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January 2011 Altera Corporation Nios II Custom Instruction User Guide

1. Nios II Custom Instruction Overview

When you design a system that includes an Altera Nios II embedded processor, you

can accelerate time-critical software algorithms by adding custom instructions to the

Nios II processor instruction set. Custom instructions allow you to reduce a complex

sequence of standard instructions to a single instruction implemented in hardware.

You can use this feature for a variety of applications, for example, to optimize

software inner loops for digital signal processing (DSP), packet header processing,

and computation-intensive applications. In SOPC Builder, the Nios II parameter

editor provides a GUI to add custom instructions to the Nios II processor. In Qsys,

each custom instruction is a separate component in the Qsys system. You can add as

many as 256 custom instructions to your system.

In SOPC Builder, the custom instruction logic connects directly to the Nios II

arithmetic logic unit (ALU) as shown in Figure 1–1.

This chapter contains the following sections:

■ “Custom Instruction Overview”

■ “Custom Instruction Types” on page 1–3

For information about the custom instruction software interface, refer to Chapter 2,

Software Interface. For step-by-step instructions for implementing a custom

instruction, refer to Chapter 3, Implementing a Nios II Custom Instruction in SOPC

Builder or Chapter 4, Implementing a Nios II Custom Instruction in Qsys.

Figure 1–1. Custom Instruction Logic Connects to the Nios II ALU in SOPC Builder Systems

Nios II Embedded Processor

Result

Nios II

ALU

Custom

Logic

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