AVR32AP datasheet(53/181 Pages) ATMEL

53 / 181 page

32001A–AVR32–06/06

AVR32

4.2.2.2

TLB Entry Register Low Part - TLBELO

The content of the TLBEHI and TLBELO registers is loaded into the TLB when the tlbw instruc-

tion is executed. None of the fields in TLBELO are altered by hardware. The TLBELO register

consists of the following fields:

• PFN - Physical Frame Number to which the VPN is mapped. This field contains 22 bits, but

the number of bits used depends on the page size. A page size of 1 Kb requires 22 bits, while

larger page sizes require fewer bits. When preparing to write an entry into the TLB, the

physical frame number of the entry to write should be written into PFN.

• C - Cacheable. Set if the page is cacheable, cleared otherwise.

• G - Global bit used in the address comparison in the TLB lookup. If the MMU is operating in

the Private Virtual Memory mode and the G bit is set, the ASID won’t be used in the TLB

lookup.

• B - Bufferable. Set if the page is bufferable, cleared otherwise.

• AP - Access permissions specifying the privilege requirements to access the page. The

following permissions can be set, see Table 4-2:

• SZ - Size of the page. The following page sizes are provided, see Table 4-3:

• D - Dirty bit. Set if the page has been written to, cleared otherwise. If the memory access is a

store and the D bit is cleared, an Initial Page Write exception is raised.

• W - Write through. If set, a write-through cache update policy should be used. Write-back

should be used otherwise. The bit is ignored if the cache only supports write-through or write-

back.

Table 4-2.

Access permissions implied by the AP bits

AP[2:0]

Privileged mode

Unprivileged mode

000

Read

None

001

Read / Execute

None

010

Read / Write

None

011

Read / Write / Execute

None

100

Read

101

Read / Execute

110

Read / Write

111

Read / Write / Execute

Table 4-3.

Page sizes implied by the SZ bits

SZ[1:0]

Page size

Bits used in VPN

Bits used in PFN

1 Kb

TLBEHI[31:10]

TLBELO[31:10]

4 Kb

TLBEHI[31:12]

TLBELO[31:12]

64 Kb

TLBEHI[31:16]

TLBELO[31:16]

1 Mb

TLBEHI[31:20]

TLBELO[31:20]

AVR32AP Datasheet(PDF) 53 Page - ATMEL Corporation

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