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RISC-V CPU

Single-Cycle Processor for RISC-V ISA Built in Verilog

SUSTech 2024 Spring's Project of Course CS202 - Computer Organization Led By Professor Jin ZHANG

risc-v cpu

[Read the detailed project requirements]

[Read the detailed project report]

Project Directory

RISC-V CPU
├── assembly_test-risc_v
│   ├── scenario1.asm                                  # assembly code for testing scenario 1
│   ├── scenario1_hex.coe                              # assembly code for testing scenario 1 in hex
│   ├── scenario2.asm                                  # assembly code for testing scenario 2
│   └── scenario2_hex.coe                              # assembly code for testing scenario 2 in hex                              
├── cpu-verilog
│   └── Final_CPU
│       ├── Final_CPU.cache
│       ├── Final_CPU.hw
│       ├── Final_CPU.ip_user_files
│       ├── Final_CPU.runs
│       ├── Final_CPU.sim
│       ├── Final_CPU.srcs
│       │   ├── constrs_1
│       │   │   └── new
│       │   │       └── const.xdc                      # constraint file
│       │   ├── sim_1
│       │   └── sources_1
│       │       ├── ip
│       │       │   ├── RAM
│       │       │   │   ├── dmem32word.coe             # word-addressable data mem
│       │       │   ├── cpu_clk
│       │       │   │   ├── cpu_clk.v
│       │       │   └── prgrom
│       │       │       ├── scenario1.coe              # inst mem for testing scenario 1
│       │       │       ├── scenario2.coe              # inst mem for testing scenario 2
│       │       └── new                                # cpu implementation code
│       │           ├── ALU.v
│       │           ├── CPU.v
│       │           ├── Clock.v
│       │           ├── Controller.v
│       │           ├── DataMem.v
│       │           ├── Decoder.v
│       │           ├── IFetch.v
│       │           ├── IOReader.v
│       │           ├── Led.v
│       │           ├── MemOrIO.v
│       │           ├── Switch.v
│       │           ├── Tube.v
│       │           └── clock_divider.v
│       ├── Final_CPU.xpr                              # main vivado project file
├── project_info
└── README.md

Note: This is a simplified project directory tree. The detailed directory tree can be found here.

CPU Architecture Design

Basic CPU Info

  • Clock Frequency 23Mhz
  • CPI 1
  • Structure Havard Architecture
  • Addressing Unit
    • Registers Support 32 bits for data read and write
    • I/O Support 8 bits or 16 bits for data read, and 8 bits or 32 bits for data write
  • Size of Instruction Space and Data Space 64 KB (2^14 * 4 bytes)
  • Base Address of Stack Space 0x7fffeffc
  • Registers Info 32 registers with each has a bit width of 32 bits

CPU Datapath

risc-v cpu

Supported RISC-V Instructions

R-type

Instruction Encoding Usage Method
ADD 7'b0110011 + funct3:000 + funct7:0000000 add rd, rs1, rs2
SUB 7'b0110011 + funct3:000 + funct7:0100000 sub rd, rs1, rs2
AND 7'b0110011 + funct3:111 + funct7:0000000 and rd, rs1, rs2
OR 7'b0110011 + funct3:110 + funct7:0000000 or rd, rs1, rs2
SLL 7'b0110011 + funct3:001 + funct7:0000000 sll rd, rs1, rs2
SRA 7'b0110011 + funct3:101 + funct7:0100000 sra rd, rs1, rs2

I-type

Instruction Encoding Usage Method
ADDI 7'b0010011 + funct3:000 addi rd, rs1, imm
ANDI 7'b0010011 + funct3:111 andi rd, rs1, imm
ORI 7'b0010011 + funct3:110 ori rd, rs1, imm
XORI 7'b0010011 + funct3:100 xori rd, rs1, imm
SRLI 7'b0010011 + funct3:101 + funct7:0000000 srli rd, rs1, imm
LW 7'b0000011 + funct3:010 lw rd, offset(rs1)
LB 7'b0000011 + funct3:000 lb rd, offset(rs1)
LBU 7'b0000011 + funct3:100 lbu rd, offset(rs1)

S-type

Instruction Encoding Usage Method
SW 7'b0100011 + funct3:010 sw rs2, offset(rs1)

B-type

Instruction Encoding Usage Method
BEQ 7'b1100011 + funct3:000 beq rs1, rs2, offset
BNE 7'b1100011 + funct3:001 bne rs1, rs2, offset
BLT 7'b1100011 + funct3:100 blt rs1, rs2, offset
BGE 7'b1100011 + funct3:101 bge rs1, rs2, offset
BLTU 7'b1100011 + funct3:110 bltu rs1, rs2, offset
BGEU 7'b1100011 + funct3:111 bgeu rs1, rs2, offset

J-type

Instruction Encoding Usage Method
JAL 7'b1101111 jal rd, offset

U-type

Instruction Encoding Usage Method
LUI 7'b0110111 lui rd, imm

FPGA I/O

I/O Support

  • Board: Xilinx Artix-7 FPGA development board, EGO1 (XC7A35T-1CSG324C)
  • Use lw/lb/lbu with negative address to get input
  • Use sw with negative address to display output
  • Address to I/O mapping:
    • 0xfffffc00 16 switches
    • 0xfffffc10 left 8 switches
    • 0xfffffc20 button V1
    • 0xfffffc22 button R11
    • 0xfffffc24 button R17
    • 0xfffffc26 button U4
    • 0xfffffc40 16 LED
    • 0xfffffc60 right 8 LED
    • 0xfffffc69 tube 32-bit
    • 0xfffffc70 tube 16-bit

Control Diagram

risc-v cpu

Note: The top button where it says Confirm Input B in the control diagram should be changed to Confirm Input A.

CPU Testing

To check if the CPU can execute RISC-V instructions correctly, detailed testing schemes are provided here.

Scenario 1: Basic

Test Case Number Test Case Description Passed
3'b000 Input test number a, input test number b, and display the 8-bit binary format of a and b on the output device (LED) ✔️
3'b001 Input test number a, place it in a register by instruction lb, display the value of the 32-bit register in hexadecimal format on the output device (7 segment tubes or VGA), and save the number to memory (in the 3'b011-3'b111 test case, the value of a will be read from the memory unit using the lw instruction for comparison) ✔️
3'b010 Input test number b, place it in a register by instruction lbu, display the value of the 32-bit register in hexadecimal format on the output device (7 segment tubes or VGA), and save the number to memory (in the 3'b011-3'b111 test case, the value of b will be read from the memory unit using the lw instruction for comparison) ✔️
3'b011 Compare test number a and test number b (from test case 3’b001 and test case 3’b010) using instruction beq. If the relationship is true, light up the LED, but if the relationship is not true, turn off the LED ✔️
3'b100 Compare test number a and test number b (from test case 3’b001 and test case 3’b010) using instruction blt. If the relationship is true, light up the LED, but if the relationship is not true, turn off the LED ✔️
3'b101 Compare test number a and test number b (from test case 3’b001 and test case 3’b010) using instruction bge. If the relationship is true, light up the LED, but if the relationship is not true, turn off the LED ✔️
3'b110 Compare test number a and test number b (from test case 3’b001 and test case 3’b010) using instruction bltu. If the relationship is true, light up the LED, but if the relationship is not true, turn off the LED ✔️
3'b111 Compare test number a and test number b (from test case 3’b001 and test case 3’b010) using instruction bgeu. If the relationship is true, light up the LED, but if the relationship is not true, turn off the LED ✔️

Scenario 2: Relatively Complex

Test Case Number Test Case Description Passed
3'b000 Input an 8-bit number, calculate and output the number of leading zeros (the number of leading zeros of 8’b00010000 is 3) ✔️
3'b001 Input a 16-bit IEEE754 encoded half word floating-point number, round it up, and output the rounded result ✔️
3'b010 Input a 16-bit IEEE754 encoded half word floating-point number, round it down, and output the rounded result ✔️
3'b011 Input a 16-bit IEEE754 encoded half word floating-point number, round it, and output the rounded result ✔️
3'b100 Input numbers a and b (each of them is 8-bit) , perform addition operations on a and b. If the sum exceeds 8 bits, remove the high bits and add them up to the sum, then invert the sum, output the result ✔️
3'b101 Input 12-bit or 16-bit data in little endian mode from the dial switch and present it on the output device in big endian mode ✔️
3'b110 Calculate the n-th number of Fibonacci sequence in a recursive manner, record the number of times the stack is pushed and popped, and display the sum of the pushed and popped times on the output device ✔️
3'b111 Calculate the n-th number of Fibonacci sequence in a recursive manner, record the pushed and popped data, display the pushed data on the output device, each pushed data display for 2-3 seconds (note that here we do not focus on the pushed and popped of the value of ra register, hence should output the Fibonacci sequence itself) ✔️

Getting Started

Setup

  • Clone this GitHub repository or download the source code in ZIP then unzip Final_CPU folder at ./cpu-verilog/Final_CPU
  • Have Vivado ready, locate and open .xpr file at ./cpu-verilog/Final_CPU/Final_CPU.xpr
  • Generate bitstream
  • Get the correct FPGA ready, open target, and program the board

Control Manual

  • After programming the board with the .coe file of either scenario 1 or 2, all the 16 LED should be lit up to indicate the initial state of the program
  • Press button S0 to turn off the LED
  • Dial the top 8 switches to select a test case
  • Confirm the the test case with button S3
  • Give the test case an input with either 8 or 16 switches (depend on the test case), confirm the first input with button S4, and confirm the second input with button S1 if there is one
  • Then the CPU shall execute the instructions and output the results either to the LED or 7-segment tube
  • Press button S0 to exit the the test case before choosing another one

Contribution

Contributor CPU Design & Implementation Assembly Code (RISC-V) Report
Jaouhara ZERHOUNI KHAL ✔️ ✔️ ✔️
Layheng HOK ✔️ ✔️ ✔️
Harrold TOK Kwan Hang ✔️ ✔️ ✔️

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CS202 Project: Programming a RISC-V CPU in VHDL

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markdown cpu vhdl vivado instruction-set-architecture risc-v computer-organization

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