pipeRV32N

A simple pipelined 32-bit RISCV core with only 8 base integer registers

Features

• 4-stage RISC-V32 cpu core:
  • IF stage -- instruction fetching
  • ID stage -- instruction decoder
  • EX stage -- execution
  • MEM/WB -- memory and write back
• Contain only 8 basic core registers
• Support for nearly entire base integer instructions for RISC-V32, except synch, environment and CSR instructions
• No pipeline stalling in JAL instruction
• Maximum 2 pipeline stalling when dealing with JALR，Branch instructions
• Utilize a dual port SRAM as main memory to avoid structural hazard
• IF and MEM/WB stages could make pipeline stalling to wait for data reading/writing to memory, compatible for any kind of memory interface.

Further Improvement

• Support for interruptions
• Add control statue registers and support for synch, environment and CSR instructions
• Change the dual port SRAM as CPU cache for both instruction and data
• Support for AXI Bus

Getting Start with pipeRV32N

Platform

• win7 or later version

Software Requirements

• Quartus II
• ModelSim
• Python3
• RISC-V Embedded GCC

Compile your own RISC-V assembly program

• Write a RISC-V assembly program, example like ‘main.s’
  • place this assembly program file under 'test' folder
  • Since the maximum size of main memory for pipeRV32N core is 256 Byte, only small assembly program is allowed
  • Please make sure the entry point is labled as 'main'

.text
.globl main
main:
	la ra, array
	li sp, 10
loop:
	lw t0, 0(ra)
	lw t1, 4(ra)
	lw t2, 8(ra)
	add gp, t0, t1
	add gp, gp, t2
	sw gp, 12(ra)
	addi ra, ra, 4
	addi sp, sp, -1
	bgtz sp, loop
L2:
	j	L2
.data
array: .word 1,1,1
tmp:   .word 0,0,0,0,0,0,0,0,0,0 

• Open a terminal under 'test' folder and compile the RISC-V assembly program:

riscv-none-embed-gcc.exe -c main.s --specs=nosys.specs -march=rv32i -o main.o

• Link:

riscv-none-embed-ld.exe main.o -T .\linker_script.ld  -o main.elf

• Convert it into hex file 'ram.hex':

python .\elf2hex.py main.elf 

• Copy this 'ram.hex' file to replace the one under 'src' folder

Use Quartus to compile and simulate pipeRV32N core

• Create a new Quartus project, choose device family 'Cyclone II' and set ModelSim as simulation tool
• Import these files under ‘src’ folder to project:

core.v
if_stage.v
id_stage.v
ex_stage.v
wb_mem_stage.v
register_file.v
main_memory.v
ram_element.qip

• Set ‘core.v’ as top level entity
• Set ‘test/core_vlg_tst.vt’ as test bench file
• Compile and start simulation

Simulation result example