Digi NS9750 User Manual
Page 110
M e m o r y M a n a g e m e n t U n i t ( M M U )
8 6
N S 9 7 5 0 H a r d w a r e R e f e r e n c e
Section descriptor
A section descriptor provides the base address of a 1 MB block of memory. Figure 28
shows the section descriptor format. Table 34 describes the section descriptor bits.
Figure 28: Section descriptor
[1:0]
[1:0]
[1:0]
These bits indicate the page size and validity, and are
interpreted as shown in Table 33, “Interpreting first-level
descriptor bits [1:0],” on page 86.
Value
Meaning
Description
0 0
Invalid
Generates a section translation fault.
0 1
Coarse page table
Indicates that this is a coarse page table descriptor.
1 0
Section
Indicates that this is a section descriptor.
1 1
Fine page table
Indicates that this is a fine page table descriptor.
Table 33: Interpreting first-level descriptor bits [1:0]
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.
Table 34: Section descriptor bits
Bits
Section
Coarse
Fine
Description
Table 32: Priority encoding of fault status
Section base address
SBZ
S
B
Z
AP
Domain
1
1
0
C
B
1
0
2
3
4
5
8
9
10
11
12
19
20
31