Digi NS9215 User Manual
Page 114
W O R K I N G W I T H T H E C P U
MemoryManagement Unit (MMU)
114
Hardware Reference NS9215
Second-level
descriptor
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.
Second-level
descriptor format
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.
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
Section index
Section first-level descriptor
31
20 19
0
Section base address
2
0 1
1
3
4
5
SBZ
Domain
AP
1 C B
0
31
20 19
0
Section base address
Physical address
Section index
8
31
16 15
12 11 10
9
8
0
1
2
3
4
5
0
0
0
0
1
1
1
1
C
B
AP0
Large page base address
Small page base address
Tiny page base address
7
6
C
C
B
B
AP0
AP
AP1
AP1
AP2
AP2
AP3
AP3
Fault
Large page
Small page
Tiny page