MC68LC040RC25A Datasheet, PDF (67/442 Pages) Freescale Semiconductor, Inc – M68040 Users Manual

Freescale Semiconductor, Inc.
LOGICAL ADDRESS
ROOT INDEX
POINTER INDEX PAGE INDEX
PAGE OFFSET
$76543210 = _{0 1 1 1 0 1 1 0 0 1 0 1 0 1 0 0 0 0 1 X X X X X X X X X X X X X}
TABLE ENTRY # =
$3B
ADDRESS OFFSET =
$EC
$15
$01
$54
$04
TABLE $00
TABLE $00
TABLE $00
TASK A
ROOT POINTER
$3B $00001800
TABLE $3B
$15 $00003000
TABLE $15
$01 $80000010
TASK B
ROOT POINTER
TABLE $7F
TABLE $1F
FRAME ADDRESS
ROOT-LEVEL
TABLES
POINTER-LEVEL
TABLES
PAGE-LEVEL
TABLES
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.
3-18
M68040 USER'S MANUAL
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