CHAPTER 7 INTERRUPTION/EXCEPTION PROCESSING FUNCTION
277
User’s Manual U14359EJ4V0UM
Figure 7-6. Example of Processing in Which Another Interrupt Request Is Issued While an
Interrupt Is Being Serviced (2/2)
Main routine
EI
Interrupt request i
(level 2)
Servicing of i
Servicing of k
Interrupt
request j
(level 3)
Servicing of j
Interrupt request l
(level 2)
EI
EI
EI
Interrupt request o
(level 3)
Interrupt request s
(level 1)
Interrupt request k
(level 1)
Servicing of l
Servicing of n
Servicing of m
Servicing of s
Servicing of u
Servicing of t
Interrupt
request m
(level 3)
Interrupt request n
(level 1)
Servicing of o
Interrupt
request p
(level 2)
Interrupt
request q
(level 1)
Interrupt
request r
(level 0)
Interrupt request u
(level 2)
Note 2
Interrupt
request t
(level 2)
Note 1
Servicing of p
Servicing of q
Servicing of r
EI
If levels 3 to 0 are acknowledged
Interrupt request j is held pending because its
priority is lower than that of i.
k that occurs after j is acknowledged because it
has the higher priority.
Interrupt requests m and n are held pending
because servicing of l is performed in the interrupt
disabled status.
Pending interrupt requests are acknowledged after
servicing of interrupt request l.
At this time, interrupt request n is acknowledged
first even though m has occurred first because the
priority of n is higher than that of m.
Pending interrupt requests t and u are
acknowledged after servicing of s.
Because the priorities of t and u are the same, u is
acknowledged first because it has the higher
default priority, regardless of the order in which the
interrupt requests have been generated.
Caution
To perform multiple interrupt servicing, the values of the EIPC and EIPSW registers must be
saved before executing the EI instruction. When returning from multiple interrupt servicing,
restore the values of EIPC and EIPSW after executing the DI instruction.
Notes 1.
Lower default priority
2.
Higher default priority
