Nios® V Processor Reference Manual

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ID 683632
Date 10/07/2024
Public
Document Table of Contents
Document Table of Contents x
1. Overview 2. Nios® V/c Processor 3. Nios® V/m Processor 4. Nios® V/g Processor 5. Nios V Processor Reference Manual Archives 6. Document Revision History for the Nios® V Processor Reference Manual
1. Overview x
1.1. Quartus® Prime Software Support
2. Nios® V/c Processor x
2.1. Processor Performance Benchmarks 2.2. Processor Pipeline 2.3. Processor Architecture 2.4. Programming Model 2.5. Core Implementation
2.3. Processor Architecture x
2.3.1. General-Purpose Register File 2.3.2. Arithmetic Logic Unit 2.3.3. Reset and Debug Signals 2.3.4. Memory and I/O Organization 2.3.5. Error Correction Code (ECC)
2.3.4. Memory and I/O Organization x
2.3.4.1. Instruction and Data Buses 2.3.4.2. Address Map
2.3.4.1. Instruction and Data Buses x
2.3.4.1.1. Instruction Manager Port 2.3.4.1.2. Data Manager Port 2.3.4.1.3. Choosing a Suitable Interface
2.4. Programming Model x
2.4.1. Privilege Levels
2.5. Core Implementation x
2.5.1. Instruction Set Reference
3. Nios® V/m Processor x
3.1. Processor Performance Benchmarks 3.2. Processor Pipeline 3.3. Processor Architecture 3.4. Programming Model 3.5. Core Implementation
3.1. Processor Performance Benchmarks x
3.1.1. Pipelined 3.1.2. Non-pipelined
3.2. Processor Pipeline x
3.2.1. Pipelined Architecture 3.2.2. Non-pipelined Architecture
3.3. Processor Architecture x
3.3.1. General-Purpose Register File 3.3.2. Arithmetic Logic Unit 3.3.3. Reset and Debug Signals 3.3.4. Control and Status Registers 3.3.5. Trap Controller 3.3.6. Memory and I/O Organization 3.3.7. RISC-V based Debug Module 3.3.8. Error Correction Code (ECC)
3.3.5. Trap Controller x
3.3.5.1. Exception Handling 3.3.5.2. Interrupt Handling
3.3.5.2. Interrupt Handling x
3.3.5.2.1. Timer and Software Interrupt Module
3.3.6. Memory and I/O Organization x
3.3.6.1. Instruction and Data Buses 3.3.6.2. Address Map
3.3.6.1. Instruction and Data Buses x
3.3.6.1.1. Instruction Manager Port 3.3.6.1.2. Data Manager Port 3.3.6.1.3. Choosing a Suitable Interface
3.3.7. RISC-V based Debug Module x
3.3.7.1. Debug Mode 3.3.7.2. Halt from Debug Module 3.3.7.3. Trigger 3.3.7.4. Abstract Commands in Debug Mode 3.3.7.5. Hardware/Software Interface
3.4. Programming Model x
3.4.1. Privilege Levels 3.4.2. Control and Status Registers (CSR) Mapping
3.4.1. Privilege Levels x
3.4.1.1. Machine Mode (M-mode) 3.4.1.2. Debug Mode (D-mode)
3.4.2. Control and Status Registers (CSR) Mapping x
3.4.2.1. Control and Status Register Field
3.5. Core Implementation x
3.5.1. Instruction Set Reference
4. Nios® V/g Processor x
4.1. Processor Performance Benchmarks 4.2. Processor Pipeline 4.3. Processor Architecture 4.4. Programming Model 4.5. Core Implementation
4.3. Processor Architecture x
4.3.1. General-Purpose Register File 4.3.2. Arithmetic Logic Unit 4.3.3. Multipy and Divide Units 4.3.4. Floating-Point Unit 4.3.5. Custom Instruction 4.3.6. Reset and Debug Signals 4.3.7. Control and Status Registers 4.3.8. Trap Controller 4.3.9. Memory and I/O Organization 4.3.10. RISC-V based Debug Module 4.3.11. Error Correction Code (ECC) 4.3.12. Branch Prediction 4.3.13. Lockstep Module
4.3.4. Floating-Point Unit x
4.3.4.1. IEEE 754 Exception Conditions 4.3.4.2. Floating Point Operations
4.3.4.2. Floating Point Operations x
4.3.4.2.1. Floating Point Classification
4.3.8. Trap Controller x
4.3.8.1. Exception Controller 4.3.8.2. Interrupt Controller
4.3.8.2. Interrupt Controller x
4.3.8.2.1. Timer and Software Interrupt Module
4.3.9. Memory and I/O Organization x
4.3.9.1. Instruction and Data Buses 4.3.9.2. Address Map 4.3.9.3. Cache Memory 4.3.9.4. Tightly Coupled Memory
4.3.9.1. Instruction and Data Buses x
4.3.9.1.1. Instruction Manager Port 4.3.9.1.2. Data Manager Port
4.3.9.3. Cache Memory x
4.3.9.3.1. Instruction Cache 4.3.9.3.2. Data Cache 4.3.9.3.3. Configurable Cache Memory 4.3.9.3.4. Bypassing Cache (Peripheral Region) 4.3.9.3.5. Using Cache Memory Effectively
4.3.9.4. Tightly Coupled Memory x
4.3.9.4.1. Instruction and Data Tightly Coupled Memory 4.3.9.4.2. Accessing Tightly Coupled Memory 4.3.9.4.3. Using Tightly Coupled Memory Effectively
4.3.10. RISC-V based Debug Module x
4.3.10.1. Debug Mode 4.3.10.2. Halt from Debug Module 4.3.10.3. Trigger 4.3.10.4. Abstract Commands in Debug Mode 4.3.10.5. Hardware/Software Interface
4.3.11. Error Correction Code (ECC) x
4.3.11.1. ECC Interface 4.3.11.2. ECC Error Injection 4.3.11.3. Affected CSR during ECC Event
4.4. Programming Model x
4.4.1. Privilege Levels 4.4.2. Control and Status Registers (CSR) Mapping
4.4.1. Privilege Levels x
4.4.1.1. Machine Mode (M-mode) 4.4.1.2. Debug Mode (D-mode)
4.4.2. Control and Status Registers (CSR) Mapping x
4.4.2.1. Control and Status Register Field
4.5. Core Implementation x
4.5.1. Instruction Set Reference
1. Overview
2. Nios® V/c Processor
3. Nios® V/m Processor
4. Nios® V/g Processor
5. Nios V Processor Reference Manual Archives
6. Document Revision History for the Nios® V Processor Reference Manual

4.2. Processor Pipeline

The Nios® V/g processor employs a five-stage pipeline.

Table 63.  Processor Pipeline Stages
Stage Denotation Function
F Instruction fetch
  • PC+4 calculation
  • Next instruction fetch
  • Pre-decode for register file read
D Instruction decode
  • Decode the instruction
  • Register file read data available
  • Hazard resolution and data forwarding
E Instruction execute
  • ALU operations
  • Memory address calculation
  • Branch resolution
  • CSR read/write
M Memory
  • Memory and multicycle operations
  • Register file write
  • Branch redirection
W Write back
  • Facilitates data dependency resolution by providing general-purpose register value.

The Nios® V/g processor implements the general-purpose register file using the M20K memory blocks. The processor takes one processing cycle to read from an M20K location. Therefore, the F-stage initiates register file reads so general-purpose register values are available in D-stage.

Writing to the M20K location takes two processing cycles. Therefore, the M-stage initiates writes to a general-purpose register. If there is a dependency to resolve, the M-stage carries forward the value to the W-stage.

The core resolves data dependencies in the D-stage. Operands can move from register file read or E-stage, M-stage, or W-stage.

Reasons for the pipeline stalling:
  • Data dependency—if the source operand is not available in D-stage, instruction in D-stage and F-stage stalls until the operand becomes available. The scenario can happen if destination general-purpose register of load or multicycle instruction in E-stage or M-stage is the source for instruction in D-stage.
  • Resource stall—if a memory operation or multicycle is pending in M-stage, the instructions in preceding stages stalls until M-stage completes the instruction.
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