Digi NS9215 - Manual (Page 112)

W O R K I N G W I T H T H E C P U
MemoryManagement Unit (MMU)
112 Hardware Reference NS9215
Section descriptor
bit description
Coarse page table
descriptor
A coarse page table descriptor provides the base address of a page table that
contains second-level descriptors for either large page or small page accesses.
Coarse page tables have 256 entries, splitting the 1 MB that the table describes into
4 KB blocks.
Note:
If a coarse page table descriptor is returned from the first-level fetch, a
second-level fetch is initiated.
Coarse page table
descriptor format
Coarse page table
descriptor bit
description
Fine page table
descriptor
A fine page table descriptor provides the base address of a page table that contains
second-level descriptors for large page, small page, or tiny page accesses. Fine
Bits Description
[31:20] Forms the corresponding bits of the physical address for a section.
[19:12] Always written as 0.
[11:10] Specify the access permissions for this section.
[09] Always written as 0.
[8:5] Specifies one of the 16 possible domains (held in the Domain and Access Control
register) that contain the primary access controls.
4 Should be written as 1, for backwards compatibility.
[3:2] Indicate if the area of memory mapped by this section is treated as writeback cachable,
write-through cachable, noncached buffered, or noncached nonbuffered.
[1:0] Must be 10 to indicate a section descriptor.
Coarse page table base address
S
B
Z
1 0 1
1 0 2 3 4 5 8 9 31
SBZ
10
Domain
Bits Description
[31:10] Forms the base for referencing the second-level descriptor (the coarse page table index
for the entry derived from the MVA).
9 Always written as 0.
[8:5] Specifies one of the 16 possible domains (held in the Domain Access Control registers)
that contain the primary access controls.
4 Always written as 1.
[3:2] Always written as 0.
[1:0] Must be 01 to indicate a coarse page descriptor.