Nios® V Processor Reference Manual

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ID 683632
Date 3/28/2022
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Document Table of Contents
Document Table of Contents x
1. About this Document 2. Nios® V/m Processor 3. Document Revision History for the Nios® V Processor Reference Manual
1. About this Document x
1.1. Overview
2. Nios® V/m 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. Control and Status Registers 2.3.4. Exception Controller 2.3.5. Interrupt Controller 2.3.6. Memory and I/O Organization 2.3.7. RISC-V based Debug Module
2.3.5. Interrupt Controller x
2.3.5.1. Timer and Software Interrupt Module
2.3.6. Memory and I/O Organization x
2.3.6.1. Instruction and Data Buses
2.3.6.1. Instruction and Data Buses x
2.3.6.1.1. Instruction Manager Port 2.3.6.1.2. Data Manager Port 2.3.6.1.3. Address Map
2.3.7. RISC-V based Debug Module x
2.3.7.1. Debug Mode 2.3.7.2. Halt from Debug Module 2.3.7.3. Debug Implementation 2.3.7.4. Abstract Commands in Debug Mode 2.3.7.5. Hardware/Software Interface
2.4. Programming Model x
2.4.1. Privilege Levels 2.4.2. Control and Status Registers (CSR) Mapping
2.4.1. Privilege Levels x
2.4.1.1. Machine Mode (M-mode) 2.4.1.2. Debug Mode (D-mode)
2.4.2. Control and Status Registers (CSR) Mapping x
2.4.2.1. Control and Status Register Field
2.5. Core Implementation x
2.5.1. Instruction Set Reference
1. About this Document
2. Nios® V/m Processor
3. Document Revision History for the Nios® V Processor Reference Manual

2.3.7.4. Abstract Commands in Debug Mode

Nios® V/m processor implements Access Register abstract command. The Access Register command allows read-write access to the processor registers including GPRs, CSRs, FP registers and Program Counter. The Access Register also allows program execution from program buffer. The debugger executes Access Register commands by writing into Abstract Command (command) register using the Access Register command encoding.

Table 10.  Access Register Command Encoding
Bit Field
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
cmdtype 0 aarsize aarpostincrement postexec transfer write
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
regno
Table 11.  Fields Descriptions
Field Role
cmdtype Determine command type

0 : Indicates Access Register command.
aarsize Specifies size of register access

2: Access the lowest 32 bit of register

3: Access the lowest 64 bit of register

4: Access the lowest 128 bit of register
aarpostincrement 0: No effect

1: regno is incremented after successful register access
postexec

0: No effect

1: Execute program in program buffer
transfer

Acts in conjunction with write field.

0: Ignore value in write field

1: Execute operation specified by write field.
write

0: Copy data from register

1: Copy data to register
regno Register address to be accessed.
Note: The Nios V/m processor does not support abstract commands when hardware thread is not halted.
Table 12.  Software Response to Unimplemented Commands
Field State
cmderr[10:8] 0 No error
1 Busy
2 Command not supported
3 Exception - from program buffer instruction
4 Command not executed because hart unavailable, or not in correct state to execute command.
5 Abstract command failed due to bus error
6 RSVD
7 Command failed for other reasons.
Debug Module has the Abstract Control and Status CSR which includes the cmderr field. The cmderr field represents the current state of abstract command being executed. If the cmderr field is non-zero, writes to the command register are ignored. To clear the cmderr field, write 1 for every bit in the field.
Figure 4. Debug Module Interface Signals

Avalon® memory-mapped interface implement the Register Access using request/response bus with Debug Module being the initiator and core being the responder. Address bus carries the register ID.

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