Table 12. Interrupt Software Priority Levels; Figure 17. Interrupt Processing Flowchart; Figure 18. Priority Decision Process - STMicroelectronics ST72361 Auto Series Manual

ST72361xx-Auto
Table 12.
Level 0 (main)
Level 1
Level 2
Level 3 (= interrupt disable)

Figure 17. Interrupt processing flowchart

Servicing pending interrupts
As several interrupts can be pending at the same time, the interrupt to be taken into account
is determined by the following two-step process:
●
the highest software priority interrupt is serviced,
●
if several interrupts have the same software priority then the interrupt with the highest
hardware priority is serviced first.
Figure 18

Figure 18. Priority decision process

Interrupt software priority levels
Interrupt software priority
RESET
RESTORE PC, X, A, CC
FROM STACK
describes this decision process.
Same
HIGHEST HARDWARE
PRIORITY SERVICED
Doc ID 12468 Rev 3
Level
Low
High
PENDING
Y
INTERRUPT
Interrupt has the same or a
N
FETCH NEXT THE INTERRUPT
INSTRUCTION STAYS PENDING
Y
"IRET"
N
EXECUTE
INSTRUCTION
LOAD I1:0 FROM INTERRUPT SW REG.
LOAD PC FROM INTERRUPT VECTOR
PENDING
INTERRUPTS
Different
SOFTWARE
PRIORITY
HIGHEST SOFTWARE
PRIORITY SERVICED
I1
1
0
1
TLI
N
lower software priority
than current one
I1:0
STACK PC, X, A, CC
Interrupts
I0
0
1
0
1
Y
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