Nios II Custom Instruction User Guide

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ID 683242
Date 4/14/2025
Public
Document Table of Contents
Document Table of Contents x
1. Nios II Custom Instruction Overview 2. Custom Instruction Hardware Interface 3. Custom Instruction Software Interface 4. Design Example: Cyclic Redundancy Check 5. Introduction to Nios® II Floating Point Custom Instructions 6. Nios II Floating Point Hardware 2 Component 7. Nios® II Floating Point Hardware (FPH1) Component 8. Document Revision History for Nios II Custom Instruction User Guide
1. Nios II Custom Instruction Overview x
1.1. Custom Instruction Implementation
1.1. Custom Instruction Implementation x
1.1.1. Custom Instruction Hardware Implementation 1.1.2. Custom Instruction Software Implementation
2. Custom Instruction Hardware Interface x
2.1. Custom Instruction Types
2.1. Custom Instruction Types x
2.1.1. Combinational Custom Instructions 2.1.2. Multicycle Custom Instructions 2.1.3. Extended Custom Instructions 2.1.4. Internal Register File Custom Instructions 2.1.5. External Interface Custom Instructions
2.1.1. Combinational Custom Instructions x
2.1.1.1. Combinational Custom Instruction Ports 2.1.1.2. Combinational Custom Instruction Timing
2.1.2. Multicycle Custom Instructions x
2.1.2.1. Multicycle Custom Instruction Ports 2.1.2.2. Multicycle Custom Instruction Timing
2.1.3. Extended Custom Instructions x
2.1.3.1. Extended Custom Instruction Timing
2.1.4. Internal Register File Custom Instructions x
2.1.4.1. Internal Register File Custom Instruction Example 2.1.4.2. Internal Register File Custom Instruction Ports
3. Custom Instruction Software Interface x
3.1. Custom Instruction Software Examples 3.2. Built-in Functions and User-defined Macros 3.3. Custom Instruction Assembly Language Interface
3.2. Built-in Functions and User-defined Macros x
3.2.1. Built-in Functions with No Return Value 3.2.2. Built-in Functions that Return a Value of Type Int 3.2.3. Built-in Functions that Return a Value of Type Float 3.2.4. Built-in Functions that Return a Pointer Value
3.3. Custom Instruction Assembly Language Interface x
3.3.1. Custom Instruction Assembly Language Syntax 3.3.2. Custom Instruction Assembly Language Examples 3.3.3. Custom Instruction Word Format
3.3.3. Custom Instruction Word Format x
3.3.3.1. Select Index Field (N)
4. Design Example: Cyclic Redundancy Check x
4.1. Building the CRC Example Hardware 4.2. Building the CRC Example Software
4.1. Building the CRC Example Hardware x
4.1.1. Setting up the Environment for the CRC Example Design 4.1.2. Opening the Component Editor 4.1.3. Specifying the Custom Instruction Component Type 4.1.4. Displaying the Custom Instruction Block Symbol 4.1.5. Adding the CRC Custom Instruction HDL Files 4.1.6. Configuring the Custom Instruction Parameter Type 4.1.7. Setting Up the CRC Custom Instruction Interfaces 4.1.8. Configuring the Custom Instruction Signal Type 4.1.9. Saving and Adding the CRC Custom Instruction 4.1.10. Generating and Compiling the CRC Example System
4.1.7. Setting Up the CRC Custom Instruction Interfaces x
4.1.7.1. Specifying Additional Interfaces
4.2. Building the CRC Example Software x
4.2.1. Running and Analyzing the CRC Example Software 4.2.2. Using the User-defined Custom Instruction Macro
4.2.1. Running and Analyzing the CRC Example Software x
4.2.1.1. Output of the CRC Design Example Software Run on a Cyclone V E FPGA Development Kit using the Quartus® Prime Software v15.1.
5. Introduction to Nios® II Floating Point Custom Instructions x
5.1. Floating Point Background 5.2. IEEE 754 Format 5.3. Rounding Schemes 5.4. Special Floating Point Cases
5.2. IEEE 754 Format x
5.2.1. Unit in the Last Place 5.2.2. Floating Point Value Encoding
5.3. Rounding Schemes x
5.3.1. Nearest Rounding 5.3.2. Truncation Rounding 5.3.3. Faithful Rounding 5.3.4. Rounding Examples
6. Nios II Floating Point Hardware 2 Component x
6.1. Overview of the Floating Point Hardware 2 Component 6.2. Floating Point Hardware 2 IEEE 754 Compliance 6.3. IEEE 754 Exception Conditions with FPH2 6.4. Floating Point Hardware 2 Operations 6.5. Building the FPH2 Example Hardware 6.6. Building the FPH2 Example Software 6.7. FPH2 Implementation of GCC Options 6.8. Nios II FPH2 and the Newlib Library 6.9. C Macros for round(), fmins(), and fmaxs()
6.6. Building the FPH2 Example Software x
6.6.1. FPH2 and Nios II GCC 6.6.2. Floating Point Hardware 2 Conversions 6.6.3. Nios II FPH2 Software Options
6.6.3. Nios II FPH2 Software Options x
6.6.3.1. -mcustom-<operation> 6.6.3.2. Nios II FPH2 Pragmas 6.6.3.3. -mcustom-fpu-cfg
6.7. FPH2 Implementation of GCC Options x
6.7.1. -fno-math-errno 6.7.2. -fsingle-precision-constant 6.7.3. -funsafe-math-optimizations 6.7.4. -ffinite-math-only 6.7.5. -fno-trapping-math 6.7.6. -frounding-math
7. Nios® II Floating Point Hardware (FPH1) Component x
7.1. Creating the FPH1 Example Hardware 7.2. Adding FPH1 to the Design and Configuring the Device 7.3. Building the FPH1 Example Software 7.4. Nios II FPH1 and the Newlib Library 7.5. Assessing Your Floating Point Optimization Needs 7.6. Hardware Divide Considerations with FPH1
7.3. Building the FPH1 Example Software x
7.3.1. Creating the FPH1 Software Project 7.3.2. Running and Analyzing the FPH1 Example Software 7.3.3. Software Implementation for FPH1
1. Nios II Custom Instruction Overview
2. Custom Instruction Hardware Interface
3. Custom Instruction Software Interface
4. Design Example: Cyclic Redundancy Check
5. Introduction to Nios® II Floating Point Custom Instructions
6. Nios II Floating Point Hardware 2 Component
7. Nios® II Floating Point Hardware (FPH1) Component
8. Document Revision History for Nios II Custom Instruction User Guide

5.2.2. Floating Point Value Encoding

The table below shows how single-precision values are encoded across the 32-bit range from 0x0000_0000 to 0xffff_ffff. Single-precision floating point numbers have the following characteristics:

  • Precision (ρ) = 24 bits (23 bits in FRAC plus one hidden bit)
  • Radix (β) = 2
  • emin = -126
  • emax = 127

The most-significant bit of FRAC is 0 for signaling NaNs (sNaN) and 1 for quiet NaNs (qNaN).

Table 10.  Encoding of Values
Hexadecimal Value Name S EXP FRAC Value (Decimal)
0x0000_0000 +0 0 0x00 0x00_0000 0.0
0x0000_0001 min pos subnormal 0 0x00 0x00_0001 1.40129846e–45 (βemin-ρ+1 = 2-126-24+1 = 2-149)
0x007f_ffff max pos subnormal 0 0x00 0x7f_ffff 1.1754942e-38
0x0080_0000 min pos normal 0 0x01 0x00_0000 1.17549435e–38 (βemin = 2-126)
0x3f80_0000 1 0 0x7f 0x00_0000 1.0 (1.0x20)
0x4000_0000 2 0 0x80 0x00_0000 2.0 (1.0x21)
0x7f7f_ffff max pos normal 0 0xfe 0x7f_ffff 3.40282347e+38 ((β – β1- ρ) * 2emax = (2 – 21-24) * 2127 = (2 – 223) * 2127
0x7f80_0000 +∞ 0 0xff 0x00_0000  
0x7f80_0001 min sNaN (pos sign) 0 0xff 0x00_0001  
0x7fdf_ffff max sNaN (pos sign) 0 0xff 0x3f_ffff  
0x7fe0_0000 min qNaN (pos sign) 0 0xff 0x40_0000  
0x7fff_ffff max qNaN (pos sign) 0 0xff 0x7f_ffff  
0x8000_0000 -0 1 0x00 0x00_0000 -0.0
0x8000_0001 max neg subnormal 1 0x00 0x00_0001 -1.40129846e–45
0x807f_ffff min neg subnormal 1 0x00 0x7f_ffff -1.1754942e-38
0x8080_0000 max neg normal 1 0x01 0x00_0000 -1.17549435e–38
0xff7f_ffff min neg normal 1 0xfe 0x7f_ffff -3.40282347e+38
0xff80_0000 -∞ 1 0xff 0x00_0000  
0xff80_0001 max sNaN (neg sign) 1 0xff 0x00_0001  
0xffdf_ffff min sNaN (neg sign) 1 0xff 0x3f_ffff  
0xffe0_0000 max qNaN (neg sign) 1 0xff 0x40_0000  
0xffff_ffff min qNaN (neg sign) 1 0xff 0x7f_ffff  
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