LeveretOS_

Try the latest build

Boot the latest version of LeveretOS in browser! No install required. This runs the same ISO as the latest lesson.

The idea

Each lesson will have its own folder, and will add one new feature on top of the last. New or changed code will contain comments to guide you through each step. Note that reused code will be left without educative comments to improve simplicity.

How to follow each lesson

Each lesson folder is a copy of the one before, with the addition of one new feature. It is unnecessary to reread every file each lesson. A few files change per lesson, and you can see them in the following ways:

• Every lesson folder has a .LessonOverview.txt, which explains what the lesson adds and lists which files were added or changed.
• Inside those files, the new or changed code is marked with educational comments. Search a file for "new" to see new code. Note that minor changes may not be marked. Reused code from earlier lessons is usually left without educational comments, allowing the new code to be easily visible.
• To see all changes at the same time, you can compare the lesson folder with the previous one. With git, run git diff --no-index 12-Shell/src 13-Timer/src (swap in the two folders). New lines are shown in green and removed lines in red. You can also browse the code on GitHub.

When studying lessons, the recommended way is: read the overview, open the changed files, look for the new-code comments, and compare the differences with git diff.

Why "LeveretOS"?

A leveret is a baby hare, small, quick, and one of the fastest-growing young animals around. It felt like the right mascot for an OS that started as almost nothing and will grow a little better with every lesson.

Photo by Tony Stoddard on Unsplash.

Lessons so far

Fundamentals

Talking to the Hardware

Managing Memory

Getting Online

Building and running a lesson

Don't want to download anything? Every lesson can be booted in browser, just press the "Boot" button on any lesson above. If you'd rather build it yourself, you can use the following methods.

Each lesson folder is self-contained and includes a build.sh that assembles the bootloader, compiles the kernel, makes a bootable ISO, and launches it in QEMU. You will need nasm, a 32-bit-capable g++, grub-mkrescue, xorriso, and qemu-system-i386 (on Windows, a Linux environment such as WSL works well).

A good guide for setting up the necessary software to be able to boot: OSDev Bare Bones.

Building with Docker (macOS, Windows, or Linux)

If you don't want to install everything by hand, the repo includes a Dockerfile with the build environment. You only need Docker to build, and QEMU to run.

# From the repo root, build the toolchain container once:
docker build -t leveretos .

# Build a lesson's ISO inside the container (change the folder for other lessons):
docker run --platform linux/amd64 --rm -v "$PWD":/src -w /src/06-Scrolling leveretos ../build-iso.sh

# Run the resulting ISO with QEMU on your own machine:
qemu-system-i386 -cdrom 06-Scrolling/build/LeveretOS-Scrolling.iso

The container is pinned to x86-64, so on Apple Silicon Macs Docker can emulate it (a little slower, but it works). The ISO is written to the lesson's build/ folder, so you run it with QEMU on the host.

Goals

The first big goal is a LeveretOS that can go online and open a web page. These are the checkpoints we have set to reach our goal.

• ✓Play a game (Rock Paper Scissors)
• ✓Type commands into terminal
• ✓Create a running clock
• ✓Login screen at startup
• ✓Graphics processing, so our browser gets a 2D display.
• ✓Open a page from the web

Once we can browse the web, our goals can get bigger. This is where LeveretOS will grow from a single program into something closer to a real operating system.

• ✓Log in securely, with a real password
• ✓Create, open, and manage files
• ✓Write and save notes in a text editor
• ✓Run separate apps, instead of everything being one program
• ✓Open the web browser as one of those apps