MC68LC040RC25A Datasheet, PDF (66/442 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
SUPERVISOR
SRP
MODE
$3B $00001800
TABLE $3B
$15 $00003000
TABLE $15
$01 FRAME ADDRESS
TABLE $7F
TABLE $1F
ROOT LEVEL
TABLES
POINTER LEVEL
TABLES
Figure 3-13. Example Translation Table
PAGE LEVEL
TABLES
Using the indirection capability, single entries or entire tables can be shared between
multiple tasks. Figure 3-14 illustrates two tasks sharing a page using indirect descriptors.
When the M68040 has completed a normal table search, it examines the PDT field of the
last entry fetched from the page tables. If the PDT field contains an indirect ($2) encoding,
it indicates that the address contained in the highest order 30 bits of the descriptor is a
pointer to the page descriptor that is to be used to map the logical address. The processor
then fetches the page descriptor from this address and uses the physical address field of
the page descriptor as the physical mapping for the logical address.
The page descriptor located at the address given by the indirect descriptor must not have
a PDT field with an indirect encoding (it must be either a resident descriptor or invalid).
Otherwise, the descriptor is treated as invalid, and the M68040 creates an ATC entry with
a signaled error condition (R-bit in MMUSR is clear).
MOTOROLA
M68040 USER'S MANUAL
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