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A level two descriptor defines a tiny, a small, or a large page descriptor, or is invalid:
•
a large page descriptor provides the base address of a 64KB block of memory
•
a small page descriptor provides the base address of a 4KB block of memory
•
a tiny page descriptor provides the base address of a 1KB block of memory.
Coarse page tables provide base addresses for either small or large pages. Large page
descriptors must be repeated in 16 consecutive entries. Small page descriptors must be
repeated in each consecutive entry.
Fine page tables provide base addresses for large, small, or tiny pages. Large page descriptors
must be repeated in 64 consecutive entries. Small page descriptors must be repeated in four
consecutive entries and tiny page descriptors must be repeated in each consecutive entry.
Level two descriptor bit assignments are described in Table 7-7.
Bits
Large
31:16
15:12
11:4
3:2
1:0
The two least significant bits of the level two descriptor indicate the descriptor type as shown
in Table 7-8.
Value
0 0
0 1
1 0
1 1
Tiny pages do not support subpage permissions and therefore only have one set of
Note:
access permission bits.
ARM720T CORE CPU MANUAL
Table 7-7 Level two descriptor bits
Description
Small
Tiny
31:12
31:10
These bits form the corresponding bits of the
physical address
-
9:6
Should Be Zero
11:4
5:4
Access permission bits. Domain access control
on page 7-17 and Fault checking sequence on
page 7-19 show how to interpret the access
permission bits
3:2
3:2
These bits, C and B, indicate whether the area of
memory mapped by this page is treated as
cachable or noncachable, and bufferable or
nonbufferable. (The system is always
write-through.)
1:0
1:0
These bits indicate the page size and validity and
are interpreted as shown in Table 7-8
Table 7-8 Interpreting page table entry bits [1:0]
Meaning
Description
Invalid
Generates a page translation fault
Large page
Indicates that this is a 64KB page
Small page
Indicates that this is a 4KB page
Tiny page
Indicates that this is a 1KB page
EPSON
7: Memory Management Unit
7-11
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