Nios® II Processor Reference Guide

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ID 683836
Date 8/28/2023
Public
Document Table of Contents
Document Table of Contents x
Product Discontinuance Notification 1. Introduction 2. Processor Architecture 3. Programming Model 4. Instantiating the Nios® II Processor 5. Nios® II Core Implementation Details 6. Nios® II Processor Versions 7. Application Binary Interface 8. Instruction Set Reference
1. Introduction x
1.1. Nios® II Processor System Basics 1.2. Getting Started with the Nios II Processor 1.3. Customizing Nios® II Processor Designs 1.4. Configurable Soft Processor Core Concepts 1.5. Intel® FPGA IP Evaluation Mode 1.6. Introduction Revision History
1.4. Configurable Soft Processor Core Concepts x
1.4.1. Configurable Soft Processor Core 1.4.2. Flexible Peripheral Set and Address Map 1.4.3. Automated System Generation
1.4.2. Flexible Peripheral Set and Address Map x
1.4.2.1. Standard Peripherals 1.4.2.2. Custom Components 1.4.2.3. Custom Instructions
2. Processor Architecture x
2.1. Processor Implementation 2.2. Register File 2.3. Arithmetic Logic Unit 2.4. Reset and Debug Signals 2.5. Exception and Interrupt Controllers 2.6. Memory and I/O Organization 2.7. JTAG Debug Module 2.8. Processor Architecture Revision History
2.3. Arithmetic Logic Unit x
2.3.1. Unimplemented Instructions 2.3.2. Custom Instructions
2.5. Exception and Interrupt Controllers x
2.5.1. Exception Controller 2.5.2. EIC Interface 2.5.3. Internal Interrupt Controller
2.6. Memory and I/O Organization x
2.6.1. Instruction and Data Buses 2.6.2. Cache Memory 2.6.3. Tightly-Coupled Memory 2.6.4. Address Map 2.6.5. Memory Management Unit 2.6.6. Memory Protection Unit
2.6.1. Instruction and Data Buses x
2.6.1.1. Memory and Peripheral Access 2.6.1.2. Instruction Master Port 2.6.1.3. Data Master Port 2.6.1.4. Shared Memory for Instructions and Data
2.6.2. Cache Memory x
2.6.2.1. Configurable Cache Memory Options 2.6.2.2. Effective Use of Cache Memory 2.6.2.3. Cache Bypass Methods
2.6.2.3. Cache Bypass Methods x
2.6.2.3.1. I/O Load and Store Instructions Method 2.6.2.3.2. The Bit-31 Cache Bypass Method 2.6.2.3.3. Peripheral Region
2.6.3. Tightly-Coupled Memory x
2.6.3.1. Accessing Tightly-Coupled Memory 2.6.3.2. Effective Use of Tightly-Coupled Memory
2.7. JTAG Debug Module x
2.7.1. JTAG Target Connection 2.7.2. Download and Execute Software 2.7.3. Software Breakpoints 2.7.4. Hardware Breakpoints 2.7.5. Hardware Triggers 2.7.6. Trace Capture
2.7.5. Hardware Triggers x
2.7.5.1. Armed Triggers 2.7.5.2. Triggering on Ranges of Values
2.7.6. Trace Capture x
2.7.6.1. Execution vs. Data Trace 2.7.6.2. Trace Frames
3. Programming Model x
3.1. Operating Modes 3.2. Memory Management Unit 3.3. Memory Protection Unit 3.4. Registers 3.5. Working with the MPU 3.6. Working with ECC 3.7. Exception Processing 3.8. Memory and Peripheral Access 3.9. Instruction Set Categories 3.10. Programming Model Revision History
3.1. Operating Modes x
3.1.1. Supervisor Mode 3.1.2. User Mode
3.2. Memory Management Unit x
3.2.1. Recommended Usage 3.2.2. Memory Management 3.2.3. Address Space and Memory Partitions 3.2.4. TLB Organization 3.2.5. TLB Lookups
3.2.2. Memory Management x
3.2.2.1. Virtual Addressing 3.2.2.2. Memory Protection
3.2.3. Address Space and Memory Partitions x
3.2.3.1. Virtual Memory Address Space 3.2.3.2. Physical Memory Address Space 3.2.3.3. Data Cacheability
3.3. Memory Protection Unit x
3.3.1. Memory Regions 3.3.2. Overlapping Regions 3.3.3. Enabling the MPU
3.3.1. Memory Regions x
3.3.1.1. Base Address 3.3.1.2. Region Type 3.3.1.3. Region Index 3.3.1.4. Region Size or Upper Address Limit 3.3.1.5. Access Permissions 3.3.1.6. Default Cacheability
3.4. Registers x
3.4.1. General-Purpose Registers 3.4.2. Control Registers 3.4.3. Shadow Register Sets
3.4.2. Control Registers x
3.4.2.1. The status Register 3.4.2.2. The estatus Register 3.4.2.3. The bstatus Register 3.4.2.4. The ienable Register 3.4.2.5. The ipending Register 3.4.2.6. The cpuid Register 3.4.2.7. The exception Register 3.4.2.8. The pteaddr Register 3.4.2.9. The tlbacc Register 3.4.2.10. The tlbmisc Register 3.4.2.11. The badaddr Register 3.4.2.12. The config Register 3.4.2.13. The mpubase Register 3.4.2.14. The mpuacc Register
3.4.2.10. The tlbmisc Register x
3.4.2.10.1. The RD Flag 3.4.2.10.2. The WE Flag 3.4.2.10.3. The WAY Field 3.4.2.10.4. The PID Field 3.4.2.10.5. The DBL Flag 3.4.2.10.6. The BAD Flag 3.4.2.10.7. The PERM Flag 3.4.2.10.8. The D Flag
3.4.2.14. The mpuacc Register x
3.4.2.14.1. The MASK Field 3.4.2.14.2. The LIMIT Field 3.4.2.14.3. The MT Flag 3.4.2.14.4. The PERM Field 3.4.2.14.5. The RD Flag 3.4.2.14.6. The WR Flag 3.4.2.14.7. The eccinj Register
3.4.3. Shadow Register Sets x
3.4.3.1. The sstatus Register 3.4.3.2. Initialization with Shadow Register Sets
3.4.3.1. The sstatus Register x
3.4.3.1.1. Changing Register Sets 3.4.3.1.2. Stacks and Shadow Register Sets
3.5. Working with the MPU x
3.5.1. MPU Region Read and Write Operations 3.5.2. MPU Initialization 3.5.3. Debugger Access
3.6. Working with ECC x
3.6.1. Enabling ECC 3.6.2. Handling ECC Errors 3.6.3. Injecting ECC Errors
3.6.1. Enabling ECC x
3.6.1.1. Disabling ECC
3.6.3. Injecting ECC Errors x
3.6.3.1. Instruction Cache Tag RAM 3.6.3.2. Instruction Cache Data RAM 3.6.3.3. ITCMs 3.6.3.4. Register File RAM Blocks 3.6.3.5. Data Cache Tag RAM 3.6.3.6. Data Cache Data RAM (Clean Line) 3.6.3.7. Data Cache Data RAM (Dirty Line) 3.6.3.8. Data Cache Victim Line Buffer RAM 3.6.3.9. DTCMs 3.6.3.10. MMU TLB RAM
3.7. Exception Processing x
3.7.1. Terminology 3.7.2. Exception Overview 3.7.3. Exception Latency 3.7.4. Reset Exceptions 3.7.5. Break Exceptions 3.7.6. Interrupt Exceptions 3.7.7. Instruction-Related Exceptions 3.7.8. Other Exceptions 3.7.9. Exception Processing Flow 3.7.10. Determining the Cause of Interrupt and Instruction-Related Exceptions 3.7.11. Handling Nested Exceptions 3.7.12. Handling Nonmaskable Interrupts 3.7.13. Masking and Disabling Exceptions
3.7.3. Exception Latency x
3.7.3.1. Interrupt Latency
3.7.5. Break Exceptions x
3.7.5.1. Processing a Break 3.7.5.2. Understanding Register Usage 3.7.5.3. Returning From a Break
3.7.6. Interrupt Exceptions x
3.7.6.1. External Interrupt Controller Interface 3.7.6.2. Internal Interrupt Controller
3.7.6.1. External Interrupt Controller Interface x
3.7.6.1.1. Requested Handler Address 3.7.6.1.2. Requested Interrupt Level 3.7.6.1.3. Requested Register Set 3.7.6.1.4. Requested NMI Mode 3.7.6.1.5. Shadow Register Sets
3.7.7. Instruction-Related Exceptions x
3.7.7.1. Trap Instruction 3.7.7.2. Break Instruction 3.7.7.3. Unimplemented Instruction 3.7.7.4. Illegal Instruction 3.7.7.5. Supervisor-Only Instruction 3.7.7.6. Supervisor-Only Instruction Address 3.7.7.7. Supervisor-Only Data Address 3.7.7.8. Misaligned Data Address 3.7.7.9. Misaligned Destination Address 3.7.7.10. Division Error 3.7.7.11. Fast TLB Miss 3.7.7.12. Double TLB Miss 3.7.7.13. TLB Permission Violation 3.7.7.14. MPU Region Violation
3.7.9. Exception Processing Flow x
3.7.9.1. Processing General Exceptions 3.7.9.2. Exception Flow with the EIC Interface 3.7.9.3. Exception Flow with the Internal Interrupt Controller 3.7.9.4. Exceptions and Processor Status
3.7.10. Determining the Cause of Interrupt and Instruction-Related Exceptions x
3.7.10.1. Nios® II/f Exception Processing 3.7.10.2. Nios® II/e Exception Processing
3.7.11. Handling Nested Exceptions x
3.7.11.1. Nested Exceptions with the Internal Interrupt Controller 3.7.11.2. Nested Exceptions with an External Interrupt Controller
3.7.13. Masking and Disabling Exceptions x
3.7.13.1. Disabling Maskable Interrupts 3.7.13.2. Masking Interrupts with an External Interrupt Controller 3.7.13.3. Masking Interrupts with the Internal Interrupt Controller 3.7.13.4. Returning From Interrupt and Instruction-Related Exceptions
3.7.13.4. Returning From Interrupt and Instruction-Related Exceptions x
3.7.13.4.1. Return Address Considerations
3.8. Memory and Peripheral Access x
3.8.1. Cache Memory
3.8.1. Cache Memory x
3.8.1.1. Virtual Address Aliasing
3.9. Instruction Set Categories x
3.9.1. Data Transfer Instructions 3.9.2. Arithmetic and Logical Instructions 3.9.3. Move Instructions 3.9.4. Comparison Instructions 3.9.5. Shift and Rotate Instructions 3.9.6. Program Control Instructions 3.9.7. Other Control Instructions 3.9.8. Custom Instructions 3.9.9. No-Operation Instruction 3.9.10. Potential Unimplemented Instructions
4. Instantiating the Nios® II Processor x
4.1. Main Nios® II Tab 4.2. Vectors Tab 4.3. Caches and Memory Interfaces Tab 4.4. Arithmetic Instructions Tab 4.5. MMU and MPU Settings Tab 4.6. JTAG Debug Tab 4.7. Advanced Features Tab 4.8. The Quartus Prime IP File 4.9. Instantiating the Nios® II Processor Revision History
4.2. Vectors Tab x
4.2.1. Reset Vector 4.2.2. Exception Vector 4.2.3. Fast TLB Miss Exception Vector
4.3. Caches and Memory Interfaces Tab x
4.3.1. Instruction Cache 4.3.2. Flash Accelerator 4.3.3. Data Cache 4.3.4. Tightly-coupled Memories 4.3.5. Peripheral Region
4.4. Arithmetic Instructions Tab x
4.4.1. Arithmetic Instructions 4.4.2. Arithmetic Implementation
4.5. MMU and MPU Settings Tab x
4.5.1. MMU 4.5.2. MPU
4.7. Advanced Features Tab x
4.7.1. ECC 4.7.2. Interrupt Controller Interfaces 4.7.3. Shadow Register Sets 4.7.4. Reset Signals 4.7.5. CPU ID Control Register Value 4.7.6. Generate Trace File 4.7.7. Exception Checking 4.7.8. Branch Prediction 4.7.9. RAM Memory Protection
5. Nios® II Core Implementation Details x
5.1. Device Family Support 5.2. Nios II/f Core 5.3. Nios II/s Core 5.4. Nios II/e Core 5.5. Nios® II Core Implementation Details Revision History
5.2. Nios II/f Core x
5.2.1. Overview 5.2.2. Arithmetic Logic Unit 5.2.3. Memory Access 5.2.4. Tightly-Coupled Memory 5.2.5. Memory Management Unit 5.2.6. Memory Protection Unit 5.2.7. Execution Pipeline 5.2.8. Instruction Performance 5.2.9. Exception Handling 5.2.10. ECC 5.2.11. JTAG Debug Module
5.2.2. Arithmetic Logic Unit x
5.2.2.1. Multiply and Divide Performance 5.2.2.2. Shift and Rotate Performance
5.2.3. Memory Access x
5.2.3.1. Instruction and Data Master Ports 5.2.3.2. Instruction and Data Caches
5.2.3.2. Instruction and Data Caches x
5.2.3.2.1. Instruction Cache 5.2.3.2.2. Data Cache 5.2.3.2.3. Bursting
5.2.5. Memory Management Unit x
5.2.5.1. Micro Translation Lookaside Buffers
5.2.7. Execution Pipeline x
5.2.7.1. Pipeline Stalls 5.2.7.2. Branch Prediction
5.2.9. Exception Handling x
5.2.9.1. External Interrupt Controller Interface
5.3. Nios II/s Core x
5.3.1. Overview 5.3.2. Arithmetic Logic Unit 5.3.3. Memory Access 5.3.4. Tightly-Coupled Memory 5.3.5. Execution Pipeline 5.3.6. Instruction Performance 5.3.7. Exception Handling 5.3.8. JTAG Debug Module
5.3.2. Arithmetic Logic Unit x
5.3.2.1. Multiply and Divide Performance 5.3.2.2. Shift and Rotate Performance
5.3.3. Memory Access x
5.3.3.1. Instruction and Data Master Ports 5.3.3.2. Instruction Cache
5.3.5. Execution Pipeline x
5.3.5.1. Pipeline Stalls 5.3.5.2. Branch Prediction
5.4. Nios II/e Core x
5.4.1. Overview 5.4.2. Arithmetic Logic Unit 5.4.3. Memory Access 5.4.4. Instruction Execution Stages 5.4.5. Instruction Performance 5.4.6. Exception Handling 5.4.7. JTAG Debug Module
6. Nios® II Processor Versions x
6.1. Nios II Versions Revision History 6.2. Architecture Revisions 6.3. Core Revisions 6.4. JTAG Debug Module Revisions 6.5. Nios® II Processor Versions Revision History
6.3. Core Revisions x
6.3.1. Nios II/f Core 6.3.2. Nios II/s Core 6.3.3. Nios II/e Core
7. Application Binary Interface x
7.1. Data Types 7.2. Memory Alignment 7.3. Register Usage 7.4. Stacks 7.5. Arguments and Return Values 7.6. DWARF-2 Definition 7.7. Object Files 7.8. Relocation 7.9. ABI for Linux Systems 7.10. Development Environment 7.11. Application Binary Interface Revision History
7.4. Stacks x
7.4.1. Frame Pointer Elimination 7.4.2. Call Saved Registers 7.4.3. Further Examples of Stacks 7.4.4. Function Prologues
7.4.3. Further Examples of Stacks x
7.4.3.1. Stack Frame for a Function With alloca() 7.4.3.2. Stack Frame for a Function with Variable Arguments 7.4.3.3. Stack Frame for a Function with Structures Passed By Value
7.4.4. Function Prologues x
7.4.4.1. Prologue Variations
7.5. Arguments and Return Values x
7.5.1. Arguments 7.5.2. Return Values
7.9. ABI for Linux Systems x
7.9.1. Linux Toolchain Relocation Information 7.9.2. Linux Function Calls 7.9.3. Linux Operating System Call Interface 7.9.4. Linux Process Initialization 7.9.5. Linux Position-Independent Code Loading the GOT Pointer Small GOT Model Entry for Global Symbols Large GOT Model Entry for Global Symbols Local Symbols for small GOT Model Local Symbols for large GOT Model Small GOT Model entry in PLT GOT Large GOT Model entry in PLT GOT Accessing Function or Variable in Current Shared Object Switch Statement Implemented with Table 7.9.6. Linux Program Loading and Dynamic Linking 7.9.7. Linux Conventions
7.9.1. Linux Toolchain Relocation Information x
7.9.1.1. Copy Relocation 7.9.1.2. Jump Slot Relocation 7.9.1.3. Thread-Local Storage
7.9.6. Linux Program Loading and Dynamic Linking x
7.9.6.1. Global Offset Table 7.9.6.2. Function Addresses 7.9.6.3. Procedure Linkage Table 7.9.6.4. Linux Program Interpreter 7.9.6.5. Linux Initialization and Termination Functions
7.9.7. Linux Conventions x
7.9.7.1. System Calls 7.9.7.2. Userspace Breakpoints 7.9.7.3. Atomic Operations 7.9.7.4. Processor Requirements
8. Instruction Set Reference x
8.1. Word Formats 8.2. Instruction Opcodes 8.3. Assembler Pseudo-Instructions 8.4. Assembler Macros 8.5. Instruction Set Reference 8.6. Instruction Set Reference Revision History
8.1. Word Formats x
8.1.1. I-Type 8.1.2. R-Type 8.1.3. J-Type
8.5. Instruction Set Reference x
8.5.1. add 8.5.2. addi 8.5.3. and 8.5.4. andhi 8.5.5. andi 8.5.6. beq 8.5.7. bge 8.5.8. bgeu 8.5.9. bgt 8.5.10. bgtu 8.5.11. ble 8.5.12. bleu 8.5.13. blt 8.5.14. bltu 8.5.15. bne 8.5.16. br 8.5.17. break 8.5.18. bret 8.5.19. call 8.5.20. callr 8.5.21. cmpeq 8.5.22. cmpeqi 8.5.23. cmpge 8.5.24. cmpgei 8.5.25. cmpgeu 8.5.26. cmpgeui 8.5.27. cmpgt 8.5.28. cmpgti 8.5.29. cmpgtu 8.5.30. cmpgtui 8.5.31. cmple 8.5.32. cmplei 8.5.33. cmpleu 8.5.34. cmpleui 8.5.35. cmplt 8.5.36. cmplti 8.5.37. cmpltu 8.5.38. cmpltui 8.5.39. cmpne 8.5.40. cmpnei 8.5.41. custom 8.5.42. div 8.5.43. divu 8.5.44. eret 8.5.45. flushd 8.5.46. flushda 8.5.47. flushi 8.5.48. flushp 8.5.49. initd 8.5.50. initda 8.5.51. initi 8.5.52. jmp 8.5.53. jmpi 8.5.54. ldb / ldbio 8.5.55. ldbu / ldbuio 8.5.56. ldh / ldhio 8.5.57. ldhu / ldhuio 8.5.58. ldw / ldwio 8.5.59. mov 8.5.60. movhi 8.5.61. movi 8.5.62. movia 8.5.63. movui 8.5.64. mul 8.5.65. muli 8.5.66. mulxss 8.5.67. mulxsu 8.5.68. mulxuu 8.5.69. nextpc 8.5.70. nop 8.5.71. nor 8.5.72. or 8.5.73. orhi 8.5.74. ori 8.5.75. rdctl 8.5.76. rdprs 8.5.77. ret 8.5.78. rol 8.5.79. roli 8.5.80. ror 8.5.81. sll 8.5.82. slli 8.5.83. sra 8.5.84. srai 8.5.85. srl 8.5.86. srli 8.5.87. stb / stbio l 8.5.88. sth / sthio 8.5.89. stw / stwio 8.5.90. sub 8.5.91. subi 8.5.92. sync 8.5.93. trap 8.5.94. wrctl 8.5.95. wrprs 8.5.96. xor 8.5.97. xorhi 8.5.98. xori
Product Discontinuance Notification
1. Introduction
2. Processor Architecture
3. Programming Model
4. Instantiating the Nios® II Processor
5. Nios® II Core Implementation Details
6. Nios® II Processor Versions
7. Application Binary Interface
8. Instruction Set Reference

7.9.5. Linux Position-Independent Code

Every position-independent code (PIC) function which uses global data or global functions must load the value of the GOT pointer into a register. Any available register may be used. If a caller-saved register is used the function must save and restore it around calls. If a callee-saved register is used it must be saved and restored around the current function. Examples in this document use r22 for the GOT pointer.

The GOT pointer is loaded using a PC-relative offset to the _gp_got symbol, as shown below.

Loading the GOT Pointer

nextpc r22
1:
   orhi r1, %hiadj(_gp_got - 1b) # R_NIOS2_PCREL_HA _gp_got
   addi r1, r1, %lo(_gp_got - 1b) # R_NIOS2_PCREL_LO _gp_got - 4  
   add r22, r22, r1
   # GOT pointer in r22

Data may be accessed by loading its location from the GOT. A single word GOT entry is generated for each referenced symbol.

Small GOT Model Entry for Global Symbols

addi   r3, r22, %got(x)      # R_NIOS2_GOT16

GOT[n]                         R_NIOS2_GLOB_DAT x

Large GOT Model Entry for Global Symbols

movhi r3,     %got_hiadj(x)    # R_NIOS2_GOT_HA
addi  r3, r3, %got_lo(x)       # R_NIOS2_GOT_LO
add   r3, r3, r22

GOT[n]                           R_NIOS2_GLOB_DAT x

For local symbols, the symbolic reference to x is replaced by a relative relocation against symbol zero, with the link time address of x as an addend, as shown in the example below.

Local Symbols for small GOT Model

addi   r3, r22, %got(x)         # R_NIOS2_GOT16

GOT[n]                            R_NIOS2_RELATIVE +x

Local Symbols for large GOT Model

movhi r3,     %got_hiadj(x)     # R_NIOS2_GOT_HA
addi  r3, r3, %got_lo(x)        # R_NIOS2_GOT_LO
add   r3, r3, r22

GOT[n]                            R_NIOS2_RELATIVE +x

The call and jmpi instructions are not available in position-independent code. Instead, all calls are made through the GOT. Function addresses may be loaded with %call, which allows lazy binding. To initialize a function pointer, load the address of the function with %got instead. If no input object requires the address of the function its GOT entry is placed in the PLT GOT for lazy binding, as shown in the example below.

For information about the PLT, refer to the "Procedure Linkage Table" section.

Small GOT Model entry in PLT GOT

ldw      r3, %call(fun)(r22)      # R_NIOS2_CALL16 fun
callr    r3

PLTGOT[n]                           R_NIOS_JUMP_SLOT fun

Large GOT Model entry in PLT GOT

movhi r3,     %call_hiadj(x)     # R_NIOS2_CALL_HA
addi  r3, r3, %call_lo(x)        # R_NIOS2_CALL_LO
add   r3, r3, r22
ldw   r3, 0(r3)
callr r3

PLTGOT[n]                           R_NIOS_JUMP_SLOT fun

When a function or variable resides in the current shared object at compile time, it can be accessed via a PC-relative or GOT-relative offset, as shown below.

Accessing Function or Variable in Current Shared Object

orhi      r3, %gotoff_hiadj(x)       # R_NIOS2_GOTOFF_HA x
addi      r3, r3, %gotoff_lo(x)      # R_NIOS2_GOTOFF_LO x
add       r3, r22, r3
# Address of x in r3

Multiway branches such as switch statements can be implemented with a table of GOT-relative offsets, as shown below.

Switch Statement Implemented with Table

# Scaled table offset in r4
   orhi      r3, %gotoff_hiadj(Ltable)       # R_NIOS2_GOTOFF_HA Ltable
   addi      r3, r3, %gotoff_lo(Ltable)      # R_NIOS2_GOTOFF_LO Ltable
   add       r3, r22, r3                     # r3 == &Ltable
   add       r3, r3, r4
   ldw       r4, 0(r3)                       # r3 == Ltable[index]
   add       r4, r4, r22                     # Convert offset into destination   
   jmp       r4
   ...
Ltable:
   .word %gotoff(Label1)
   .word %gotoff(Label2)
   .word %gotoff(Label3)
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