Determining Virtual Address Tags For Tlb Cam Entries - Texas Instruments OMAP5910 Reference Manual

Figure 27.

Determining Virtual Address Tags for TLB CAM Entries

Section
23 20
Section base address
Large page
23
Large page base address
Small page
23
Small page base address
Tiny page
23
Tiny page base address
SPRU890A
The virtual address tag is a 14-bit field derived from the virtual address of the
memory request being processed. Not all the bits in the virtual address tag are
needed for translation. Instead, the size of the memory block described by the
entry determines the number of bits used. For example, only bits 13:10 of the
virtual address tag are used for a section. When writing entries to the TLB,
unused bits in the virtual address tags must always be kept as zeros. The read
value of unused bits is not predictable. Figure 27 shows how to determine the
virtual address tag from the DSP virtual address. Note that a section
corresponds to 1 Mbytes of memory, a large page corresponds to 64 Kbytes
of memory, a small page corresponds to 4 Kbytes of memory, and a tiny page
corresponds to 1 Kbyte of memory.
19
13
16 15
13
12
13
Small page base address
13
The valid parameter of the TLB entry value specifies whether an entry is valid.
The table walking logic can overwrite non-valid entries. The table walking logic
first attempts to fill all non-protected, non-valid entries before replacing valid
entries.
Page index
10 9
0 0 0 0 0 0 0 0 0 0
Page index
6 5
0 0 0 0 0 0
11
Page index
10 9
Page index
Tiny page base address
DSP Memory Management Unit
0
DSP virtual address
0
Virtual address tag
0
DSP virtual address
0
Virtual address tag
0
DSP virtual address
2 1 0
0 0
Virtual address tag
0
DSP virtual address
0
Virtual address tag
DSP Subsystem 71