Nios® II Processor Reference Guide

ID 683836
Date 10/22/2020
Public
Document Table of Contents

1.4.2.3. Custom Instructions

Like custom peripherals, custom instructions allow you to increase system performance by augmenting the processor with custom hardware. You can achieve significant performance improvements, often on the order of 10 to 100 times, by implementing performance-critical operations in hardware using custom instruction logic.

The custom logic is integrated into the Nios® II processor’s arithmetic logic unit (ALU). Similar to native Nios II instructions, custom instruction logic can take values from up to two source registers and optionally write back a result to a destination register.

Because the processor is implemented on reprogrammable Intel FPGAs, software and hardware engineers can work together to iteratively optimize the hardware and test the results of software running on hardware.

From the software perspective, custom instructions appear as machine-generated assembly macros or C functions, so programmers do not need to understand assembly language to use custom instructions.

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