mc68ec060 Freescale Semiconductor, Inc, mc68ec060 Datasheet - Page 88

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

4.2.5 Table Search Accesses
Table search accesses bypass the data cache. No allocation is done and no cache search
is performed. Translation tables must not be placed in copyback space, since the normal
accesses which build the translation tables would be cached and not written to external
memory, but the processor only uses tables in external memory.
During a table search, the U- and M-bits of the table descriptors are examined. For any
access, if the U-bit is not set, the processor sets it using a complete read-modify-write
sequence with the LOCK pin asserted. LOCK is asserted in this case to avoid loss of the
status in certain multiprocessor applications which share translation tables. For a write
access, if the M-bit in the page descriptor is not set, and if the page is not write-protected
(W = 0) and the access is not a supervisor violation (for user accesses, the S-bit of the page
descriptor must be clear), then the M-bit is set using a simple write. The U- and M-bits are
MOTOROLA
ADDRESS OFFSET =
TABLE ENTRY # =
$76543210 =
Figure 4-15. Translation Table with Nonresident Tables
SRP
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
UDT = RESIDENT
UNALLOCATED)
UNALLOCATED)
NONRESIDENT
NONRESIDENT
SUPERVISOR
UDT = INVALID
UDT = INVALID
UDT = INVALID
UDT = INVALID
M68060 USER’S MANUAL
ROOT-LEVEL
(PAGED OR
(PAGED OR
TABLE $00
TABLES
POINTER INDEX
$15
$54
LOGICAL ADDRESS
PAGE INDEX
$15
$01
$04
UDT = RESIDENT
UNALLOCATED)
UNALLOCATED)
POINTER-LEVEL
NONRESIDENT
NONRESIDENT
UDT = INVALID
UDT = INVALID
UDT = INVALID
UDT = INVALID
(PAGED OR
(PAGED OR
TABLE $7F
TABLE $3B
TABLE $00
TABLES
PAGE OFFSET
Memory Management Unit
$01
FRAME ADDRESS
UNALLOCATED)
UNALLOCATED)
NONRESIDENT
NONRESIDENT
PAGE-LEVEL
(PAGED OR
(PAGED OR
TABLE $00
TABLE $1F
TABLE $15
TABLES
4-19