Digi NS9750 - 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