Kb and 64
Kb Pointer registers provide the possible locations of the 8 Kb and 64 Kb TTE, re-
spectively. The Direct Pointer register is mapped by hardware to either the 8 Kb
or 64 Kb Pointer register in the case of a
fast_data_access_protection
exception ac-
cording to the known size of the trapping TTE. In the case of a 512 Kb or 4 Mb
page miss, the Direct Pointer register returns the pointer as if the miss were from
an 8 Kb page.
The TSB Pointer registers are implemented as a re-order of the current data
stored in the Tag Access register and the TSB register. If the Tag Access register or
TSB register is updated through a direct software write (via a STXA instruction),
then the Pointer registers values will be updated as well.
The bit that controls selection of 8K or 64K address formation for the Direct
Pointer register is a state bit in the D-MMU that is updated during a
data_access_protection
exception. It records whether the page that hit in the TLB
was an 64K page or a non-64K page, in which case 8K is assumed.
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0
VA<63:13>
Context<12:0>
13 12
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