Nios II Classic Processor Reference Guide

ID 683620
Date 10/28/2016
Document Table of Contents Masking Interrupts with an External Interrupt Controller

Typical EIC implementations allow system software to mask individual interrupts. The method of masking individual interrupts is implementation-specific.

The status.IL field controls what level of external maskable interrupts can be serviced. The processor services a maskable interrupt only if its requested interrupt level is greater than status.IL.

An ISR can make run-time adjustments to interrupt nesting by manipulating status.IL. For example, if an ISR is running at level 5, to temporarily allow pre-emption by another level 5 interrupt, it can set status.IL to 4.

To enable all external interrupts, set status.IL to 0. To disable all external interrupts, set status.IL to 63.