Translation For A Virtual Memory Section; Second-Level Translation Tables - Texas Instruments OMAP5910 Reference Manual

6.2.5.2 Translating Sections
Figure 39.

Translation for a Virtual Memory Section

31
Section base address
31
Section base address
Legend: AP = Access Permissions: 00 or 01 = no access, 10 = read only, 11 = full access; X = don't care
6.2.6

Second-Level Translation Tables

SPRU890A
When the first-level descriptor contains a pointer to a section in physical
memory, the section base address contained in the descriptor is used to
calculate the physical memory address for the original DSP virtual address
(Figure 39).
20 19
20 19
23
1st level
table index
20 19
Once the physical address is known, the data is accessed from physical
memory, assuming the AP bits provide the correct access permissions.
First-level descriptors can provide a pointer to the base address of a
second-level translation table. Second-level translation tables are used when
a granularity smaller than a section is required.
There are two types of second-level translation tables:
Coarse page tables with 256 entries.
-
Descriptors for large and small pages can be used with coarse page
tables.
Fine page tables with 1024 entries.
-
Descriptors for large, small, and tiny pages can be used with fine page
tables.
The type of second-level translation table used depends on the system
requirements. Fine page tables provide a finer granularity, plus they support
all three page sizes; however, they require more space in memory. Coarse
page tables require less space; however, they do not support tiny pages.
First-level descriptor contents
12 11 10 9
X AP
Section index
Section index
DSP Memory Management Unit
2 1
X 1
DSP virtual address
Physical memory address
DSP Subsystem
0
0
0
0
87