Nios® V Processor Reference Manual

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ID 683632
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

4.3.11.1. Related Control and Status Register Fields

The Nios® V processor only supports Machine-Level Control and Status Registers (CSRs) because it operates only in Machine Mode (M-mode). It is the primary privileged level and has low-level access to the machine implementation.

When you enable CLIC, it introduces new indirect access M-mode CSRs and new M-mode CSRs into the Nios® V processor. Additionally, it changes some existing CSRs that were based on CLINT specifications to meet CLIC specifications.

Table 118.   Machine Mode CSRs related to CLIC
Number Name From CLINT to CLIC Description
0x300 mstatus MODIFIED Status register
0x304 mie INACTIVE Interrupt-enable register
0x305 mtvec MODIFIED Trap-handler base address / interrupt mode
0x307 mtvt NEW Trap-handler vector table base address
0x340 mscratch NO CHANGE Scratch register for trap handlers
0x341 mepc NO CHANGE Exception program counter
0x342 mcause MODIFIED Cause of trap
0x343 mtval NO CHANGE Bad address or instruction
0x344 mip INACTIVE Interrupt-pending register
0x345 mnxti NEW Interrupt handler address and enable modifier
0x347 mintthresh NEW Interrupt-level threshold
0x349 mscratchcswl NEW Conditional scratch swap on level change
0x350 miselect NEW Machine Indirect Select
0x351 mireg NEW Machine Indirect Alias
0x352 mireg2 NEW Machine Indirect Alias 2
0xFB1 mintstatus NEW Current interrupt levels

In the Nios® V processor, you can switch between CLINT and CLIC mode using the mtvec register. Thus, it is important to recognize which CSRs—CLINT CSRs or CLIC CSRs, are accessible after the switch is complete. Accessing CLIC CSRs in CLINT mode causes the processor to report illegal instruction exception, except for the mintstatus register. However, note that the mintstatus register is irrelevant in CLINT mode.


Section Content
CLIC Registers
Indirect Access M-mode CSRs
New M-mode CSRs
Existing CSRs with Changes
Existing CSRs without Changes

Related Information
Level Two Title