Digi NS9750 - Manual (Page 108)

M e m o r y M a n a g e m e n t U n i t ( M M U )
8 4 N S 9 7 5 0 H a r d w a r e R e f e r e n c e
First-level fetch
Bits [31:14] of the TTB register are concatenated with bits [31:20] of the MVA to
produce a 30-bit address.
Figure 26 shows the concatenation and address:
Figure 26: Accessing translation table first-level descriptors
This address selects a 4-byte translation table entry. This is a first-level descriptor for
either a section or a page.
First-level descriptor
The first-level descriptor returned is a section description, a coarse page table
descriptor, a fine page table descriptor, or is invalid. Figure 27 shows the format of a
first-level descriptor.
A section descriptor provides the base address of a 1 MB block of memory.
The page table descriptors provide the base address of a page table that contains
second-level descriptors. There are two page-table sizes:
Coarse page tables, which have 256 entries and split the 1 MB that the
table describes into 4 KB blocks.
Modified virtual address
31 20 19 0
Table index
Translation table base
31 14 13 0
Translation base
31 14 13 0
Translation base Table index 0 0
1 2
31 0
First-level descriptor