Exceptions
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
6-7
Register settings for the external interrupt exception are shown in
Table 6-6
.
6.1.2.6
Alignment Exception (0x00600)
This section describes conditions that can cause alignment exceptions in the processor. Similar to DSI
exceptions, alignment exceptions use SRR0 and SRR1 to save the machine state and DSISR to determine
the source of the exception. An alignment exception occurs when no higher priority exception exists and
the implementation cannot perform a memory access for one of the following reasons:
•
The operand of lmw, stmw, lwarx, or stwcx. is not aligned.
•
The instruction is lmw, stmw, lswi, lswx, stswi, or stswx and the processor is in little-endian mode.
•
An unaligned load or store in little-endian mode.
For lmw, stmw, lswi, lswx, stswi, and stswx instructions in little-endian mode, an alignment exception
always occurs. For lmw and stmw instructions with an operand that is not aligned in big-endian mode, and
for lwarx and stwcx. with an operand that is not aligned in either endian mode, an implementation may
yield boundedly-undefined results instead of causing an alignment exception. For all other cases listed
above, an implementation may execute the instruction correctly instead of causing an alignment exception.
The register settings for alignment exceptions are shown in
Table 6-7
.
Table 6-6. Register Settings after an External Interrupt
Register
Setting Description
SRR0
Set to the effective address of the instruction that the processor would have attempted to execute next if
no interrupt conditions were present.
SRR1
0
Loaded with equivalent bits from the MSR
1–4
Cleared
5–9
Loaded with equivalent bits from the MSR
10–15
Cleared
16–31
Loaded with equivalent bits from the MSR
Note that depending on the implementation, reserved bits in the MSR may not be copied to SRR1.
MSR
POW 0
ILE
—
EE
0
PR
0
FP
0
ME —
SE
0
BE
0
IP
—
IR
0
DR
0
RI
0
LE
Set to value of ILE
Table 6-7. Register Settings after an Alignment Exception
Register
Setting Description
SRR0
Set to the effective address of the instruction that caused the exception.
SRR1
0
Loaded with equivalent bits from the MSR
1–4
Cleared
5–9
Loaded with equivalent bits from the MSR
10–15
Cleared
16–31
Loaded with equivalent bits from the MSR
Note that depending on the implementation, reserved bits in the MSR may not be copied to SRR1.
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