MPU Memory Management Unit
2-32
2.7.6.3
Level 1 Descriptor
The level 1 descriptor returned is either a coarse or fine page table descriptor
or a section descriptor. Its format varies accordingly, as shown in Figure 2–13.
Figure 2–13. Level 1 Descriptors
Fault
Coarse
Page
Section
Fine
Page
Domain
AP
1
C B
0
31
2019
12 11 10 9 8
5
4
3
2 1
Domain
Domain
1
1
0
0
0
1
1
0
1
1
Coarse Page Table Base Address
Section Base Address
Fine Page Table Base Address
Note:
Bits in gray areas are ignored. They must be written to as 0. The two least significant bits indicate the descriptor type and
validity and are interpreted as shown below.
Table 2–17. Level 1 Fine Page Table Descriptor
Bit
Name
Function
31–12
FINE_PG_BASE
Base address used to access the fine page table entry. The fine page
table index selecting an entry is derived from the virtual address as
illustrated in Figure 2–16, Tiny Page Translation.
11–9
RESERVED
Reserved. Must be written as 0.
8–5
DOMAIN
Specify which one of the sixteen domains (held in the domain access
control register) contains the primary access controls.
4
RESERVED
Reserved. Must be written to as 1 for backward compatibility.
3–0
RESERVED
Reserved. Must always be written as 0.
1–0
RESERVED
Reserved. Must always be written as 1.
If a page table descriptor is returned from the level 1 fetch (Bit 0 = 1), a level
2 fetch is initiated.
Table 2–18. Interpreting Level 1 Descriptor Bits 1–0
Value
Meaning
Notes
00
Invalid
Generates a section translation fault
01
Coarse
Indicates a coarse page descriptor
10
Section
Indicates a section descriptor
11
Fine
Indicates a fine page descriptor