The keyboard controller

The i8042-style controller sits between the CPU and the keyboard. It exposes a small register interface and raises an event when a scancode byte is waiting.

Register	Role
status register	output-buffer state and error bits
output buffer	next scancode byte
command register	controller commands
IRQ line	keyboard event notification

The safe read sequence is: read status, confirm the output buffer is full, check error bits, read the output byte, and pass the byte to the scancode parser. The status read prevents empty-buffer reads. The error checks prevent corrupted bytes from becoming trusted input. The parser call keeps device I/O separate from scancode assembly.

Avoid collapsing this into a single "get key" helper too early. At this layer you get one byte from a controller stream. It may be a prefix, a command response, or part of a larger event.

IMPORTANT

Do not read output data just because your program wants input. Read only when the status register says data is available.