Nios® V Processor Reference Manual

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ID 683632
Date 1/27/2025
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. Instruction Cycles 2.3.5. Memory and I/O Organization 2.3.6. Error Correction Code (ECC)
2.3.5. Memory and I/O Organization x
2.3.5.1. Instruction and Data Buses 2.3.5.2. Address Map
2.3.5.1. Instruction and Data Buses x
2.3.5.1.1. Instruction Manager Port 2.3.5.1.2. Data Manager Port 2.3.5.1.3. 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. 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. Arithmetic Logic Unit 4.3.3. Multipy and Divide Units 4.3.4. Floating-Point Unit 4.3.5. Custom Instruction 4.3.6. Instruction Cycles 4.3.7. Reset and Debug Signals 4.3.8. Control and Status Registers 4.3.9. Trap Controller (CLINT) 4.3.10. Memory and I/O Organization 4.3.11. RISC-V based Debug Module 4.3.12. Error Correction Code (ECC) 4.3.13. Branch Prediction 4.3.14. 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
4.3.9. Trap Controller (CLINT) x
4.3.9.1. Related Control and Status Register 4.3.9.2. Direct Mode 4.3.9.3. Vectored Mode
4.3.9.1. Related Control and Status Register x
4.3.9.1.1. Machine Status Register (mstatus) 4.3.9.1.2. Machine Trap-Vector Base-Address Register (mtvec) 4.3.9.1.3. Machine Interrupt Register (mip and mie) 4.3.9.1.4. Machine Exception Program Counter Register (mepc) 4.3.9.1.5. Machine Cause Register (mcause) 4.3.9.1.6. Machine Trap Value Register (mtval) 4.3.9.1.7. Machine Second Trap Value Register (mtval2)
4.3.9.2. Direct Mode x
4.3.9.2.1. Hardware Implementation 4.3.9.2.2. Software Implementation
4.3.9.3. Vectored Mode x
4.3.9.3.1. Hardware Implementation 4.3.9.3.2. Software Implementation
4.3.10. Memory and I/O Organization x
4.3.10.1. Instruction and Data Buses 4.3.10.2. Address Map 4.3.10.3. Cache Memory 4.3.10.4. Tightly Coupled Memory
4.3.10.1. Instruction and Data Buses x
4.3.10.1.1. Instruction Manager Port 4.3.10.1.2. Data Manager Port
4.3.10.3. Cache Memory x
4.3.10.3.1. Instruction Cache 4.3.10.3.2. Data Cache 4.3.10.3.3. Configurable Cache Memory 4.3.10.3.4. Bypassing Cache (Peripheral Region) 4.3.10.3.5. Using Cache Memory Effectively
4.3.10.4. Tightly Coupled Memory x
4.3.10.4.1. Instruction and Data Tightly Coupled Memory 4.3.10.4.2. Accessing Tightly Coupled Memory 4.3.10.4.3. Using Tightly Coupled Memory Effectively
4.3.11. RISC-V based Debug Module x
4.3.11.1. Debug Module 4.3.11.2. Abstract Commands 4.3.11.3. Program Buffer 4.3.11.4. Debug Mode 4.3.11.5. Hardware Trigger Module 4.3.11.6. JTAG Debug Transport Module 4.3.11.7. Nios® V Processor Implementation
4.3.11.1. Debug Module x
4.3.11.1.1. Reset/Halt/Run Control 4.3.11.1.2. Hart States 4.3.11.1.3. Debug Module Register
4.3.11.2. Abstract Commands x
4.3.11.2.1. Access Register Command 4.3.11.2.2. Using Access Register Command
4.3.11.3. Program Buffer x
4.3.11.3.1. Using Program Buffer
4.3.11.4. Debug Mode x
4.3.11.4.1. Enter Debug Mode 4.3.11.4.2. Exit Debug Mode 4.3.11.4.3. Core Debug Registers
4.3.11.5. Hardware Trigger Module x
4.3.11.5.1. Trigger Registers 4.3.11.5.2. Type of Address/Data Match Triggers 4.3.11.5.3. Using Triggers
4.3.11.6. JTAG Debug Transport Module x
4.3.11.6.1. JTAG DTM Registers 4.3.11.6.2. Accessing Debug Module Interface
4.3.12. Error Correction Code (ECC) x
4.3.12.1. ECC Interface 4.3.12.2. ECC Error Injection 4.3.12.3. 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)
4.4.1. 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
4.5. 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

4.4.2.1. Control and Status Register Field (CLINT)

The value in the each CSR registers determines the state of the Nios® V/g processor. The field descriptions are based on the RISC-V specification.

All CSRs can be accessed by using csrr* instruction in Machine mode except for the Debug mode registers (0x7B0 and 0x7B1) which can only be accessed through Debug mode.

Table 143.  Floating-Point CSR Register FieldsThe fcsr CSR is a 32-bit read/write register that holds the accrued exception flags.

RISC-V CSR instructions can access fflags and frm field individually by specifying the CSR address (0x001 and 0x002) respectively.

When accessing frm field individually using the CSR address 0x002, the rounding mode is transferred as bits [2:0] of the destination register.

RNE (000) is the only supporting rounding mode. Writing other rounding mode into frm generates an illegal instruction exception.

Bit Field
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Reserved
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Reserved

Rounding Mode

(frm)

Accrued Exceptions (fflags)
000 NV DZ OF UF NX
Table 144.  Machine Status Register FieldsThe mstatus register is a 32-bit read-write register that keeps track of and controls the hart’s current operating state.
Bit Field
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
SD 0 0 0 0 0 0 0 0
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
0 FS[1:0] MPP[1:0] 0 0 MPIE 0 0 0 MIE 0 0 0
The following bitfields are read-only 0:
  • Bit 22 (TSR = 0): S-mode is not supported
  • Bit 21 (TW = 0): There are no modes less privileged than M-mode.
  • Bit 20 (TVM = 0): S-mode is not supported
  • Bit 19 (MXR = 0): S-mode is not supported
  • Bit 18 (SUM = 0): S-mode and U-mode are not supported
  • Bit 17 (MPRV = 0): U-mode is not supported
  • Bit 16 and Bit 15 (XS[1:0] = 0): S-mode is not supported
  • Bit 10 and Bit 9 (VS[1:0] = 0): S-mode is not supported
  • Bit 8 (SPP = 0): S-mode is not supported
  • Bit 6 (UBE = 0): U-mode is not supported
  • Bit 5 (SPIE = 0): S-mode is not supported
  • Bit 1 (SIE = 0): S-mode is not supported
Table 145.  Machine ISA Register FieldsThe misa CSR is a read-write register reporting the ISA supported by the hart.
Bit Field
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
MXL[1:0] 0 Extension[25:0]
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Extension[25:0]
Table 146.  Machine Interrupt-Enable Register FieldsThe mie register is a 32-bit read-write register that contains interrupt enable bits. This core does not support supervisor or user modes. Thus, any interrupt related to these modes is read-only 0.
Bit Field
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Platform Interrupt[15:0]
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
0 MEIE 0 0 0 MTIE 0 0 0 MSIE 0 0 0
Table 147.  Machine Trap-Handler Base Address Register FieldsThe mtvec register is a 32-bit read/write register that holds trap vector configuration, consisting of a vector base address (BASE) and a vector mode (MODE).
Bit Field
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Base[31:2]
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Base[31:2] Mode
Table 148.  Machine Exception Program Counter Register FieldsThe mepc register is a 32-bit read-write register that holds the addresses of the instruction that was interrupted or that encountered the exception when a trap is taken into M-mode.
Bit Field
31 30 29 28 27 26 25 ... 6 5 4 3 2 1 0
mepc
Table 149.  Machine Trap Cause Register FieldsThe mcause register is a 32-bit read-write register that hold the code indicating the event that caused the trap when a trap is taken into M-mode.
Bit Field
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Interrupt Exception code [30:16]
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Exception code [15:0]
Table 150.  Machine Trap Value Register Fields The mtval register is a 32-bit read-write register that is written with exception-specific information to assist software in handling the trap when a trap is taken into M-mode.
Bit Field
31 30 29 28 27 26 25 ... 6 5 4 3 2 1 0
mtval
Table 151.  Machine Interrupt-Pending Register FieldsThe mip register is a 32-bit read/write register containing information on pending interrupts. This core does not support supervisor or user modes. Thus, any interrupt related to these modes is read-only 0.
Bit Field
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Platform Interrupt[15:0]
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
0 MEIP 0 0 0 MTIP 0 0 0 MSIP 0 0 0
Table 152.  Trigger Select Register FieldsThe tselect register is a 32-bit read/write register that selects the current trigger is accessible by other trigger register.
Bit Field
31 30 29 28 27 26 25 ... 6 5 4 3 2 1 0
tselect
Table 153.  Machine Trap Value 2 Register FieldsThe mtval2 register is a 32-bit read-write register that is written with exception-specific information to assist software in handling the trap when a trap is taken into M-mode.

This core does not support hypervisor mode. Thus, the Nios® V/g processor implements this register for ECC exception only (No implementation on guest-page faults).

Bit Field
31 30 29 28 27 26 25 … 6 5 4 3 2 1 0
mtval2
Table 154.  Trigger Data 1 (Match Control) Register FieldsThe tdata1 (mcontrol) register is a 32-bit read/write register containing information on the trigger type, tdata registers accessibility, and trigger implementation. This core does not support supervisor or user modes. Thus, any bitfield related to these modes is read-only 0.
Bit Field
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
type=2 dmode maskmax hit select timing sizelo
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
action chain match m 0 0 0 execute store load
Table 155.  Trigger Data 2 Register FieldsThe tdata2 register is a 32-bit read/write register containing the trigger-specific data.
Bit Field
31 30 29 28 27 26 25 … 6 5 4 3 2 1 0
tdata2
Table 156.  Trigger Info Register FieldsThe tinfo register is a 32-bit read-only register containing information on each possible tdata1.type.
Bit Field
31 30 29 … 18 17 16 15 14 13 … 2 1 0
0 info
Table 157.  Debug Control and Status Register FieldsThe dcsr CSR is a 32-bit read-write register containing information and status during D-mode. This core does not support supervisor or user modes. Thus, any bitfield related to these modes is read-only 0.
Bit Field
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
debugver 0
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ebreakm 0 0 0 stepie stopcount stoptime cause 0 mprven nmip step prv
Table 158.  Debug Program Counter Register FieldsUpon entry to D-mode, dpc CSR is updated with the virtual address of the next instruction to be executed.
Bit Field
31 30 29 28 27 26 25 ... 6 5 4 3 2 1 0
dpc
Table 159.  Vendor ID Register FieldsThe mvendorid CSR is a 32-bit read-only register that provides the JEDEC manufacturer ID of the provider of the core.
Bit Field
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Bank
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Bank Offset
Table 160.  Architecture ID Register FieldsThe marchid CSR is a 32-bit read-only register encoding the base microarchitecture of the hart.
Bit Field
31 30 29 28 27 26 25 ... 6 5 4 3 2 1 0
Architecture ID
Table 161.  Implementation ID Register FieldsThe mimpid CSR provides a unique encoding of the version of the processor implementation.
Bit Field
31 30 29 28 27 26 25 ... 6 5 4 3 2 1 0
Implementation
Table 162.  Hardware Thread ID Register FieldsThe mhartid CSR is a 32-bit read-only register that contains the integer ID of the hardware thread running the code
Bit Field
31 30 29 28 27 26 25 ... 6 5 4 3 2 1 0
Hart ID
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