Atmel ARM-Based Evaluation Kit AT91SAM9N12-EK AT91SAM9N12-EK Ficha De Dados
Códigos do produto
AT91SAM9N12-EK
Memory Management Unit
ARM DDI0198D
Copyright © 2001-2003 ARM Limited. All rights reserved.
3-15
Figure 3-9 Second-level descriptor
A second-level descriptor defines a tiny, a small, or a large page descriptor, or is invalid:
•
a large page descriptor provides the base address of a 64KB block of memory
•
a small page descriptor provides the base address of a 4KB block of memory
•
a tiny page descriptor provides the base address of a 1KB block of memory.
Coarse page tables provide base addresses for either small or large pages. Large page
descriptors must be repeated in 16 consecutive entries. Small page descriptors must be
repeated in each consecutive entry.
descriptors must be repeated in 16 consecutive entries. Small page descriptors must be
repeated in each consecutive entry.
Fine page tables provide base addresses for large, small, or tiny pages. Large page
descriptors must be repeated in 64 consecutive entries. Small page descriptors must be
repeated in four consecutive entries and tiny page descriptors must be repeated in each
consecutive entry.
descriptors must be repeated in 64 consecutive entries. Small page descriptors must be
repeated in four consecutive entries and tiny page descriptors must be repeated in each
consecutive entry.
Second-level descriptor bit assignments are described in Table 3-7.
31
16 15
12 11 10 9 8 7 6 5 4 3 2 1 0
0 0
Large page base address
AP3 AP2 AP1 AP0 C B 0 1
Small page base address
AP3 AP2 AP1 AP0 C B 1 0
Tiny page base address
AP C B 1 1
Fault
Large page
Small page
Tiny page
Table 3-7 Second-level descriptor bits
Bits
Description
Large
Small
Tiny
[31:16]
[31:12]
[31:10]
These bits form the corresponding bits of the physical
address.
address.
[15:12]
-
[9:6]
Should Be Zero.