Nios II Classic Processor Reference Guide

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ID 683620
Date 10/28/2016
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Document Table of Contents
Document Table of Contents x
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 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
2.6.3. 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 C Flag 3.4.2.14.4. The MT Flag 3.4.2.14.5. The PERM Field 3.4.2.14.6. The RD Flag 3.4.2.14.7. The WR Flag 3.4.2.14.8. 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. Register File RAM Blocks 3.6.3.4. 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. Handling Nested Exceptions 3.7.11. Handling Nonmaskable Interrupts 3.7.12. 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. Handling Nested Exceptions x
3.7.10.1. Nested Exceptions with the Internal Interrupt Controller 3.7.10.2. Nested Exceptions with an External Interrupt Controller
3.7.12. Masking and Disabling Exceptions x
3.7.12.1. Disabling Maskable Interrupts 3.7.12.2. Masking Interrupts with an External Interrupt Controller 3.7.12.3. Masking Interrupts with the Internal Interrupt Controller 3.7.12.4. Returning From Interrupt and Instruction-Related Exceptions
3.7.12.4. Returning From Interrupt and Instruction-Related Exceptions x
3.7.12.4.1. 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. Core Nios II Tab 4.2. Caches and Memory Interfaces Tab 4.3. Advanced Features Tab 4.4. MMU and MPU Settings Tab 4.5. JTAG Debug Module Tab 4.6. Custom Instruction Tab 4.7. The Quartus Prime IP File 4.8. Document Revision History
4.1. Core Nios II Tab x
4.1.1. Core Selection 4.1.2. Multiply and Divide Settings 4.1.3. Reset Vector 4.1.4. General Exception Vector 4.1.5. Memory Management Unit Settings 4.1.6. Memory Protection Unit Settings
4.1.5. Memory Management Unit Settings x
4.1.5.1. Fast TLB Miss Exception Vector
4.2. Caches and Memory Interfaces Tab x
4.2.1. Instruction Master Settings 4.2.2. Data Master Settings
4.3. Advanced Features Tab x
4.3.1. Reset Signals 4.3.2. Control Registers 4.3.3. Exception Checking 4.3.4. Interrupt Controller Interfaces 4.3.5. Shadow Register Sets 4.3.6. HardCopy Compatible 4.3.7. ECC
4.4. MMU and MPU Settings Tab x
4.4.1. MMU 4.4.2. MPU
4.5. JTAG Debug Module Tab x
4.5.1. Debug Level Settings 4.5.2. Debug Signals 4.5.3. Break Vector 4.5.4. Advanced Debug Settings
4.6. Custom Instruction Tab x
4.6.1. Altera-Provided Custom Instructions
4.6.1. Altera-Provided Custom Instructions x
4.6.1.1. Floating Point Hardware 2 Custom Instruction 4.6.1.2. Floating-Point Hardware Custom Instruction 4.6.1.3. Bitswap Custom Instruction
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 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
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

3.4.1. General-Purpose Registers

The Nios II architecture provides thirty-two 32-bit general-purpose registers, r0 through r31. Some registers have names recognized by the assembler. For example, the zero register (r0) always returns the value zero, and writing to zero has no effect. The ra register (r31) holds the return address used by procedure calls and is implicitly accessed by the call, callr and ret instructions. C and C++ compilers use a common procedure-call convention, assigning specific meaning to registers r1 through r23 and r26 through r28.

Table 11.  The Nios II General-Purpose Registers
Register Name Function Register Name Function
r0 zero 0x00000000 r16   Callee-saved register
r1 at Assembler temporary r17   Callee-saved register
r2   Return value r18   Callee-saved register
r3   Return value r19   Callee-saved register
r4   Register arguments r20   Callee-saved register
r5   Register arguments r21   Callee-saved register
r6   Register arguments r22   Callee-saved register
r7   Register arguments r23   Callee-saved register
r8   Caller-saved register r24 et Exception temporary
r9   Caller-saved register r25 bt Breakpoint temporary
r10   Caller-saved register r26 gp Global pointer
r11   Caller-saved register r27 sp Stack pointer
r12   Caller-saved register r28 fp Frame pointer
r13   Caller-saved register r29 ea Exception return address
r14   Caller-saved register r30 sstatus Status register
r15   Caller-saved register r31 ra Return address
Note: r25 is used exclusively by the JTAG debug module. It is used as the breakpoint temporary (bt) register in the normal register set. In shadow register sets, r25 is reserved.
Note: r30 is used as the breakpoint return address (ba) in the normal register set, and as the shadow register set status (sstatus) in each shadow register set. For details about sstatus, refer to The Status Register section.

For more information, refer to the Application Binary Interface chapter of the Nios® II Processor Reference Handbook.

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