First-Level Descriptor Format Based On Two Least-Significant Bits; First−Level Descriptor Contents - Texas Instruments OMAP5910 Reference Manual

DSP Memory Management Unit
Figure 38.

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

Fault
31
Pointer to course page table
31
Course page table base address
Pointer to section in physical memory
31
Section base address
Pointer to fine page table
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
Table 19. First−Level Descriptor Contents
Least-Significant
Two Bits of Des-
criptor Contents
00b Any access to this section in virtual memory will generate a fault error. As described in
section 6.2.7, the fault error must be addressed by the MPU core. Until the error is
cleared, the DSP EMIF will be stalled, therefore stalling the original requestor (either
the DSP core or DMA).
01b The descriptor contains the base address for a coarse page table. The coarse page
table base address is used in conjunction with a second-level table index to determine
the address of a second−level descriptor. The second-level descriptor provides the
translation information for either a large page or a small page. Section 6.2.6.5 de-
scribes coarse page tables.
10b The descriptor contains the base address for a section in physical memory. The section
base address and the section index (bits 19−0 of the virtual address) are used
determine the physical memory address. Section 6.2.5.2 describes this process.
11b The descriptor contains the base address for a fine page table. The fine page table
base address is used in conjunction with a second-level table index to determine the
address of a second-level descriptor. The second-level descriptor provides the
translation information for a large page, a small page, or a tiny page. Section 6.2.6.6
describes fine page tables.
86 DSP Subsystem
X
20 19
X
12 11
Descriptor Contents Meaning
10 9
X
11 10 9
AP X
X
0
2 1
0 0
2 1 0
0 1
2 1 0
1 0
2 1 0
1 1
SPRU890A