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Super simple microcodedd RISCV32I cpu.

  • 3(LUI/AUIPC/JAL), 4(ALU/BRANCH/JALR), 6(STORE/LOAD) clocks cycles per instrution.
  • No fence or CSR instructions (emulated with system rom)
  • No MMU.
  • Uses APB bus.
  • Runs Linux
  • Uses Verilator

To try out yourself

  • Download and compile the latest Verilator
  • Download and compile the lastest Binutils and gcc
git submodule update --init --recursive
./dl_toolchain.sh
make CROSS_COMPILE=riscv32-unknown-elf- run_tests
make CROSS_COMPILE=riscv32-unknown-elf- testkern

TODOS

  • Get running of actual FPGA

Notes

Tested on

  • GNU Binutils: 2.40.0.20230214
  • riscv32-unknown-elf-gcc (g2ee5e430018) 12.2.0
  • Verilator v5.012

Used precompiled:

https://github.com/riscv-collab/riscv-gnu-toolchain/releases/tag/2023.06.09

riscv32-elf-ubuntu-22.04-nightly-2023.06.09-nightly.tar.gz

Verilator has a few bugs in older verisons so you can't run make VFLAGS='--assert'

Older version of binutils:

objcopy doesnt work when using --verilog-data-width=4 --reverse-bytes=4 when converting from elf to verilog mem files.

To get around this we first copy to raw binary then use the folowing to convert to verilog memfile. objcopy -Ibinary -O verilog --verilog-data-width=4 --reverse-bytes=4 test.bin test.mem