AN 978: Nios® V Processor Migration Guidelines

ID 773196
Date 11/25/2024
Public
Document Table of Contents

6.7. Custom Instructions

Nios® V/g and Nios® II/f processors support custom instruction.
Table 32.  Custom Instructions Comparison
Feature Nios® V/g Processor Nios® II/f Processor
Supported custom instruction types
  • Multicycle
  • Extended
  • External Interface
  • Combinational
  • Multicycle
  • Extended
  • Internal Register Files
  • External Interface
Combinational instructions Implemented in two cycles. Implemented in a single cycle.
Multicycle instructions Supports variable length multicycle instructions. Supports fixed length and variable length multicycle instructions.
Extended instructions Apply the signal ctrl[31:0] to select the appropriate instruction. Apply the signal n[7:0] to select the appropriate instruction.
Internal Register Files instructions Not Supported Supported
Manager Interface Nios® V Processor Custom Instruction Manager Nios® II Processor Custom Instruction Manager
Agent Interface Nios® V Processor Custom Instruction Subordinate Nios® II Processor Custom Instruction Subordinate
Signals and Interface
  • clk
  • reset
  • data0
  • data1
  • enable
  • result
  • done
  • alu_result 5
  • ctrl
  • clk
  • reset
  • dataa
  • datab
  • start
  • result
  • done
  • clk_en 6
Built-in functions (To use non-integer types with instructions) Not supported Supported
FPH2 Hardware Replaced with internal FPU Supported
5 alu_result is not equivalent to clk_en.
6 Nios® V Processor Custom Instruction does not support clk_en signal.