SEMU

A simple RISC-V 32 emulator for fun and practice, inspired by NEMU.
This project is the final project for CPL2024.

Installation

1. Set up the environment

Install necessary packages from your distro's package manager:

sudo apt update
sudo apt install build-essential man gdb git libreadline-dev -y

Install SDL3: https://wiki.libsdl.org/SDL3/Installation

2. Build SEMU

Clone the repository and set up the environment:

git clone <repository-url>
cd semu
. scripts/envsetup.sh

Generate .config:

make perf_defconfig

or

make menuconfig

Build:

make

3. Run SEMU

Once the build is complete, you can run the emulator:

make run

To load a program, you can download prebuilt ones from https://github.com/snnbyyds/semu-examples

make run IMG=/path/fceux-mario.bin

Feature Overview

SEMU Infrastructure

kbuild system (tools/kconfig, synced from NEMU)

debuggers (src/monitor)

• sdb (builtin simple debugger with some simple commands)
• gdbstub (an implementation of the GDB Remote Serial Protocol to help debug programs with GDB)

snapshot utility (src/utils)

• snapshot backup & restore

trace (src/utils)

• exception / interruption trace
• instruction trace (Powered by capstone 6)
• function trace (NOT implemented)

expression calculation

• expression calculator (NOT implemented)

difftest

• difftest with NEMU (DUT: SEMU, REF: https://github.com/ics-ext/nemu-ref, not supporting RV32AFD yet)
• difftest with Spike
• serve as a REF for difftest (NOT implemented)

CPU Simulation src/cpu

• Common RV32IMAFD instructions (src/cpu/inst.c)
• GPRs
• CSRs (Basic ones)
• FPRs
• Fetch, decode, execute cycle (src/cpu/cpu.c)
• Basic privileged ISA

( TODO: Make it running even FASTER )

Memory Simulation src/memory

• Basic read and write operations
• RV32 Sv32 paging (Basic)
• TLB (Quite a bad implementation so not enabled by default)
• MMIO src/device/mmio

Device Simulation src/device

• audio (src/device/audio.c)
• disk (src/device/disk.c)
• keyboard (src/device/keyboard.c)
• serial (src/device/serial.c, Input not implemented)
• timer (src/device/timer.c)
• vga (src/device/vga.c)

JIT Mode (WIP)

About HALs and programs

I haven’t had the chance to develop our own Hardware Abstraction Layer, the SAL yet, so for now, I’ve only ported the abstract-machine as the abstraction layer. However, since the code in abstract-machine, nanos-lite, and navy-apps is related to the ICS2024 Programming Assignment, it cannot be made public. Therefore, they will only be distributed in the form of precompiled binaries.

Refs

Inspired by

1. https://github.com/OpenXiangShan/NEMU
2. https://github.com/NJU-ProjectN/nemu
3. https://github.com/sysprog21/rv32emu
4. https://github.com/riscv-software-src/riscv-isa-sim
5. https://github.com/ksco/rvemu
6. https://github.com/snnbyyds/NJU-ICS

Contributing

Feel free to fork the repository and submit a pull request if you’d like to contribute. Bug fixes, performance improvements, and new features are always welcome! Please ensure your contributions follow the coding standards and include appropriate tests.