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Interrupts5-8 SPRU733
If the interrupt service routine for an interrupt is too large to fit in a single fetch
packet, a branch to the location of additional interrupt service routine code is
required. Figure 5−3 shows that the interrupt service routine for INT4 was too
large for a single fetch packet, and a branch to memory location 1234h is
required to complete the interrupt service routine.
Note:
The instruction B LOOP branches into the middle of a fetch packet and
processes code starting at address 1234h. The CPU ignores code from
address 1220h−1230h, even if it is in parallel to code at address 1234h.
Figure 5−3. Interrupt Service Table With Branch to Additional Interrupt Service Code
Located Outside the IST
IST
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
Additional ISFP for INT4
1220h
The interrupt service routine
for INT4 includes this
7-instruction extension of
the interrupt ISFP.
Instr1
Instr2
B LOOP
Instr4
Instr5
Instr6
Instr7
Instr8
ISFP for INT4
080h
084h
088h
08Ch
090h
094h
098h
09Ch
Program memory
−
−
−
−
−
Instr9
Instr11
1224h
1228h
122Ch
1230h
LOOP: 1234h
1238h
123Ch
B IRP
000h
020h
040h
060h
080h
0A0h
0C0h
0E0h
100h
120h
140h
160h
180h
1A0h
1C0h
1E0h
Additional ISFP for INT4
1240h
Instr12
Instr13
Instr14
Instr15
−
−
−
1244h
1248h
124Ch
1250h
1254h
1258h
125Ch
−