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Memory Management Unit
9-50
MC68030 USER’S MANUAL
MOTOROLA
The bits in the MMUSR have different meanings for the two kinds of PTEST instructions, as
shown in Table 9-3.
Table 9-3. MMUSR Bit Definitions
MMUSR Bit
Bus Error (B)
PTEST, Level 0
PTEST, Level 1-7
This bit is set if a bus error is
encountered during the table
search for the PTEST instruction.
This bit is set if an index exceeds a
limit during the table search
This bit is set if the S bit of a long (S)
format table descriptor or long
format page descriptor
encountered during the search is
set, and the FC2 bit of the function
code specified by the PTEST
instruction is not equal to one. The
S bit is undefined if the I bit is set.
This bit is set if a descriptor or page
descriptor is encountered with the
WP bit set during the table search.
The W bit is undefined if the I bit is
set.
This bit indicates an invalid
translation. The I bit is set if the DT
field of a table or a page descriptor
encountered during the serach is
set to invalid or if either the B or L
bits of the MMUSR are set during
the table search.
This bit is set if the page descriptor
for the specified address has the
modified bit set. It is undefined if I is
set.
This bit is set to zero.
This bit is set if the bus error bit is
set in the ATC entry for the
specified logical address.
This bit is cleared.
Limit (L)
Supervisor Violation (S)
This bit is cleared
Write Protected (W)
This bit is set if the WP bit of the
ATC entry is set. It is undefined if
the I bit is set
Invalid (I)
This bit indicates an invalid
translation. The I bit is set if the
translation for the specified logical
address is not resident in the ATC
or if the B bit of the corresponding
ATC entry is set.
Modified (M)
This bit is set if the ATC entry
corresponding to the specified
address has the modified bit set. It
is undefined if the I bit is set.
This bit is set if a match occurred in
either (or both) of the transparent
translation registers (TT0 or TT1). If
the T bit is set, all remaining
MMUSR bits are undefined.
This 3-bit field is cleared to zero.
Transparent (T)
Number of Levels (N)
This 3-bit field contains the actual
number of tables accessed during
the search.