Digi NS9215 manual 113

Models: NS9215

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Fine page table descriptor format

Fine page table descriptor bit description

Translating section references

WO R K I N G W I T H T H E C P U

. .

 

MemoryManagement Unit (MMU)..

 

.

page tables have 1024 entries, splitting the 1 MB that the table describes into 1 KB blocks. The next two sections show the format of a fine page table descriptor and define the fine page table descriptor bit assignments.

Note: If a fine page table descriptor is returned from the first-level fetch, a second-level fetch is initiated.

31

12

11

9

8

5

4

3

2

1

0

 

 

 

 

 

 

 

 

 

 

Fine page table base address

 

 

SBZ

 

Domain

1

SBZ

1

1

 

 

 

 

 

 

 

 

 

 

 

Bits

Description

 

 

[31:12]

Forms the base for referencing the second-level descriptor (the fine page table index for

 

the entry is derived from the MVA).

 

 

[11:9]

Always written as 0.

 

 

[8:5]

Specifies one of the 16 possible domains (held in the Domain Access Control register)

 

that contain primary access controls.

 

 

4

Always written as 1.

 

 

[3:2}

Always written as 0.

 

 

[1:0]

Must be 11 to indicate a fine page table descriptor.

 

 

This figure illustrates the complete section translation sequence.

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Page 113
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Digi NS9215 manual 113