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7: Memory Management Unit
7.3.11
Translating tiny page references
Figure 7-12 shows the complete translation sequence for a 1KB tiny page.
31
Translation base
31
Translation base
31
Fine page table base address
31
Fine page table base address
31
Page base address
31
Page base address
Page translation involves one additional step beyond that of a section translation. The level
one descriptor is the fine page table descriptor and this is used to point to the level one
descriptor.
The domain specified in the level one description and access permissions specified
Note:
in the level one description together determine whether the access has permissions
to proceed. See section
7.3.12
Subpages
You can define access permissions for subpages of small and large pages. If, during a page
walk, a small or large page has a non-identical subpage permission, only the subpage being
accessed is written into the TLB. For example, a 16KB (large page) subpage entry is written
into the TLB if the subpage permission differs, and a 64KB entry is put in the TLB if the
subpage permissions are identical.
When you use subpage permissions, and the page entry then has to be invalidated, you must
invalidate all four subpages separately.
7-14
31
Translation table base
14 13
14 13
Level one descriptor
12
12
Level two descriptor
Physical address
Figure 7-12 Tiny page translation from a fine page table
Domain access control
Modified virtual address
20 19
Table index
table index
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2 1 0
Table index
0 0
11
9
8
5
4
3
2 1
0
Domain 1
1
1
11
2 1
0
L2 table index
0
0
10
9
6
5
4
3
2
1
0
ap
C B
1
1
10
9
0
Page index
on page 7-17 for details.
EPSON
10 9
Level 2
Page index
ARM720T CORE CPU MANUAL
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