Nios® V Processor Reference Manual

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Date 5/25/2025
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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 Architecture 2.3. Programming Model 2.4. Core Implementation
2.2. Processor Architecture x
2.2.1. General-Purpose Register File 2.2.2. Arithmetic Logic Unit 2.2.3. Reset Signals 2.2.4. Memory and I/O Organization 2.2.5. Error Correction Code (ECC)
2.2.4. Memory and I/O Organization x
2.2.4.1. Instruction and Data Buses 2.2.4.2. Address Map
2.2.4.1. Instruction and Data Buses x
2.2.4.1.1. Instruction Manager Port 2.2.4.1.2. Data Manager Port 2.2.4.1.3. Choosing a Suitable Interface
2.3. Programming Model x
2.3.1. Privilege Levels
2.4. Core Implementation x
2.4.1. 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. Instruction Cycles 3.3.6. Trap Controller (CLINT) 3.3.7. Memory and I/O Organization 3.3.8. RISC-V based Debug Module 3.3.9. Error Correction Code (ECC)
3.3.6. Trap Controller (CLINT) x
3.3.6.1. Related Control and Status Register 3.3.6.2. Direct Mode 3.3.6.3. Vectored Mode
3.3.6.1. Related Control and Status Register x
3.3.6.1.1. Machine Status Register (mstatus) 3.3.6.1.2. Machine Trap-Vector Base-Address Register (mtvec) 3.3.6.1.3. Machine Interrupt Register (mip and mie) 3.3.6.1.4. Machine Exception Program Counter Register (mepc) 3.3.6.1.5. Machine Cause Register (mcause) 3.3.6.1.6. Machine Trap Value Register (mtval)
3.3.6.2. Direct Mode x
3.3.6.2.1. Hardware Implementation 3.3.6.2.2. Software Implementation
3.3.6.3. Vectored Mode x
3.3.6.3.1. Hardware Implementation 3.3.6.3.2. Software Implementation
3.3.7. Memory and I/O Organization x
3.3.7.1. Instruction and Data Buses 3.3.7.2. Address Map
3.3.7.1. Instruction and Data Buses x
3.3.7.1.1. Instruction Manager Port 3.3.7.1.2. Data Manager Port 3.3.7.1.3. Choosing a Suitable Interface
3.3.8. RISC-V based Debug Module x
3.3.8.1. Debug Module 3.3.8.2. Abstract Commands 3.3.8.3. Program Buffer 3.3.8.4. Debug Mode 3.3.8.5. Hardware Trigger Module 3.3.8.6. JTAG Debug Transport Module 3.3.8.7. Nios® V Processor Implementation
3.3.8.1. Debug Module x
3.3.8.1.1. Reset/Halt/Run Control 3.3.8.1.2. Hart States 3.3.8.1.3. Debug Module Register
3.3.8.2. Abstract Commands x
3.3.8.2.1. Access Register Command 3.3.8.2.2. Using Access Register Command
3.3.8.3. Program Buffer x
3.3.8.3.1. Using Program Buffer
3.3.8.4. Debug Mode x
3.3.8.4.1. Enter Debug Mode 3.3.8.4.2. Exit Debug Mode 3.3.8.4.3. Core Debug Registers
3.3.8.5. Hardware Trigger Module x
3.3.8.5.1. Trigger Registers 3.3.8.5.2. Type of Address/Data Match Triggers 3.3.8.5.3. Using Triggers
3.3.8.6. JTAG Debug Transport Module x
3.3.8.6.1. JTAG DTM Registers 3.3.8.6.2. Accessing Debug Module 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 3.4.2.2. Memory Mapped Registers Fields
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. Shadow Register 4.3.3. Arithmetic Logic Unit 4.3.4. Multipy and Divide Units 4.3.5. Floating-Point Unit 4.3.6. Custom Instruction 4.3.7. Instruction Cycles 4.3.8. Reset and Debug Signals 4.3.9. Control and Status Registers 4.3.10. Trap Controller (CLINT) 4.3.11. Trap Controller (CLIC) 4.3.12. Memory and I/O Organization 4.3.13. RISC-V based Debug Module 4.3.14. Error Correction Code (ECC) 4.3.15. Branch Prediction 4.3.16. Lockstep Module
4.3.2. Shadow Register x
4.3.2.1. Shadow Register Implementation 4.3.2.2. Shadow Register Set Management
4.3.2.1. Shadow Register Implementation x
4.3.2.1.1. CLINT 4.3.2.1.2. CLIC with Number of CLIC interrupt levels option 4.3.2.1.3. CLIC with Number of CLIC interrupt levels – 1 Option
4.3.2.2. Shadow Register Set Management x
4.3.2.2.1. Shadow Register File Status CSR (msrfstatus) 4.3.2.2.2. Read Previous Shadow Register CSR (mrdpsrf) 4.3.2.2.3. Write Previous Shadow Register CSR (mwrpsrf)
4.3.5. Floating-Point Unit x
4.3.5.1. IEEE 754 Exception Conditions 4.3.5.2. Floating Point Operations
4.3.5.2. Floating Point Operations x
4.3.5.2.1. Floating Point Classification
4.3.10. Trap Controller (CLINT) x
4.3.10.1. Related Control and Status Register 4.3.10.2. Direct Mode 4.3.10.3. Vectored Mode
4.3.10.1. Related Control and Status Register x
4.3.10.1.1. Machine Status Register (mstatus) 4.3.10.1.2. Machine Trap-Vector Base-Address Register (mtvec) 4.3.10.1.3. Machine Interrupt Register (mip and mie) 4.3.10.1.4. Machine Exception Program Counter Register (mepc) 4.3.10.1.5. Machine Cause Register (mcause) 4.3.10.1.6. Machine Trap Value Register (mtval) 4.3.10.1.7. Machine Second Trap Value Register (mtval2)
4.3.10.2. Direct Mode x
4.3.10.2.1. Hardware Implementation 4.3.10.2.2. Software Implementation
4.3.10.3. Vectored Mode x
4.3.10.3.1. Hardware Implementation 4.3.10.3.2. Software Implementation
4.3.11. Trap Controller (CLIC) x
4.3.11.1. Related Control and Status Register Fields 4.3.11.2. Hardware Implementation 4.3.11.3. Software Implementation
4.3.11.1. Related Control and Status Register Fields x
4.3.11.1.1. CLIC Registers 4.3.11.1.2. Indirect Access M-mode CSRs 4.3.11.1.3. New M-mode CSRs 4.3.11.1.4. Existing CSRs with Changes 4.3.11.1.5. Existing CSRs without Changes
4.3.11.1.1. CLIC Registers x
4.3.11.1.1.1. CLIC Interrupt Attribute (clicintattr) 4.3.11.1.1.2. CLIC Interrupt Input Control (clicintctl) 4.3.11.1.1.3. CLIC Interrupt Pending (clicintip) 4.3.11.1.1.4. CLIC Interrupt Enable clicintie
4.3.11.1.2. Indirect Access M-mode CSRs x
4.3.11.1.2.1. Packing of Indirectly Accessed CLIC Registers 4.3.11.1.2.2. Read/Write clicintctl[i] and clicintattr[i] 4.3.11.1.2.3. Read/Write clicintip[i] and clicintie[i]
4.3.11.1.3. New M-mode CSRs x
4.3.11.1.3.1. Machine Trap-handler Vector Table base address Register (mtvt) 4.3.11.1.3.2. Machine Next Interrupt Handler Address and Interrupt Enable Register (mnxti) 4.3.11.1.3.3. Machine Interrupt Status Register (mintstatus) 4.3.11.1.3.4. Machine Interrupt-Level Threshold Register (mintthresh) 4.3.11.1.3.5. Machine Scratch Swap for Interrupt-Level Register (mscratchcswl)
4.3.11.1.4. Existing CSRs with Changes x
4.3.11.1.4.1. Machine Status Register (mstatus) 4.3.11.1.4.2. Machine Interrupt Register (mie & mip) 4.3.11.1.4.3. Machine Trap-Vector Base-Address Register (mtvec) 4.3.11.1.4.4. Machine Cause Register (mcause)
4.3.11.1.5. Existing CSRs without Changes x
4.3.11.1.5.1. Machine Scratch Register (mscratch) 4.3.11.1.5.2. Machine Exception Program Counter Register (mepc) 4.3.11.1.5.3. Machine Trap Value Register (mtval)
4.3.11.2. Hardware Implementation x
4.3.11.2.1. Asynchronous Interrupt Handling 4.3.11.2.2. Synchronous Exception Handling 4.3.11.2.3. Trap Handling with Pre-emption 4.3.11.2.4. Uninterruptible Critical Section in an Interrupt Handlers 4.3.11.2.5. Returns from Handlers
4.3.11.2.1. Asynchronous Interrupt Handling x
4.3.11.2.1.1. Software-Vectored Interrupt Handling 4.3.11.2.1.2. Hardware-Vectored Interrupt Handling
4.3.12. Memory and I/O Organization x
4.3.12.1. Instruction and Data Buses 4.3.12.2. Address Map 4.3.12.3. Cache Memory 4.3.12.4. Tightly Coupled Memory
4.3.12.1. Instruction and Data Buses x
4.3.12.1.1. Instruction Manager Port 4.3.12.1.2. Data Manager Port
4.3.12.3. Cache Memory x
4.3.12.3.1. Instruction Cache 4.3.12.3.2. Data Cache 4.3.12.3.3. Configurable Cache Memory 4.3.12.3.4. Bypassing Cache (Peripheral Region) 4.3.12.3.5. Using Cache Memory Effectively
4.3.12.4. Tightly Coupled Memory x
4.3.12.4.1. Instruction and Data Tightly Coupled Memory 4.3.12.4.2. Accessing Tightly Coupled Memory 4.3.12.4.3. Using Tightly Coupled Memory Effectively
4.3.13. RISC-V based Debug Module x
4.3.13.1. Debug Module 4.3.13.2. Abstract Commands 4.3.13.3. Program Buffer 4.3.13.4. Debug Mode 4.3.13.5. Hardware Trigger Module 4.3.13.6. JTAG Debug Transport Module 4.3.13.7. Nios® V Processor Implementation
4.3.13.1. Debug Module x
4.3.13.1.1. Reset/Halt/Run Control 4.3.13.1.2. Hart States 4.3.13.1.3. Debug Module Register
4.3.13.2. Abstract Commands x
4.3.13.2.1. Access Register Command 4.3.13.2.2. Using Access Register Command
4.3.13.3. Program Buffer x
4.3.13.3.1. Using Program Buffer
4.3.13.4. Debug Mode x
4.3.13.4.1. Enter Debug Mode 4.3.13.4.2. Exit Debug Mode 4.3.13.4.3. Core Debug Registers
4.3.13.5. Hardware Trigger Module x
4.3.13.5.1. Trigger Registers 4.3.13.5.2. Type of Address/Data Match Triggers 4.3.13.5.3. Using Triggers
4.3.13.6. JTAG Debug Transport Module x
4.3.13.6.1. JTAG DTM Registers 4.3.13.6.2. Accessing Debug Module Interface
4.3.14. Error Correction Code (ECC) x
4.3.14.1. ECC Interface 4.3.14.2. ECC Error Injection 4.3.14.3. Affected CSR during ECC Event
4.4. Programming Model x
4.4.1. Privilege Levels 4.4.2. Control and Status Registers (CSR) Mapping (CLINT) 4.4.3. Control and Status Registers (CSR) Mapping (CLIC)
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 (CLINT) x
4.4.2.1. Control and Status Register Field (CLINT) 4.4.2.2. Memory Mapped Registers Fields
4.4.3. Control and Status Registers (CSR) Mapping (CLIC) x
4.4.3.1. Control and Status Register Fields (CLIC) 4.4.3.2. Memory Mapped Registers Fields 4.4.3.3. CLIC Control and Status Registers Fields
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

3.3.7.1.1. Instruction Manager Port

Nios® V/m processor instruction bus is implemented as a 32-bit AMBA* 4 AXI-Lite manager port as default interface. You can switch it to Avalon® memory-mapped interface for smaller logic utilization.

The instruction manager port:
  • Performs a single function: it fetches instructions to be executed by the processor.
  • Does not perform any write operations.
  • Can issue successive read requests before data return from prior requests.
  • Can prefetch sequential instructions.
  • Always retrieves 32-bit of data. Every instruction fetch returns a full instruction word, regardless of the width of the target memory. The widths of memory in the Nios® V/m processor system is not applicable to the programs. Instruction address is always aligned to a 32-bit word boundary.
  • Does not require any burst adapter because it is non-bursting.
Table 40.  AMBA* 4 AXI-Lite Instruction Interface Signals
Interface Signal Role Width Direction
Write Address Channel awaddr Unused [31:0] Output
awprot Unused [2:0] Output
awvalid Unused 1 Output
awready Unused 1 Input
Write Data Channel wdata Unused [31:0] Output
wstrb Unused [3:0] Output
wvalid Unused 1 Output
wready Unused 1 Input
Write Response Channel bresp Unused [1:0] Input
bvalid Unused 1 Input
bready Unused 1 Output
Read Address Channel araddr

Instruction Address

(Program Counter)

 [31:0] Output
arprot Unused [2:0] Output
arvalid Instruction address valid 1 Output
arready

Instruction address ready

(from memory)

 1 Input
Read Data Channel rdata Instruction [31:0] Input
rresp Instruction response: Non-zero value denotes instruction access fault exception [1:0] Input
rvalid Instruction valid 1 Input
rready Constant 1 1 Output
Table 41.   Avalon® Memory-Mapped Instruction Interface Signals
Signal Role Width Direction
readdata Instruction [31:0] Agent → Processor
waitrequest Force the processor to wait until the agent is ready 1 Agent → Processor
readdatavalid Instruction is valid 1 Agent → Processor
response Instruction response: Non-zero value denotes instruction access fault exception [31:0] Agent → Processor
address

Instruction Address

(Program Counter)

 [31:0] Processor → Agent
read Asserted to indicate a read transfer. 1 Processor → Agent
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