Calculating The Descriptor Address In A Fine Page Table - Texas Instruments OMAP5910 Reference Manual

DSP Memory Management Unit
6.2.6.6 Fine Page Tables
Figure 45.

Calculating the Descriptor Address in a Fine Page Table

31
Fine page table base address
31
Fine page table base address
Legend: AP = Access Permissions: 00 or 01 = no access, 10 = read only, 11 = full access; X = don't care
92 DSP Subsystem
As described in section 6.2.2, the TLB can be used to bypass the translation
tables. Using this approach, only one TLB entry is required to translate a large
page.
Fine page tables can be used to map large, small, and tiny pages of virtual
memory to physical memory. The added granularity comes at a cost, because
each fine page table must contain 1024 entries.
Follow these rules when using fine page tables:
The start address of fine tables must be aligned on a 4096-byte boundary;
-
that is, the last 12 bits of its start address must be zeros.
A descriptor for a large page must be repeated 64 times. The repeated
-
descriptor must start at an entry number that is a multiple of 64. As
described in section 6.2.2, only one entry is required in the TLB to translate
a large page.
A descriptor for a small page must be repeated four times. The repeated
-
descriptor must start at an entry number that is a multiple of four. As
described in section 6.2.2, only one entry is required in the TLB to translate
a small page.
The address of the second-level descriptor is determined by using the fine
page table base address (contained in the first-level descriptor) and a
second-level table index. The second-level table index is taken from the DSP
virtual address.
Figure 45 describes how the descriptor address is generated for fine page
tables.
23 20 19
X 2nd level table index
First-level descriptor contents
12 11
X
DSP virtual address
10 9
Second-level descriptor address
12 11
2nd level table index
0
2 1
1 1
0
X
2 1 0
0 0
SPRU890A