Sophon - A Raspberry Pi Kernel in Rust

An experimental modular-kernel written in Rust.

The name "Sophon" comes from the novel The Three-Body Problem.

Getting Started

Preparation

1. Install rustup.
2. qemu-system-aarch64 (optionally gdb-multiarch or lldb for debugging).
3. For debugging: LLVM tools (lldb, llvm-objcopy and llvm-objdump)
4. VSCode setup: install the rust-analyzer extension.

Run on QEMU

$ cargo dev run

Run on a Raspberry Pi 4B

Prepare UEFI and bootable USB (once)

1. Prepare a USB drive with UEFI firmware.
2. Plug the usb to your Raspberry Pi and connect to a HDMI monitor (or using UART0).
3. Start Raspberry Pi and goto UEFI settings menu.
4. Navigate to Device Manager → Raspberry Pi Configuration → Advanced Settings and enable ACPI + Device tree

Install kernel

1. cd boot/uefi
2. make deploy boot=/path/to/your/usb/directory
3. Plug the usb to your Raspberry Pi and connect a serial cable to UART0 ports properly.
4. Use screen to connect to the serial device
   • e.g. screen /dev/tty.usbserial 115200.
5. Start Raspberry Pi

Design

The current plan is:

Make the kernel as simple and small as possible. Instead of following the micro-kernel approach that puts each kernel component as a isolated user process, Sophon tries to treat the components as kernel modules. This is expected to have higher performance than micro-kernels due to the absence of context switches and message passing overheads.

TODO

Boot

• [x] Make the kernel boot on AArch64 QEMU (UEFI)
• [x] Make the kernel boot on a real Raspberry Pi 4B (UEFI)
• [x] Setup EL1 virtual memory
• [x] Load kernel as relocatable ELF
• [x] Start kernel at Exception Level 1
• [ ] UEFI Network boot
• [ ] U-boot support

Kernel

• [x] Initialize drivers based on a device tree
• [x] Basic interrupt handler support
• [x] Kernel heap allocation
• [x] Timer interrupts
• [x] Scheduling / Context switch
• [x] Syscalls support
• [x] Log syscall (output to UART, for user process debugging)
• [x] Kernel Modules
• [x] Module-defined syscalls (Module calls)
• [x] VFS module and Root-FS
• [ ] Memory management module; mmap and munmap syscalls
• [ ] File system modules like fat32
• [x] Process management module
• [x] Process and multi-threading
• [x] Driver interface based on modules
• [ ] SMP support

User Space

• [ ] Properly trap and handle Stack-overflow exception
• [x] Launch init process in privileged mode
• [x] Launch init process in user mode
• [x] TTY
• [ ] Update/release ref-counted pages after process exit
• [ ] Port gcc/libc/rustc

Architectures

• [x] AArch64
• [ ] X86_64
• [ ] X86
• [ ] ARMv6-M (RTOS)

Others

• [x] Unit / integration tests
• [x] Continuous integration (based on GitHub Actions)

References

1. Raspberry Pi Bare Bones Rust - OSDev
2. Mailbox Property Interface
3. Bare Metal Raspberry Pi 3 Tutorials
4. Bare Metal Raspberry Pi 3 Tutorials (Rust)
5. Raspberry Pi Hardware Documents
6. Learning OS dev using Linux kernel & Raspberry Pi
7. ARM Quad-A7 Documentation (for timer configuration)
8. Circle - A C++ bare metal programming env for RPi
9. PanicOS - A simple x86 operating system with graphical user space