Digi NS9215 Second-level descriptor Second-level descriptor format, Second-level descriptor pages

Models: NS9215

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

MemoryManagement Unit (MMU)

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Table index

Section index

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Translation table base

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Section first-level descriptor

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Section base address

 

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Physical address

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Section base address

Section index

Second-level descriptor

Second-level descriptor format

The base address of the page table to be used is determined by the descriptor returned (if any) from a first-level fetch — either a coarse page table descriptor or a fine page table descriptor. The page table is then accessed and a second-level descriptor returned.

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Large page

Large page base address

 

 

 

AP3

AP2

AP1

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Small page

Small page base address

 

 

 

AP3

AP2

AP1

AP0

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Tiny page

Tiny page base address

 

 

 

 

 

 

 

 

 

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Second-level descriptor pages

A second-level descriptor defines a tiny, small, or large page descriptor, or is invalid:

A large page descriptor provides the base address of a 64 KB block of memory. A small page descriptor provides the base address of a 4 KB block of memory.

114Hardware Reference NS9215

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Digi NS9215 manual Second-level descriptor Second-level descriptor format, Second-level descriptor pages