Digi NS9215 User Manual
Page 110
W O R K I N G W I T H T H E C P U
MemoryManagement Unit (MMU)
110
Hardware Reference NS9215
First-level fetch
concatenation and
address
This address selects a 4-byte translation table entry. This is a first-level descriptor
for either a section or a page.
First-level
descriptor
The first-level descriptor returned is a section description, a coarse page table
descriptor, a fine page table descriptor, or is invalid. This is the format of a first-
level descriptor.
A section descriptor provides the base address of a 1 MB block of memory.
Page table
descriptors
The page table descriptors provide the base address of a page table that contains
second-level descriptors. There are two page-table sizes:
Coarse page tables, which have 256 entries and split the 1 MB that the table
describes into 4 KB blocks.
Fine page tables, which have 1024 entries and split the 1 MB that the table
describes into 1 KB blocks.
Modified virtual address
31
20 19
0
Table index
Translation table base
31
14 13
0
Translation base
31
14 13
0
Translation base
Table index
0
0
1
2
31
0
First-level descriptor
31
20 19
12 11 10
9
8
0
1
2
3
4
5
0
0
0
0
1
1
1
1
1
1
1
C
B
Domain
Domain
Domain
AP
Coarse page table base address
Section base address
Fine page table base address
Fault
Coarse page table
Section
Fine page table