mc68ec060 Freescale Semiconductor, Inc, mc68ec060 Datasheet - Page 85

• Manufacturer Part Number: mc68ec060
• Description: Mc68060 Superscalar 68k Microprocessor Including The Lc060 And Ec060
• Manufacturer: Freescale Semiconductor, Inc

Memory Management Unit
4.2.4 Variations in Translation Table Structure
Several aspects of the MMU translation table structure are software configurable, allowing
the system designer flexibility to optimize the performance of the MMUs for a particular sys-
tem. The following paragraphs discuss the variations of the translation table structure.
4.2.4.1 INDIRECT ACTION. The MC68060 provides the ability to replace an entry in a page
table with a pointer to an alternate entry. The indirection capability allows multiple tasks to
share a physical page while maintaining only a single set of history information for the page
(i.e., the modified indication is maintained only in the single descriptor). The indirection
capability also allows the page frame to appear at arbitrarily different addresses in the logical
address spaces of each task.
Using the indirection capability, single entries or entire tables can be shared between multi-
ple tasks. Figure 4-13 illustrates two tasks sharing a page using indirect descriptors.
4-16
TASK A
TASK B
ADDRESS OFFSET =
TABLE ENTRY # =
$76543210 =
Figure 4-13. Translation Table Using Indirect Descriptors
ROOT POINTER
ROOT POINTER
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
ROOT INDEX
$EC
$3B
$3B
M68060 USER’S MANUAL
ROOT-LEVEL
POINTER INDEX
TABLE $00
$00001800
TABLES
$15
$54
LOGICAL ADDRESS
PAGE INDEX
$15
$01
$04
POINTER-LEVEL
TABLE $3B
TABLE $00
$00003000
TABLE $7F
TABLES
PAGE OFFSET
$01
FRAME ADDRESS
PAGE-LEVEL
TABLE $15
TABLE $1F
TABLE $00
$80000010
TABLES
MOTOROLA