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2-20
CPU
(Example of pre-processing by the interrupt handler)
1. The registers are saved.
The saved registers are those used by the interrupt handler.
2. The interrupt group analysis is executed.
2.1 The interrupt acknowledge sequence is executed.
Interrupt acknowledge consists of reading out the interrupt accept group register (IAGR) to obtain the group
number of the interrupt group with the highest priority among the specified interrupt levels.
2.2 The leading address of the interrupt handler for each level is generated.
2.3 Control is transferred to the interrupt handler for each level.
3. When there are multiple factors within the same group, the interrupt control register (GnICR) is read out to
designate the factor.
* In case of non-maskable interrupts, the factor is specified by accessing the NMICR directly without accessing
the IAGR.
4. Control is transferred to the interrupt handler for each factor.
Note that because this microcontroller uses a store buffer when writing data via the bus controller, it is necessary,
when releasing the interrupt factor, to read the appropriate register immediately after clearing the interrupt
factor in order to wait for the factor in the GnICR to be cleared completely.
(Example of post-processing by the interrupt handler)
5. The registers are restored.
The restored registers are those saved by the pre-processing.
6. The RTI instruction is executed and control returns to the program before the interrupt.
Fig. 2-5-5 shows the interrupt sequence flow. (when not accepting nested interrupts)
The numbers in the figure correspond to the numbers of processing performed by the interrupt handler in the
previous section.
Fig. 2-5-5 Interrupt Sequence Flow
Interrupt processing
and interrupt request
cancel
Program Handler (pre-processing)
Interrupt
max. 11 Cycles
Interrupt processing by hardware
RTI
Interrupt
handler
Handler (post-processing)
1
2
3
4
5
6
Processing for each level
Processing for each group
Processing for
each factor
3 Cycles