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Architecture
60
After an exception handler has executed to perform exception processing, it must issue an RFE
(Restore From Exception) instruction to restore the system to its previous status.
The RFE instruction returns control to processing that was in progress when the exception occurred.
When a RFE instruction is executed, the previous interrupt enabled bit (IEp) and previous operating
mode bit (KUp) in the Status register are copied to the corresponding current bits (IEc and KUc).
The old mode bits (IEo and KUo) are copied to the corresponding previous mode bits (IEp and KUp).
The old mode bits (IEo and KUo) retain their current values.
Likewise, the previous data cache auto-lock mode bit (DALp) and previous instruction cache auto-
lock mode bit (IALp) in the Cache register are copied to the corresponding current bits (DALc and
IALc). The old mode bits (DALo and IALo) are copied to the corresponding previous mode bits
(DALp and IALp). The old mode bits (DALo and IALo) retain their current values.
Figure 6-7 shows how the RFE instruction works.
KUo IEo KUp IEp KUc IEc
RFE instruction issued
KUo IEo KUp IEp KUc IEc
(a) Status register
0 0 0 IAL
o
DAL
o
IAL
p
DAL
p
IAL
c
DAL
c
0 0 0 0 0 0 0 0
RFE instruction issued
0 0 IAL
o
DAL
o
IAL
p
DAL
p
IAL
c
DAL
c
0 0 0 0 0 0 0 0
(b) Cache register
Figure 6-7. Status register and cache register when an RFE instruction is issued