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3- 18 M68040 USER'S MANUAL MOTOROLA
ROOT-LEVEL
TABLES
POINTER-LEVEL
TABLES
PAGE-LEVEL
TABLES
0111011001010100001XXXXXXXXXXXXX
ROOT INDEX POINTER INDEX PAGE INDEX PAGE OFFSET
LOGICAL ADDRESS
$76543210 =
$3B $15 $01
TABLE ENTRY # =
TABLE $3B TABLE $15
TABLE $00
TABLE $7F TABLE $1F
TABLE $00 TABLE $00
$3B
$EC $54 $04
ADDRESS OFFSET =
$00001800 $00003000
$80000010
$15 $01
ROOT POINTER
TASK A
TASK B
ROOT POINTER
FRAME ADDRESS
Figure 3-14. Translation Table Using Indirect Descriptors
3.2.4.2 TABLE SHARING BETWEEN TASKS. More than one task can share a pointer- or
page-level table by placing a pointer to a shared table in the address translation tables.
The upper (nonshared) tables can contain different write-protected settings, allowing
different tasks to use the memory areas with different write permissions. In Figure 3-15,
two tasks share the memory translated by the table at the pointer table level. Task A
cannot write to the shared area; task B, however, has the W-bit clear in its pointer to the
shared table so that it can read and write the shared area. Also, the shared area appears
at different logical addresses for each task. Figure 3-15 illustrates shared tables in a
translation table structure.
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