Nios II Custom Instruction User Guide

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ID 683242
Date 4/27/2020
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 Intel® 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

6.4. Floating Point Hardware 2 Operations

The table below provides a detailed summary of the FPH2 operations. The values “a” and “b” are assumed to be single-precision floating point values. The following list provides detailed information about each column:
  • Operation 8—Provides the name of the floating point operation. The names match the names of the corresponding GCC floating point command-line options except for “round”, which has no GCC support.
  • N—Provides the 8-bit fixed custom instruction N value for the operation. FPH2 component uses fixed N values that occupy the top 32 Nios II custom instruction N values (224 to 255). The FPH1 also use fixed N values (252 to 255) and the FPH2 assign the same operations to those N values to maintain compatibility.
  • Cycle 9—Specifies the number of cycles it takes to execute the instruction. A combinatorial custom instruction takes 1 cycle. A multi-cycle custom instruction always requires at least 2 cycles. An N-cycle custom instruction has N-2 register stages inside the custom instruction because the Nios II registers the result from the custom instruction and also allows another cycle for g wire delays in the source operand bypass multiplexers. The Cycle column does not include the extra cycles (maximum of 2) required because the Nios II/f processor stalls the instruction following the multi-cycle custom instruction if that instruction uses the result within 2 cycles. These extra cycles are required because multi-cycle instructions are late-result instructions.
  • Result—Describes the computation performed by the operation.
  • Subnormal—Describes how the operation treats subnormal inputs and subnormal outputs.
  • Rounding 10—Describes how the FPH2 component rounds the result. The possible choices are Nearest, Truncation, Faithful, and none.
  • GCC Inference—Shows the C code from which GCC infers the custom instruction operation.
Table 15.  FPH2 Operation Summary
Operation N Cycles Result Subnormal Rounding GCC Inference
fdivs 255 16 a/b flush-to-0 Nearest a/b
fsubs 254 5 a-b flush-to-0 Faithful a-b
fadds 253 5 a+b flush-to-0 Faithful a+b
fmuls 252 4 a*b flush-to-0 Faithful a*b
fsqrts 251 8 sqrt(a) flush-to-0 Faithful sqrtf()
floatis 250 4 int_to_float(a) Does not apply Does not apply Casting
fixsi 249 2 float_to_int(a) flush-to-0 Truncation Casting
round 248 2 float_to_int(a) flush-to-0 Nearest lroundf()11
reserved 234 to 247 Undefined undefined      
fmins 233 1 (a<b) ? a : b supported None fminf()11
fmaxs 232 1 (a<b) ? b : a supported None fmaxf()11
fcmplts 231 1 (a<b) ? 1 : 0 supported None a<b
fcmples 230 1 (a≤b) ? 1 : 0 supported None a<=b
fcmpgts 229 1 (a>b) ? 1 : 0 supported None a>b
fcmpges 228 1 (a≥b) ? 1 : 0 supported None a>=b
fcmpeqs 227 1 (a=b) ? 1 : 0 supported None a==b
fcmpnes 226 1 (a≠b) ? 1 : 0 supported None a!=b
fnegs 225 1 -a supported None -a
fabss 224 1 |a| supported None fabsf()
Related Information
8 For more information, refer to "-mcustom-<operation>".
9 For more information, refer to the Nios II Processor Reference Guide.
10 For more information, refer to "Rounding Schemes". A rounding of “none” means that the result does not need to be rounded.
11 Nios II GCC cannot reliably replace calls to these newlib floating point functions with the equivalent custom instruction. For information about using these functions, refer to "C Macros for round(), fmins(), and fmaxs()".
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