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5-7InterruptsSPRU733
5.1.2.1 Interrupt Service Fetch Packet (ISFP)
An ISFP is a fetch packet used to service an interrupt. Figure 5−2 shows an
ISFP that contains an interrupt service routine small enough to fit in a single
fetch packet (FP). To branch back to the main program, the FP contains a
branch to the interrupt return pointer instruction (B IRP). This is followed by a
NOP 5 instruction to allow the branch target to reach the execution stage of
the pipeline.
Note:
If the NOP 5 was not in the routine, the CPU would execute the next five
execute packets that are associated with the next ISFP.
Figure 5−2. Interrupt Service Fetch Packet
Instr3
Interrupt service table
(IST)
Instr2
Instr4
Instr5
Instr6
B IRP
NOP 5
ISFP for INT6
000h
020h
040h
060h
080h
0A0h
0C0h
0E0h
100h
120h
140h
160h
180h
1A0h
1C0h
1E0h
0C0h
0C4h
0C8h
0CCh
0D0h
0D4h
0D8h
0DCh
The interrupt service
routine for INT6 is short
enough to be contained
in a single fetch packet.
Program memory
RESET
ISFP
NMI ISFP
Reserved
Reserved
INT4 ISFP
INT5 ISFP
INT6 ISFP
INT7 ISFP
INT8 ISFP
INT9 ISFP
INT10 ISFP
INT11 ISFP
INT12 ISFP
INT13 ISFP
INT14 ISFP
INT15 ISFP
Instr1