Digi NS9750 - Manual (Page 111)

w w w . d i g i e m b e d d e d . c o m 8 7
W o r k i n g w i t h t h e C P U
Coarse page table descriptor
A coarse page table descriptor provides the base address of a page table that
contains second-level descriptors for either large page or small page accesses. Coarse
page tables have 256 entries, splitting the 1 MB that the table describes into 4 KB
blocks. Figure 29 shows the coarse page table descriptor format; Table 35 describes
the coarse page table descriptor bit assignments.
Note:
If a coarse page table descriptor is returned from the first-level fetch, a
second-level fetch is initiated.
Figure 29: Coarse page table descriptor
[8:5] Specifies one of the 16 possible domains (held in the Domain and Access Control register)
that contain the primary access controls.
4 Should be written as 1, for backwards compatibility.
[3:2] Indicate if the area of memory mapped by this section is treated as writeback cachable,
write-through cachable, noncached buffered, or noncached nonbuffered.
[1:0] Must be 10 to indicate a section descriptor.
Bits Description
[31:10] Forms the base for referencing the second-level descriptor (the coarse page table index for
the entry derived from the MVA).
9 Always written as 0.
[8:5] Specifies one of the 16 possible domains (held in the Domain Access Control registers)
that contain the primary access controls.
4 Always written as 1.
[3:2] Always written as 0.
Table 35: Coarse page table descriptor bits
Bits Description
Table 34: Section descriptor bits
Coarse page table base address
S
B
Z
1 0 1
1 0 2 3 4 5 8 9 31
SBZ
10
Domain