Nios® V Processor Reference Manual

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ID 683632
Date 5/26/2023
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Document Table of Contents
Document Table of Contents x
1. Overview 2. Nios® V/m Processor 3. Nios® V/g Processor 4. Nios V Processor Reference Manual Archives 5. Document Revision History for the Nios® V Processor Reference Manual
1. Overview x
1.1. Intel® Quartus® Prime Software Support
2. Nios® V/m 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. Control and Status Registers 2.3.5. Exception Controller 2.3.6. Interrupt Controller 2.3.7. Memory and I/O Organization 2.3.8. RISC-V based Debug Module
2.3.6. Interrupt Controller x
2.3.6.1. Timer and Software Interrupt Module
2.3.7. Memory and I/O Organization x
2.3.7.1. Instruction and Data Buses 2.3.7.2. Address Map
2.3.7.1. Instruction and Data Buses x
2.3.7.1.1. Instruction Manager Port 2.3.7.1.2. Data Manager Port
2.3.8. RISC-V based Debug Module x
2.3.8.1. Debug Mode 2.3.8.2. Halt from Debug Module 2.3.8.3. Trigger 2.3.8.4. Abstract Commands in Debug Mode 2.3.8.5. Hardware/Software Interface
2.4. Programming Model x
2.4.1. Privilege Levels 2.4.2. Control and Status Registers (CSR) Mapping
2.4.1. Privilege Levels x
2.4.1.1. Machine Mode (M-mode) 2.4.1.2. Debug Mode (D-mode)
2.4.2. Control and Status Registers (CSR) Mapping x
2.4.2.1. Control and Status Register Field
2.5. Core Implementation x
2.5.1. Instruction Set Reference
3. Nios® V/g Processor x
3.1. Processor Performance Benchmarks 3.2. Processor Pipeline 3.3. Processor Architecture 3.4. Programming Model 3.5. Core Implementation
3.3. Processor Architecture x
3.3.1. General-Purpose Register File 3.3.2. Arithmetic Logic Unit 3.3.3. Multipy and Divide Units 3.3.4. Custom Instruction 3.3.5. Reset and Debug Signals 3.3.6. Control and Status Registers 3.3.7. Exception Controller 3.3.8. Interrupt Controller 3.3.9. Memory and I/O Organization 3.3.10. RISC-V based Debug Module
3.3.8. Interrupt Controller x
3.3.8.1. Timer and Software Interrupt Module
3.3.9. Memory and I/O Organization x
3.3.9.1. Instruction and Data Buses 3.3.9.2. Address Map 3.3.9.3. Cache Memory
3.3.9.1. Instruction and Data Buses x
3.3.9.1.1. Instruction Manager Port 3.3.9.1.2. Data Manager Port
3.3.9.3. Cache Memory x
3.3.9.3.1. Instruction Cache 3.3.9.3.2. Data Cache 3.3.9.3.3. Configurable Cache Memory 3.3.9.3.4. Bypassing Cache (Peripheral Region) 3.3.9.3.5. Using Cache Memory Effectively
3.3.10. RISC-V based Debug Module x
3.3.10.1. Debug Mode 3.3.10.2. Halt from Debug Module 3.3.10.3. Trigger 3.3.10.4. Abstract Commands in Debug Mode 3.3.10.5. 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
1. Overview
2. Nios® V/m Processor
3. Nios® V/g Processor
4. Nios V Processor Reference Manual Archives
5. Document Revision History for the Nios® V Processor Reference Manual

3.3.10.1. Debug Mode

You can enter the Debug Mode, as specified in the RISC-V architecture specification, in the following ways:

  1. Halt from Debug Module
  2. Software breakpoints
  3. Trigger
Upon entering Debug Mode, Nios® V processor completes the instruction in W-stage. By the order of priority, instruction in M-stage, E-stage, D-stage or F-stage takes the interrupt.

  • When there is a valid instruction, Program Counter writes to the Debug Program Counter, .dpc.

  • If the instruction in M-stage is not valid, then instruction in E-stage takes the interrupt and so on and so forth.

  • If there is no valid instruction in the pipeline, the Program Counter for the next instruction writes to the Debug Program Counter, .dpc.

Note: For branches, the next Program Counter depends on whether a branch was taken or not taken, and whether the branch prediction (if any) was correct.
Debug Module selects Hardware Thread (Hart); which can be in one of the following states:
  1. Non-existent: Debug Module probes a hart which does not exist.
  2. Unavailable: Reset or temporary shutdown.
  3. Running: Normal operation outside of debug.
  4. Halted: Hart is said to be halted when it is in debug mode.
Figure 8. Debug Module Block Diagram
Level Two Title