Second-Level Descriptor Format Based On Two Least-Significant Bits - Texas Instruments OMAP5910 Reference Manual

DSP Memory Management Unit
6.2.6.1 Second-Level Descriptors
Figure 40.

Second-Level Descriptor Format Based on Two Least-Significant Bits

Fault
31
Pointer to large page
31
Large page base address
Pointer to small page
31
Small page base address
Pointer to tiny page
31
Legend: AP = Access Permissions: 00 or 01 = no access, 10 = read only, 11 = full access; X = don't care
88 DSP Subsystem
Both types of page tables contain second-level descriptors which provide the
translation information for a large page, a small page, or a tiny page. Note that
the format of the second-level descriptor is the same regardless of the type of
second-level page table in which it is used. The type of the page table,
however, determines the total number of descriptors needed.
Second-level descriptors provide all the necessary information for the
translation of a large, small, or tiny page. The descriptor can also indicate that
a fault error must be generated if the page is accessed in virtual memory,
similar to first-level section descriptors.
As with first-level descriptors, the least-significant two bits of the second-level
descriptor contents determine the type of information contained in the
descriptor. Figure 40 shows how the contents of the second-level descriptor
are interpreted based on the two least-significant bits. Table 20 further
explains the meaning of each combination.
Tiny page base address
X
16 15
X
12 11
10 9
2 1
0
6 5 4 3 2 1
AP X 0
6 5 4 3 2 1
1
X
AP X
6 5 4 3 2 1
X AP X
1
SPRU890A
0
0
0
1
0
0
0
1