Nios® V Processor Software Developer Handbook

ID 743810
Date 4/07/2025
Public
Document Table of Contents

9.2. Hardware Interrupt Controllers

Altera implements Nios® V processor trap handling based on the RISC-V specification. The configuration of Nios® V trap processing logic depends on either the Core-Local Interruptor (CLINT) or the Core-Local Interrupt Controller (CLIC). When you instantiate the Nios® V processor in the system integration tool Platform Designer, you can configure the trap processing logic (Interrupt Mode) as either Direct Mode, Vectored Mode or CLIC mode.

Once the processor exits reset, its Machine Trap-Vector Base Address (mtvec) register always starts with the CLINT-Direct mode encoding. During processor runtime, you must reconfigure the interrupt controller based on the selected Interrupt Mode in Platform Designer. This is done by writing the mtvec register with the appropriate Interrupt Mode encoding.
Note: This mtvec reconfiguration is included in the Altera HAL firmware.