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Operation, Priority determination – FUJITSU MB91460 SERIES FR60 User Manual

Page 334

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Chapter 24 Interrupt Control

5.Operation

5. Operation

The following section explains priority determination operation of interrupt control.

Priority determination

• The interrupt control circuit selects the highest priority factor from those that have been generated

simultaneously, and outputs the factor's interrupt level (ICR) and interrupt number (#) to the CPU.

• The priority level criteria of an interrupt cause are the following conditions.

• The value of the interrupt level is not 31. (31 is “interrupt disable”)

• The factors with the smallest interrupt level.

• Among these, the factor that has the smallest interrupt number.

• If nothing is applicable by the above-mentioned criteria, interrupt level 31 (11111

B

) is sent to the CPU. In this

case, the interrupt number is indeterminate.

CPU processing

Interrupt cause generated

The interrupt request flag is set to “1”.

The interrupt request is transmitted to

the interrupt control circuit.

Are interrupt requests enabled?

The interrupt level and the interrupt number

are transmitted to the CPU.

Is not the corresponding interrupt disabled?

(ICR) < 31?

Which interrupt has the lowest level

among the interrupt requests?

Which interrupt has the lowest

number (#) among the lowest

interrupt requests?

Interrupt control circuit

Interrupt level = 31
Interrupt number
= indeterminate

Wait until the executed instructions finish

Is the interrupt level higher than

the interrupt mask level?

(ICR) < (ILM)

Transition processing to interrupts

- Save to the system stack (PS and PC)
- Set an interrupt level to ILM
- System stack enabled
- Branch to the interrupt routine

(PC <= interrupt vector)

The Flow of the Interrupt Process

Are interrupts enabled?

I flag = 1

YES

YES

The lowest interrupts

The interrupt with
the lowest number

YES

YES

NO

NO

NO

Priority determination