Write to VGA Text Mode Buffer

Text Framebuffer at 0xB8000

VGA text mode maps an 80x25 array of character/attribute pairs at 0xB8000. Writing 0x0741 stores white-on-black A without a graphics driver.

Memory Layout

Each cell:

• Byte 0: ASCII code point
• Byte 1: foreground/background attributes

For example, row 2 col 5 lives at index (2 * 80 + 5) * 2 bytes from 0xB8000.

Why This Matters in Production

Writing directly to the VGA buffer at physical address 0xB8000 is exactly how BIOS, GRUB, DOS, and the early Linux console all rendered text for decades before framebuffer graphics took over. Forgetting to handle scrolling when the cursor passes row 24 is a classic bug that causes new kernel output to silently disappear off the bottom of the screen instead of appearing.

Debugging Checklist

Before you call the implementation done, walk failure modes on purpose. Test empty structures, single-element edge cases, maximum concurrency, and errno paths that must not crash the program. OS code usually fails in production when happy-path tests pass but invariants break under contention or memory pressure.

Implementation Notes

Keep structures small and name fields after kernel counterparts when possible. That lets you read man pages and kernel source side by side while you work. Print observable events during development; remove noisy logs once tests pass reliably.

For This Exercise

You will implement cursor movement, newline scroll, and colored kprintf output. The task asks you to wrap long lines without corrupting attribute bytes.