Epson ARM.POWERED ARM720T - Manual (Page 110)

7: Memory Management Unit
7-14 EPSON ARM720T CORE CPU MANUAL
7.3.11 Translating tiny page references
Figure 7-12 shows the complete translation sequence for a 1KB tiny page.
Figure 7-12 Tiny page translation from a fine page table
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.
Note:
The domain specified in the level one description and access permissions specified
in the level one description together determine whether the access has permissions
to proceed. See section Domain access control on page 7-17 for details.
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.
31 14 13 0
Translation base
31 14 13 2 1 0
0 0 Table index Translation base
Modified virtual address
Translation table base
31 20 19 0
Table index Page index
Level one descriptor
Physical address
31 0
Fine page table base address Domain 1 1
2 1 3 4 5 8 9 11
Level 2
table index
10 9
31 0
Page index Page base address
Level two descriptor
31 0
Fine page table base address L2 table index 0
2 1
31 0
Page base address
1
0
ap 1 1 C B
1 2 3 4 5 6 9 10
12
11 12
9 10