Assignment3: Single-cycle RISC-V CPU

contributed by < terry23304 >

Hello World in Chisel

class Hello extends Module {
  val io = IO(new Bundle {
    val led = Output(UInt(1.W))
  })
  val CNT_MAX = (50000000 / 2 - 1).U;
  val cntReg  = RegInit(0.U(32.W))
  val blkReg  = RegInit(0.U(1.W))
  cntReg := cntReg + 1.U
  when(cntReg === CNT_MAX) {
    cntReg := 0.U
    blkReg := ~blkReg                                                         
  }
  io.led := blkReg
}

Switch the LED output every CNT_MAX clock cycles.
It is a I/O Bundle that has only one output signal and no input signals. It includes two registers, cntReg and blkReg, cntReg is used to count the number of clock cycles passed. When it reachesCNT_MAX, which is 24999999, reset cntReg to 0 and invert the value of blkReg. The output will be the same as blkReg

MyCPU

Instruction Fetch

Using jump_flag_id to determine next pc will be jump_address_id or pc + 4.

instruction valid is false only in the beginning. Therefore, the instruction is 0x00000013, and after that, the instruction will be 0x00000000.

Instruction Decode

The testing instruction would be:

• sw x10, 4(x0)
• lui x5, 2
• add x3, x1, x2

Set memory_read_enable to 1 when the instruction is of L type and set memory_write_enable to 1 when the instruction is of S type. Therefore, memory_write_enable is set to 1 only when executing the instruction sw x10, 4(x0).

Execute

Using aluop_source to determine the values of op1 and op2. When aluop_source is 0, op will be set to the data in register; otherwise, op will be set to 0 and immediate value.

Run RISC-V assembly code in Homework2

• Move assembly code to csrc directory.
• Modify the makefile in csrc directory to generate corresponding .asmbin file
  ​​​​BINS = \
  ​fibonacci.asmbin \
  ​hello.asmbin \
  ​mmio.asmbin \
  ​quicksort.asmbin \
  ​sb.asmbin \
  ​binarization.asmbin
  

• Add test in CPUTest.scala
• Run make update
• Run sbt "testOnly riscv.singlecycle.BinarizationTest"

[info] BinarizationTest:
[info] Single Cycle CPU
[info] - should do binarization with threshold 128
[info] Run completed in 3 seconds, 314 milliseconds.
[info] Total number of tests run: 1
[info] Suites: completed 1, aborted 0
[info] Tests: succeeded 1, failed 0, canceled 0, ignored 0, pending 0
[info] All tests passed.
[success] Total time: 4 s, completed Dec 1, 2023, 12:24:30 AM

Analysis

Execute the following command to generate Verilog file.z

$ make verilator
$ ./run-verilator.sh -instruction src/main/resources/binarization.asmbin -time 2000 -vcd dump.vcd

Then, run gtkwave dump.vcd to check waveform.