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MOTOROLA M68040 USER’S MANUAL 8- 31
Table 8-6. Access Error Stack Frame Combinations
WB1S WB2S WB3S Easy Cleanup Hard Cleanup
Main Case SSW_RW SSW_PUSH 1V 1M16 2V 2M16 3V Data Written Action
All Read
Access Errors
1a
1aNo
No
0
0
X
X
0
0
X
X
0
1
None
WB3D (Note b)
All other read cases are not possible.
Cache Push
Physical Bus
Error c
0
0
0
0
0
Yes
Yes
Yes
Yes
Yes
0
0
0
0
0
X
X
X
X
X
0
0
1
1
1
X
X
0
0
1
0
1
0
1
0
PD3–0
PD3–0, WB3D
PD3–0, WB2D
PD3–0, WB2D, WB3D
PD3–0, ~WB2Dd
(Note b)
Normal Write
Physical bus
Error
0
0
0
0
0
No
No
No
No
No
1
1
1
1
1
0
0
0
0
0
0
0
1
1
1
X
X
0
0
1
0
1
0
1
0
WB1D
WB1D, WB3D
WB1D, WB2D
WB1D, WB2D, WB3D
WB1D, ~WB2Dd
(Note b)
MOVE16
Write Physical
Bus Error
0
0
0
0
0
No
No
No
No
No
1
1
1
1
1
1
1
1
1
1
0
0
1
1
1
X
X
0
0
1
1
0
0
1
0
PD3–0, WB3D
PD3–0
PD3–0, WB2D
PD3–0, WB2D, WB3D
PD3–0, ~WB2Dd
(Note b)
Write Page
Fault
0
0
0
No
No
No
0
0
0
X
X
X
1
1
1
0
0
1
0
1
0
WB2D
WB2D, WB3D
~WB2DdWrite PD3–0
and skipe.
Impossible
Write Cases
0
0
Yes
Don't Care
1
X
X
X
X
X
X
1
X
1
(Note f)
(Note g)
NOTES:
a. The data memory unit stage is tied up until the bus controller passes the read back through the data memory
unit and to the execution stage in the integer unit. Therefore, no pending write is possible in WB1 or WB2.
WB3 could hold a pending write that was deferred due to operand read or was generated after the read.
b. If any kind of access error is reported and if a MOVE16 write is pending in the WB2 stage, then that MOVE16
read must hit in the cache so the MOVE16 can be safely restarted since it has not caused bus cycles that could
retouch peripherals.
c. A cache push physical bus error is normally considered a fatal error. For these cases, the FA field is a physical
address, not a logical address as in the other cases.
d. Indicates that the data should not be written even though the V-bit for it is set (WB2 corresponds to a MOVE16
write).
e. The exception handler must alter the stacked PC to point past the MOVE16 and predecrement and
postincrement address registers.
f. 1V must be 0 for push exceptions.
g. The execution stage does not post a write until the MOVE16 is in the integer unit.
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