Digi NS9215 - Manual (Page 118)

W O R K I N G W I T H T H E C P U
MemoryManagement Unit (MMU)
118 Hardware Reference NS9215
Translation
sequence for tiny
page references
Page translation involves one additional step beyond that of a section translation.
The first-level descriptor is the fine page table descriptor; this points to the first-
level descriptor.
Note:
The domain specified in the first-level description and access permissions
specified in the first-level description together determine whether the access
has permissions to proceed. See “Domain access control” on page 121 for
more information.
Subpages
You can define access permissions for subpages of small and large pages. If, during a
page table walk, a small or large page has a different subpage permission, only the
subpage being accessed is written into the TLB. For example, a 16 KB (large page)
subpage entry is written into the TLB if the subpage permission differs, and a 64 KB
entry is put in the TLB if the subpage permissions are identical.
31 14 13 0
Translation base
1
Translation table base
31 14 13 0
Translation base
2
Table index 0 0
31 20 19 0
Table index Page index
First-level descriptor
31 0
Fine page table base address
2
1 1
1 3 4 5
Domain 1
31 0
Fine page table base address
Level two
table index
10 9
Modified virtual address
8 11 12
1 2 11 12
31 10 9 6 5 4 3 2 1 0
0 0 L2 table index
1 1 B C AP Page base address
Page base address
31 0 10 9
Page index
Physical address
Second-level descriptor