Nios II Custom Instruction User Guide

ID 683242
Date 4/27/2020
Document Table of Contents
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1.1. Custom Instruction Implementation

Nios II custom instructions are custom logic blocks adjacent to the arithmetic logic unit (ALU) in the processor’s datapath.

When custom instructions are implemented in a Nios II system, each custom operation is assigned a unique selector index. The selector index allows software to specify the desired operation from among up to 256 custom operations. The selector index is determined at the time the hardware is instantiated with the Platform Designer or Platform Designer (Standard) software. Platform Designer exports the selection index value to system.h for use by the Nios II software build tools.