Epson ARM720T Manuel D’Utilisation
7: Memory Management Unit
7-10
EPSON
ARM720T CORE CPU MANUAL
7.3.7
Translating section references
Figure 7-8 shows the complete section translation sequence.
Figure 7-8 Section translation
Note:
You must check access permissions contained in the level one descriptor before
generating the physical address.
7.3.8
Level two descriptor
If the level one fetch returns either a coarse page table descriptor or a fine page table
descriptor, this provides the base address of the page table to be used. The page table is then
accessed and a level two descriptor is returned. Figure 7-9 shows the format of level two
descriptors.
Figure 7-9 Level two descriptor
31
14 13
0
Translation base
31
14 13
2 1 0
0 0
Table index
Translation base
Modified virtual address
Translation table base
31
20 19
0
Table index
Section index
31
20 19
0
Section index
Section base address
Section level one descriptor
Physical address
31
20 19
0
Section base address
AP
Domain 1 C B 1 0
2 1
3
4
5
8
9
10
11
12
31
12 11 10 9 8
5 4 3 2 1 0
0 0
Large page base address
0 1
Small page base address
C B 1 0
Tiny page base address
1 1
Fault
Large page
Small page
Tiny page
7 6
16 15
B
C
C B
ap0
ap0
ap
ap1
ap2
ap3
ap1
ap2
ap3