SH7713 datasheet(236/904 Pages) RENESAS

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Section 5 Memory Management Unit (MMU)

Rev.1.50 Aug. 30, 2006 Page 196 of 860

REJ09B0288-0150

Virtual Address

Index

Way 0 to 3

VPN(31-17)

VPN(11-10)

ASID(7-0)

Address Array

Data Array

PPN(28-10) PR(1-0) SZ

Figure 5.9 TLB Indexing (IX = 0)

5.3.3

TLB Address Comparison

The results of address comparison determine whether a specific virtual page number is registered

in the TLB. The virtual page number of the virtual address that accesses external memory is

compared to the virtual page number of the indexed TLB entry. The ASID within the PTEH is

compared to the ASID of the indexed TLB entry. All four ways are searched simultaneously. If

the compared values match, and the indexed TLB entry is valid (V bit

= 1), the hit is registered.

It is necessary to have software ensure that TLB hits do not occur simultaneously in more than one

way, as hardware operation is not guaranteed if this occurs. An example of setting which causes

TLB hits to occur simultaneously in more than one way is described below. It is necessary to

ensure that this kind of setting is not made by software.

1. If there are two identical TLB entries with the same VPN and a setting is made such that a

TLB hit is made only by a process with ASID = H'FF when one is in the shared state (SH = 1)

and the other in the non-shared state (SH = 0), then if the ASID in PTEH is set to H'FF, there is

a possibility of simultaneous TLB hits in both these ways.

2. If several entries which have different ASID with the same VPN are registered in single virtual

memory mode, there is the possibility of simultaneous TLB hits in more than one way when

accessing the corresponding page in privileged mode. Several entries with the same VPN must

not be registered in single virtual memory mode.

3. There is the possibility of simultaneous TLB hits in more than one way. These hits may occur

depending on the contents of ASID in PTEH when a page to which SH is set 1 is registered in

the TLB in index mode (MMUCR.IX = 1). Therefore a page to which SH is set 1 must not be

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