Multiple Interrupt Servicing Control - NEC PD703114 User Manual

7.6 Multiple Interrupt Servicing Control

Multiple interrupt servicing control is a process by which an interrupt request that is currently being processed can
be interrupted during processing if there is an interrupt request with a higher priority level, and the higher priority
interrupt request is received and processed first.
If there is an interrupt request with a lower priority level than the interrupt request currently being processed, that
interrupt request is held pending.
Maskable interrupt multiple processing control is executed when interrupts are enabled (ID = 0). Thus, if multiple
interrupts are executed, it is necessary for interrupts to be enabled (ID = 0) even during an interrupt servicing routine.
If a maskable interrupt or a software exception is generated in a maskable interrupt or software exception service
program, it is necessary to save EIPC and EIPSW.
This is accomplished by the following procedure.
(1) Acknowledgment of maskable interrupts in service program
Service program of maskable interrupt or exception
...
...
• EIPC saved to memory or register
• EIPSW saved to memory or register
• EI instruction (interrupt acknowledgment enabled)
...
...
...
...
• DI instruction (interrupt acknowledgment disabled)
• Saved value restored to EIPSW
• Saved value restored to EIPC
• RETI instruction
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CHAPTER 7 INTERRUPT/EXCEPTION PROCESSING FUNCTION
User's Manual U15195EJ5V0UD
← Maskable interrupt acknowledgment