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MMU ARM920T PROCESSOR
3-8
LEVEL ONE DESCRIPTOR
The level one descriptor returned is either a section descriptor a coarse page table descriptor, or a fine page table
descriptor. A section descriptor provides the base address of a 1MB block of memory. The page table descriptors
provide the base address of a page table that contains level two descriptors.
There are two sizes of page table:
• coarse page tables have 256 entries, splitting the 1MB the table describes into 4KB blocks
• fine page tables have 1024 entries, splitting the 1MB the table describes into 1KB blocks
31 19 111220 8 4 3 010 9 5
Domain
0
Coarse page table base address
1AP
Section base address
1
0
12
10
01
11
C B
Domain
DomainFine page table base address
Fault
Coarse page table
Section
Fine page table
1
Figure 3-4. Level One Descriptors
The two least significant bits indicate the descriptor type
Table 3-2. Interpreting Level One Descriptor Bits [1:0]
Value Meaning Notes
00 Invalid Generates a section translation fault.
01 Coarse page table Indicates that this is a coarse page table descriptor.
10 Section Indicates that this is a section descriptor.
11 Fine page table Indicates that this is a fine page table descriptor.