Write a PS/2 Keyboard Driver

PS/2 Scancode Path

Keyboards send scancode bytes on IRQ1 from the 8042 controller. Make/break codes map through translation tables to ASCII for simple text mode shells.

Controller Protocol

Read path:

• Wait for output buffer full bit in status port 0x64
• Read scancode from data port 0x60
• Translate set1/set2 with shift/ctrl modifiers

For example, scancode 0x1E press with shift held may yield uppercase A in your lookup table.

Why This Matters in Production

The PS/2 scan-code translation you implement here , make codes, break codes, the shift/caps-lock XOR trick , is exactly what every BIOS and early Linux console driver did before USB HID keyboards became standard. Confusing a break code for a make code is a classic bug that makes a kernel think a key is still held down forever after it's released.

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 handle IRQ1, maintain modifier state, and push translated characters into a ring buffer. The task asks you to ignore break codes without duplicating key events.