Digi NS9215, Hardware Reference Manual, Page: 110 / 517

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