Nios II Classic Software Developer’s Handbook

ID 683282
Date 5/14/2015
Public
Document Table of Contents

8.3.1.8.2. Nested Hardware Interrupts with an External Interrupt Controller

The HAL enhanced interrupt API supports nested hardware interrupts, also known as interrupt pre-emption. A device driver must be specifically written to function correctly under pre-emption.

Legacy device drivers do not publish the isr_preemption_supported property. Therefore the SBT assumes that they do not support pre-emption. If your legacy custom driver supports pre-emption, and you want to allow pre-emption in the BSP, you must update the driver to use the enhanced HAL interrupt API.

The HAL enhanced interrupt API also supports automatic pre-emption. Automatic pre-emption means that maskable exceptions remain enabled when the processor accepts the hardware interrupt.

For more information about pre-emption with an EIC, refer to the “Managing Pre-Emption” chapter.

In the vector table, the HAL inserts a branch to the correct funnel for each hardware interrupt, depending on the pre-emption settings.