basic_RV32s

basic_RV32s is a framework for learning Processor design with RISC-V RV32I ISA (Instruction Set Architecture).
It provides step-by-step guideline for designing processor from single-cycle processor to 5 Stage Pipelined with Exception Handling.

Introduction

KHWL

I've always wondered how to make CPU and I wanted to make my own.
Although it was a far dream for me, I gave it a try when I was serving the Korean Military duty. And made the result pretty legitimately.

^{Signal-Level Block Diagram of RV32I46F_5SP Core}

While designing the Architecture of processor, I've felt the gap between the theories and actual implementations at certain point and it took a long way to discover the problem and resolve it.

So I decided to make this project for academic/instructional purposes so that anyone who wants to make & design processors from scratch can easily dive into it.
I've documented all the development progresses, train of thoughts, debug logs. I assume this would work as a mistake notebook or a guideline for RISC-V beginners, Processor design field.
Since most of lectures I've heard were using Verilog, all of RTL codes we provide are written in pure Verilog.

"A guideline for processor designing from scratch for begginer that has made by an actual beginner."

Key Features

📦 What's in it? : CPU + SoC + framework for learning.
⌨️ Written in pure Verilog 2001.
🧱 Modular design for each core design, enhancing the scalability of the architecture and helping understanding.
🔌 FPGA Synthesizable sources.
📚 Fully documentized for easy hand-on learning for beginners. ( Repository's purpose )
(develop logs, debug traces, train of thoughts, rationales, module logic explainations, signal-level diagrams... etc.)

Quick Start

📕 Tutorials
Architecture Design? How to use this repository? Let's get started.
📊 Diagrams
Processor architecture design block diagrams including the draft files.
📜 Devlogs
Want to find out how did we made this processor? Here's the footprints of it.

Branches & Directories

📌 Branches

main
Latest released version of the repository.
develop
Current ongoing version of the repository.
This branch only revises the RTL source code in modules/ and testbenches/.
docs
Revises the documents/ directory.

📌 Directories

🗂 Documents
- /diagrams
  Processor design's signal-level block diagrams, Including archived legacies.
  PDF, PNG, drawio files.
- /guidelines
  Annotated RTL sources, tutorials: processor design methodologies, organized devlogs, debug logs.
  - /architecture_logics
    Description of each designed architecture down to logic block's signal and logics.
  - /annotated_rtl
    Annotated verilog RTL source code about each module designs for hands-on learning.
- /archives
  archived architecture designs, documents... etc.
- /project_devlog
  The raw development logs of main contributors.
- /references
  References that helped.
💾 Sources
- /modules
  Clean RTL source code of actual synthesized core.
- /testbenches
  Testbench RTL code of each module ( top module, module instances )
  result with .vvp and waveform .vcd files included.
- /fpga
  Vivado project files for FPGA synthesis and implementation.
  Contains such as .xpr .xdc files to import the whole project easily.
  Also, the project file includes clean RTL code without annotations.

About Guidelines

basic_RV32s follows three design principles to guide an intuitive and efficient hardware architecture design.

Streamline I/O signals to reduce complextiy.
Define clear module roles with focused logic to enhance modularity.
Prioritize performance improvements even when conflicting with the above principles, with effectiveness validated through testing.

In directory guidelines/, we provide comprehensive resources for learning and understanding the design of processors in basic_RV32s.

🗃 Incremental architecture documentation
& 📜 Design iteration histories
presenting each evolution with design decisions.
📑 Dual-format verilog RTL source code
offering annotated version from clean source code.
📖 Development logs, Debug traces
organized version based on raw devlogs located in documents/project_devlog/ with problem-solving approaches.
🔬 Verification methodologies providing UART-based debugging and Dhrystone benchmark setup on FPGA.

The Development logs might possibly not match with the current design, if there's some certain missing logs which is needed, you may request for it.
_{Un-organized raw devlog in documents/project_devlog contains more information than the organized logs in guidelines/ but even non-relative words are included. Also, project's developers are from Republic of Korea. All the raw devlogs are written originally in Korean. Please be aware of these.}

In architecture documentations, we've included the specifications of all modules with Signal-level Block Diagram. The I/O signals of each module, the purpose of the modules, logic behavior. This contains not only the top CPU module, but all modules that constructs the processor.

Since the last processor design of basic_RV32s is synthesized and implemented on FPGA, we also provide a project file so everyone can modify and implement the suggested core design.

This project was done in limited environment (serving military duty, only 1 FPGA board, 2 developers, approx. 2 hours per day). We hope some other implementation reports. Please contact us if you have already. 📡

Architectures and Specifications

Naming conventions

RV32I43F = RV32I that supports 43 instructions. Final(latest) version.
RV32I46F_5SP = RV32I that supports 46 instructions. Final(latest) version. 5-Stage Pipelined architecture.

basic_RV32s provides 4 RISC-V core designs and 1 SoC design for FPGA verification.

Processor	ISA	Added modules	note
RV32I37F	RV32I^a	-	Base single-cycle architecture
RV32I43F	RV32I^a +Zicsr	CSR File	supports Zicsr 6 instructions
RV32I46F	RV32I^b +Zicsr	Exception Detector, Trap Controller, MUXs	supports ECALL, EBREAK
RV32I46F_5SP	RV32I^b +Zicsr	2-bit FSM Dynamic Branch Predictor, Hazard Unit, Forward Unit	5-Stage Pipelined
46F5SP_SoC^*	-	Button Controller, Debug UART Controller, UART TX, Benchmark Controller	GPIO, UART implemented SoC for Dhrystone

^a Partial RV32I which excluded ECALL, EBREAK, FENCE, FENCE.TSO, PAUSE instructions.
^b Partial RV32I which excluded FENCE, FENCE.TSO, PAUSE instructions.
^* 46F5SP_SoC is made for debugging and running Dhrystone benchmark the core design.
It utilizes FPGA on-board GPIOs such as LEDs, buttons and UART.

_{Architectures of basic_RV32s' processors}

RV32I37F

ISA: RISC-V RV32I v2.1
(except fence, fence.tso, pause, ecall, ebreak = total 37 instructions)

Total 14 Modules, 74 Signals.

Click to view Modules and Signals table

Module name	Acronyms	Inputs	Outputs	Signals
Program Control
Program Counter	PC	next_pc, clk, reset	pc	3+1=4
PC Controller	PCC	jump, branch_taken, pc, imm, jump_target	next_pc	5+1=6
PC Aligner	-	raw_next_pc	next_pc	1+1=2
Memory Units
Instruction Memory	IM	pc	instruction	1+1=2
Instruction Decoder	ID	instruction	opcode, funct3, funct7, rs1, rs2, rd, raw_imm	1+7=8
Register File	Reg	clk, read_reg1, read_reg2, write_reg, write_data, write_enable	read_data1, read_data2	6+2=8
Data Memory	DM	clk, write_enable, address, write_data, write_mask	read_data	5+1=6
Controls
Control Unit	CU	opcode, funct3	jump, branch, alu_src_A_select, alu_src_B_select, register_file_write, register_file_write_data_select, memory_read, memory_write	2+8=10
ALU Controller	-	opcode, funct3, funct7_5, imm_10	alu_op	4+1=5
Executions
Arithmetic Logic Unit	ALU	srcA, srcB, alu_op	alu_result, alu_zero	3+2=5
Branch Logic	-	branch, alu_zero, funct3	branch_taken	3+1=4
Byte Enable Logic	BE_Logic	memory_read, memory_write, funct3, register_file_read_data, data_memory_read_data, address	register_file_write_data, data_memory_write_data, write_mask	6+3=9
Immediate Generator	imm_gen	opcode, raw_imm	imm	2+1=3
PC plus 4	-	pc	pc_plus_4	1+1=2
MUXs
ALUsrcMUX_A	-	read_data1, pc, alu_src_A_select	srcA
ALUsrcMUX_B	-	read_data2, imm, alu_src_B_select	srcB
Reg_WD_MUX	-	byte_enable_logic_register_write_data, alu_result, imm, pc_plus_4	register_file_write_data

⚠️ Note: Misaligned address access is handled as zeroing the low 2-bits from address.

For each module's logic description, go to documents/modules_and_signals/ for more information. Each module has its own logic behavior documentations which includes I/O signals, Logics and Note.

RV32I43F

ISA: RISC-V RV32I v2.1 + Zicsr v2.0 (except fence, fence.tso, pause, ecall, ebreak = total 43 instructions)

Total 15 Modules, 81 Signals.

Click to view Modules and Signals table

Module name	Acronyms	Inputs	Outputs	Signals
Program Control
Program Counter	PC	next_pc, clk, reset	pc	3+1=4
PC Controller	PCC	jump, branch_taken, pc, imm, jump_target	next_pc	5+1=6
PC Aligner	-	raw_next_pc	next_pc	1+1=2
Memory Units
Instruction Memory	IM	pc	instruction	1+1=2
Instruction Decoder	ID	instruction	opcode, funct3, funct7, rs1, rs2, rd, raw_imm	1+7=8
Register File	Reg	clk, read_reg1, read_reg2, write_reg, write_data, write_enable	read_data1, read_data2	6+2=8
Data Memory	DM	clk, write_enable, address, write_data, write_mask	read_data	5+1=6
CSR File	-	clk, reset, csr_write_enable, csr_address, csr_write_data	csr_read_out	5+1=6
Controls
Control Unit	CU	opcode, funct3	jump, branch, alu_src_A_select, alu_src_B_select, register_file_write, register_file_write_data_select, memory_read, memory_write, csr_write_enable	2+9=11
ALU Controller	-	opcode, funct3, funct7_5, imm_10	alu_op	4+1=5
Executions
Arithmetic Logic Unit	ALU	srcA, srcB, alu_op	alu_result, alu_zero	3+2=5
Branch Logic	-	branch, alu_zero, funct3	branch_taken	3+1=4
Byte Enable Logic	BE_Logic	memory_read, memory_write, funct3, register_file_read_data, data_memory_read_data, address	register_file_write_data, data_memory_write_data, write_mask	6+3=9
Immediate Generator	imm_gen	opcode, raw_imm	imm	2+1=3
PC plus 4	-	pc	pc_plus_4	1+1=2
MUXs
ALUsrcMUX_A	-	read_data1, pc, rs1, alu_src_A_select	srcA
ALUsrcMUX_B	-	read_data2, imm, csr_read_data, alu_src_B_select	srcB
Reg_WD_MUX	-	byte_enable_logic_register_write_data, alu_result, imm, pc_plus_4, csr_read_data	register_file_write_data

Supported CSRs:

CSR	address₁₆	Read-Only	WLRL, WARL
mvendorid	F11	O	-
marchid	F12	O	-
mimpid	F13	O	-
mhartid	F14	O	-
mstatus	300	-	-
misa	301	-	WARL
mtvec	305	-	WARL
mepc	341	-	WARL
mcause	342	-	WLRL

^{WLRL = Write Legal, Read Legal. WARL = Write Any, Read Legal.}

⚠️ Notes

Misaligned address access is handled as zeroing the low 2-bits from address.
In RV32I46F_5SP, the CSR logics are changed. For executing the trap and exceptions during the pipeline, the address signal separated to read address and write address input.
mhartid is a dummy value for read-only CSR design test. No multi-hart architecture is available now.

For each module's logic description, go to documents/modules_and_signals/ for more information. Each module has its own logic behavior documentations which includes I/O signals, Logics and Note.

RV32I46F

ISA: RISC-V RV32I v2.1 + Zicsr v2.0 + mret*
(except fence, fence.tso, pause, = total 46 instructions)
^{*privileged architecture version 20240411, 3.3.2. Trap-Return Instructions, page 51}
Total 16 Modules, 102 Signals.

Click to view Modules and Signals table

Modules and Signals table

Module name	Acronyms	Inputs	Outputs	Signals
Program Control
Program Counter	PC	next_pc, clk, reset	pc	3+1=4
PC Controller	PCC	pcc_op, pc, branch_target, jump_target	next_pc	4+1=5
Exception Detector	ED	clk, reset, opcode, funct3, alu_result, funct12, csr_write_enable, branch_target_lsbs	trapped, trap_status	8+2=10
Trap Controller	TC	clk, reset, pc, trap_status, csr_read_data	trap_target, debug_mode, csr_write_enable, csr_trap_address, csr_trap_write_data, trap_done	5+6=11
Memory Units
Instruction Memory	IM	pc	im_instruction	1+1=2
Instruction Decoder	ID	instruction	opcode, funct3, funct7, rs1, rs2, rd, raw_imm	1+7=8
Register File	Reg	clk, read_reg1, read_reg2, write_reg, write_data, write_enable	read_data1, read_data2	6+2=8
Data Memory	DM	clk, write_enable, address, write_data, write_mask	read_data	5+1=6
CSR File	-	clk, reset, csr_write_enable, csr_address, csr_write_data	csr_read_out	5+1=6
Controls
Control Unit	CU	opcode, funct3, branch_taken, trapped, trap_done	pcc_op, alu_src_A_select, alu_src_B_select, register_file_write, register_file_write_data_select, memory_read, memory_write, csr_write_enable	5+8=13
ALU Controller	-	opcode, funct3, funct7_5, imm_10	alu_op	4+1=5
Executions
Arithmetic Logic Unit	ALU	srcA, srcB, alu_op	alu_result, alu_zero	3+2=5
Branch Logic	-	branch, alu_zero, funct3, pc, imm	branch_taken, branch_target	5+2=7
Byte Enable Logic	BE_Logic	memory_read, memory_write, funct3, register_file_read_data, data_memory_read_data, address	register_file_write_data, data_memory_write_data, write_mask	6+3=9
Immediate Generator	imm_gen	opcode, raw_imm	imm	2+1=3
PC plus 4	-	pc	pc_plus_4	1+1=2
MUXs
ALUsrcMUX_A	-	read_data1, pc, rs1, alu_src_A_select	srcA
ALUsrcMUX_B	-	read_data2, imm, csr_read_data, alu_src_B_select	srcB
Reg_WD_MUX	-	byte_enable_logic_register_write_data, alu_result, imm, pc_plus_4, csr_read_data	register_file_write_data
**CSR_addr_MUX	-	trapped, raw_imm, csr_trap_address	csr_address**
**CSR_addr_MUX	-	trapped, csr_trap_write_data, alu_result	csr_write_data**
**DBG_RD_MUX	-	debug_mode, im_instruction, dbg_instruction	instruction**

⚠️ Notes

Misaligned address access is now handled with Exception Handling
Operations that should be done before branching to the Trap Handler, such as writing mcause, mepc CSRs and reading mtvec is done in Trap Controller module. (Pre-Trap Handling; PTH)
This PTH consumes about 5 Clock cycles.
CSR configurations are same as 43F architecture.

For each module's logic description, go to documents/modules_and_signals/ for more information. Each module has its own logic behavior documentations which includes I/O signals, Logics and Note.

RV32I46F_5SP

ISA: RISC-V RV32I v2.1 + Zicsr v2.0 + mret*
(except fence, fence.tso, pause, = total 46 instructions)
^{*privileged architecture version 20240411, 3.3.2. Trap-Return Instructions, page 51}
Total 23 Modules, 338 Signals.

Click to view Modules and Signals table

Modules and Signals table

Module name	Acronyms	Inputs	Outputs	Signals
Program Control
Program Counter	PC	clk, reset, next_pc	pc	3+1=4
PC Controller	PCC	jump, branch_estimation, branch_prediction_miss, trapped, pc, jump_target, branch_target, branch_target_actual, trap_target, pc_stall	next_pc	10+1=11
Exception Detector	ED	clk, reset, ID_opcode, EX_opcode, MEM_opcode, ID_funct3, EX_funct3, MEM_funct3, alu_result, MEM_alu_result, raw_imm, EX_raw_imm, csr_write_enable, branch_target_lsbs, branch_estimation	trapped, trap_status	15+2=17
Trap Controller	TC	clk, reset, ID_pc, EX_pc, MEM_pc, WB_pc, trap_status, csr_read_data	trap_target, debug_mode, csr_write_enable, csr_trap_address, csr_trap_write_data, trap_done, misaligned_instruction_flush, misaligned_memory_flush, pth_done_flush, standby_mode	8+10=18
Memory Units
Instruction Memory	IM	pc	im_instruction	1+1=2
Instruction Decoder	ID	instruction	opcode, funct3, funct7, rs1, rs2, rd, raw_imm	1+7=8
Register File	Reg	clk, read_reg1, read_reg2, write_reg, write_data, write_enable	read_data1, read_data2	6+2=8
Data Memory	DM	clk, write_enable, address, write_data, write_mask	read_data	5+1=6
CSR File	-	clk, reset, trapped, csr_write_enable, csr_read_address, csr_write_address, csr_write_data	csr_read_out, csr_ready	7+2=9
Controls
Control Unit	CU	opcode, funct3, trap_done, csr_ready	jump, branch, alu_src_A_select, alu_src_B_select, register_file_write, register_file_write_data_select, memory_read, memory_write, csr_write_enable, pc_stall	4+10=14
ALU Controller	-	opcode, funct3, funct7_5, imm_10	alu_op	4+1=5
Executions
Arithmetic Logic Unit	ALU	srcA, srcB, alu_op	alu_result, alu_zero	3+2=5
Branch Logic	-	branch, branch_estimation, alu_zero, funct3, pc, imm	branch_taken, branch_target_actual, branch_prediction_miss	6+3=9
Byte Enable Logic	BE_Logic	memory_read, memory_write, funct3, register_file_read_data, data_memory_read_data, address	register_file_write_data, data_memory_write_data, write_mask	6+3=9
Immediate Generator	imm_gen	opcode, raw_imm	imm	2+1=3
PC plus 4	-	pc	pc_plus_4	1+1=2
Pipelines
IF ID Register	IF/ID	clk, reset, flush, IF_ID_stall, IF_pc, IF_pc_plus_4, IF_instruction, IF_branch_estimation	ID_pc, ID_pc_plus_4, ID_instruction, ID_branch_estimation	9+4=13
ID EX Register	ID/EX	clk, reset, flush, ID_EX_stall, ID_pc, ID_pc_plus_4, ID_branch_estimation, ID_instruction, ID_jump, ID_branch, ID_alu_src_A_select, ID_alu_src_B_select, ID_memory_read, ID_memory_write, ID_register_file_write_data_select, ID_register_write_enable, ID_csr_write_enable, ID_opcode, ID_funct3, ID_funct7, ID_rd, ID_raw_imm, ID_read_data1, ID_read_data2, ID_rs1, ID_rs2, ID_imm, ID_csr_read_data	EX_pc, EX_pc_plus_4, EX_branch_estimation, EX_instruction, EX_jump, EX_memory_read, EX_memory_write, EX_register_file_write_data_select, EX_register_write_enable, EX_branch, EX_alu_src_A_select, EX_alu_src_B_select, EX_opcode, EX_funct3, EX_funct7, EX_rd, EX_raw_imm, EX_read_data1, EX_read_data2, EX_rs1, EX_rs2, EX_imm, EX_csr_read_data	28+24=52
EX MEM Register	EX/MEM	clk, reset, flush, EX_MEM_stall, EX_pc, EX_pc_plus_4, EX_instruction, EX_memory_read, EX_memory_write, EX_register_file_write_data_select, EX_register_write_enable, EX_opcode, EX_funct3, EX_rs1, EX_rd, EX_read_data2, EX_imm, EX_raw_imm, EX_csr_read_data, EX_alu_result	MEM_pc, MEM_pc_plus_4, MEM_instruction, MEM_memory_read, MEM_memory_write, MEM_register_file_write_data_select, MEM_register_write_enable, MEM_csr_write_enable, MEM_opcode, MEM_funct3, MEM_rs1, MEM_rd, MEM_read_data2, MEM_imm, MEM_raw_imm, MEM_csr_read_data, MEM_alu_result	21+17=38
MEM WB Register	MEM/WB	clk, reset, MEM_WB_stall, flush, MEM_pc, MEM_pc_plus_4, MEM_instruction, MEM_register_file_write_data_select, MEM_imm, MEM_raw_imm, MEM_csr_read_data, MEM_alu_result, MEM_register_write_enable, MEM_csr_write_enable, MEM_rs1, MEM_rd, MEM_opcode, MEM_byte_enable_logic_register_file_write_data	WB_pc, WB_pc_plus_4, WB_instruction, WB_register_file_write_data_select, WB_imm, WB_raw_imm, WB_csr_read_data, WB_alu_result, WB_register_write_enable, WB_csr_write_enable, WB_rs1, WB_rd, WB_opcode, WB_byte_enable_logic_register_file_write_data	18+14=32
Hazard Unit	-	clk, reset, trap_done, csr_ready, standby_mode, trap_status, misaligned_instruction_flush, misaligned_memory_flush, pth_done_flush, ID_rs1, ID_rs2, ID_raw_imm, MEM_rd, MEM_register_write_enable, MEM_csr_write_enable, MEM_csr_write_address, WB_rd, WB_register_write_enable, WB_csr_write_enable, WB_csr_write_address, EX_rd, EX_opcode, EX_rs1, EX_rs2, EX_imm, EX_csr_write_enable, EX_jump, branch_prediction_miss	hazard_mem, hazard_wb, csr_hazard_mem, csr_hazard_wb, IF_ID_flush, ID_EX_flush, EX_MEM_flush, MEM_WB_flush, IF_ID_stall, ID_EX_stall, EX_MEM_stall, MEM_WB_stall	28+12=40
Forward Unit	-	hazard_mem, MEM_imm, MEM_alu_result, MEM_csr_read_data, MEM_pc_plus_4, MEM_opcode, byte_enable_logic_register_file_write_data, hazard_wb, WB_imm, WB_alu_result, WB_csr_read_data, WB_byte_enable_logic_register_file_write_data, WB_pc_plus_4, WB_opcode, csr_hazard_mem, csr_hazard_wb, MEM_csr_write_data, WB_csr_write_data, csr_read_data	alu_forward_source_data_a, alu_forward_source_data_b, alu_forward_source_select_a, alu_forward_source_select_b, csr_forward_data	19+5=24
Branch Predictor	BP	**clk, reset, IF_opcode, IF_pc, IF_imm, EX_branch, EX_branch_taken	branch_estimation, branch_target**	7+2=9
MUXs
**ALUsrcMUX_A	-	EX_read_data1, EX_pc, EX_rs1, EX_alu_src_A_select**	srcA
**ALUsrcMUX_B	-	EX_read_data2, EX_imm, EX_csr_read_data, EX_alu_src_B_select**	srcB
**ALUsrc_forward_MUX_A	-	alu_forward_source_select_a, alu_forward_source_data_a, srcA	ALUsrcA**
**ALUsrc_forward_MUX_B	-	alu_forward_source_select_b, alu_forward_source_data_b, srcB	ALUsrcB**
Reg_WD_MUX	-	**WB_byte_enable_logic_register_write_data, WB_alu_result, WB_imm, WB_pc_plus_4, WB_csr_read_data	WB_register_file_write_data**
CSR_read_addr_MUX	-	**trapped, standby_mode, raw_imm, csr_trap_address	csr_read_address**
CSR_write_addr_MUX	-	**trapped, standby_mode, WB_raw_imm, csr_trap_address	csr_write_address**
CSR_data_MUX	-	trapped, standby_mode, csr_trap_write_data, WB_alu_result	csr_write_data
DBG_RD_MUX	-	debug_mode, im_instruction, dbg_instruction	instruction

⚠️ Notes

46F_5SP architecture was designed to be implemented on FPGA. So some modules have turned to Syncrhonous modules.
This made some hazards. Please be aware of these which is written in issues.
Since the Exception Detector logic and CSR File have been changed to Synchronous, PTH now consumes about 10 Clock cycles.
CSR configurations are same as 43F architecture.
To run C program, the bypass logic between Instruction Memory and Data Memory is required (since the toolchain linker divides the ROM and RAM address map.). Please check the core design in fpga/ for running C program on our SoC.

For each module's logic description, go to documents/modules_and_signals/ for more information. Each module has its own logic behavior documentations which includes I/O signals, Logics and Note.

FPGA Implementation Results

RV32I46F_5SP core implemented 46F5SP_SoC was implemented on Digilent Nexys Video board (AMD Xilinx Artix-7 XC7A200T FPGA).
FPGA Synthesis and Implementations were done in Vivado 2024.2.

20ns (50 MHz) timing constraints
Synthesis Strategy : Flow_PerfOptimized_high
Implementation Strategy : Performance_Explore

Single-Cycle processors' FPGA implementation is not done yet. It will be added soon after the military duty ends. (Around Sep. 2025)
Table below is FPGA implementation results.

Processor	LUTs	FFs	BRAMs	DSPs	Fmax	DMIPS/MHz
46F5SP_SoC	11,660^*	2,383	0^**	0	50 MHz	1.09
RV32I46F_5SP	3,010	2,383	0^**	0	``	``
RV32I46F	-	-	-	-	-	-
RV32I43F	-	-	-	-	-	-
RV32I37F	-	-	-	-	-	-

^{* Dhrystone benchmark and Trap Handler hard coded using readmemh. Resource varies depends on the program in memories. This will soon be standardized.}
^{** All memories are inferred as LUT-based distributed RAM.}

Various performance benchmark (such as coremark) will be added soon.
We assume that the processor can reach higher clock speed and performance, but at the moment we couldn't continue development in touch due to personal schedule (military duty, school admission).
This will be worked soon also.

Getting Started

basic_RV32s can be simply cloned by using

$ git clone https://github.com/RISC-KC/basic_rv32s.git

🔎 Core behavior Simulations

Required : Icarus Verilog for using ./test.sh command.

$ cd [source_code_directory]
$ ./test.sh RV32I37F.v RV32I37F_tb.v

This would run testbench as coded in testbenches/.
The result of the simulation .vvp is generated in testbenches/results/.
.vcd waveform result is generated in testbenches/results/waveforms/.

Waveform can be viewed using GTKwave or Surfer-project.

🎛 FPGA implementation

Vivado environment (tested on 2024.2)
- In fpga/ directory, select architecture source directory which you want to implement on your FPGA. (37F, 43F, 46F, 46F_5SP)
  Launch Vivado and import project file which you have selected.
- Current FPGA implementation's SoC can be applied to 43F, 46F, 46F5SP architecture. (release v1.0.0)
  37F Architecture needs additional logics to replace the existing mcycle and minstret CSR to implement on 46F5SP_SoC since it doesn't have CSR module.
- The RTL source code of RV32I46F_5SP in fpga/ directory has clk_enable signal for sequential execution debugging.
  If you need only the core IP itself, use the source in modules/ directory.
Other IDE
You can manually import the sources located in modules/ directory.

📥 Setup RV32I RISC-V GNU toolchain with GCC.

Follow this guideline provided by official RISC-V github. https://github.com/riscv-collab/riscv-gnu-toolchain

Make sure to configure the toolchain build with one of the following commands.

./configure --with-multilib-generator="rv32i-ilp32--"
or
./configure --prefix=/opt/riscv --with-arch=rv32i --with-abi=ilp32
make linux

⚠️ Notice

Default program is some RV32I instructions which is integrated in Insturction Memory.
If you are going to simulate the C program which has been compiled through RISC-V GNU GCC toolchain; RV32I, the memory configuration is needed.
Make sure the linker script of the compile's memory map is same as following.

...
MEMORY
{
    ROM (rx) : ORIGIN = 0x00000000, LENGTH = 64K
    RAM (rw) : ORIGIN = 0x10000000, LENGTH = 32K
}
...

If you are not a beginner like I was, you can just modify this memory settings.
Since the actual FPGA implementation is only done in RV32I46F_5SP, we suggest to use 46F_5SP architecture for C compiled program simulation.

We're going to work on easy C program import on SoC soon.

Future Works

issue resolutions
Single-Cycle core FPGA implementation and Evaluation
Additional benchmarks (Coremark, RISC-V ISA tests)
Standardized FPGA synthesis resource measurement
Optimize critical paths and reach higher clock speed and performance
Easy method for running C program on SoC

Contributions

This repository is not Frozen or Completed ❄️!

Most of repository structure has been designed, but still some documents are on-going.
Since the project is being done in limited environment (military duty), this could take some time.
We are currently targeting October 2025 to complete the entire documentation plan as described in the README.

Since it's still an open-source RISC-V core implementation and instructional framework, the changes can be done as needed.
Please feel free to generate an issue for improving this project to make it possible to newcommers and beginners can easily dive in to RISC-V and Processor Design.

Thanks! 📡

Acknowledgment

Heartfelt thanks to @ChoiCube84 for being an incredible project companion throughout this processor design journey. Even in the challenging environment of military service, your consistent support and dedication made this project possible.

Contributors:

@T410N (KHWL) - Project Lead & Architecture Design
@ChoiCube84 - Development & Project support

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references		references
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🎛 FPGA implementation

📥 Setup RV32I RISC-V GNU toolchain with GCC.

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