barebios

A minimal, readable BIOS. Small enough for one person to read end to end.

Status: early days, work in progress. It boots and answers on serial. It is not a usable BIOS yet. Most of the roadmap is still unchecked. tasks.md has the full, current list.

What works today

• Boot sector loads at 0000:7C00, prints to VGA and COM1 (38400 8N1)
• Stage 2 loader reads itself off disk via int 13h, past the 512-byte wall
• Serial command prompt: help, version, echo, dump <hexaddr>, clear, reboot

Build and run

Requires nasm and qemu-system-i386 (or qemu-system-x86_64, set QEMU=).

make            # builds build/barebios.img
make run        # boots it in QEMU with a display
make run-serial # headless, serial in this terminal

With run-serial you get a barebios> prompt. It understands CR as Enter, like a real serial terminal. Scripts should send \r, not \n.

Layout

src/boot.asm    the boot sector, loaded at 0000:7C00, ends in 0xAA55
src/stage2.asm  loaded past the 512-byte wall, hosts the REPL
src/serial.inc  COM1 helpers
tasks.md        the roadmap ledger
Makefile        build + run targets
build/          generated images (gitignored)

Roadmap

• Done: boot sector, serial output, stage 2 loader, serial REPL
• Next: int 16h keyboard input, then a Forth-style command language
• Later: real interrupt services (IVT + handlers), e820 memory map, booting an actual kernel

tasks.md has the complete list, including the ambitious bits.

License

MIT