Sophon

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

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

Kernel

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

User Space

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

Architectures

• AArch64
• X86_64
• X86
• ARMv6-M (RTOS)

Others

• Unit / integration tests
• 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