s7e11ar / p1-kernel

A tiny, modern kernel on real hardware

A tiny, modern kernel for Raspberry Pi 3

What is it:

A tiny kernel incrementally built for OS education.

We wills start with a minimal, baremetal code piece. Then we will add a set of kernel features in small doses through a series of experiments.

Each experiment is a self-contained and can run on both Rpi3 hardware and QEMU.

Rationale

The kernel must run on cheap & modern hardware.

Showing the kernel's evolution path is important. Along the path, each version must be self-contained runnable.

We deem the following kernel functions crucial to implement:

• protection modes
• interrupt handling
• preemptive scheduling
• virtual memory

Experimenting with these features is difficult with commodity kernels due to their complexity.

Goals

Primary:

• Learning by doing: the core concepts of a modern OS kernel
• Experiencing OS engineering: hands-on programming & debugging at the hardware/software boundary
• Daring to plumb: working with baremetal hardware: CPU protection modes, registers, IO, MMU, etc.

Secondary:

• Armv8 programming. Arm is everywhere, including future Mac.
• Working with C and assembly
• Cross-platform development

Non-goals:

• Non-core or advanced functions of OS kernel, e.g. filesystem or power management, which can be learnt via experimenting with commodity OS.
• Rpi3-specific hardware details. The SoC of Rpi3 is notoriously unfriendly to kernel hackers.
• Implementation details of commodity kernels, e.g. Linux or Windows.

Credits

Derived from the RPi OS project and its tutorials, which is modeled after the Linux kernel.

Key docs

Board manual: Rpi3 board pinout

SoC manual: Bcm

ARM64:

Experiments

0. Sharpen your tools!
1. Helloworld from baremetal
   • Power on + UART bring up
   • Simplifying dev workflow
2. Exception elevated
   • CPU initialization, exception levels
3. Heartbeats on
   • Interrupt handling
4. Process scheduler
   • A. Cooperative
   • B. Preemptive
5. A world of two lands
   • User processes and system calls
6. Into virtual
   • Virtual memory management