Lab 3 Tasks

Work in labs/kbd/. The goal is to build a reliable keyboard layer before you build application behavior on top of it. Keep the controller reads, parser state, and test-facing output separate enough that each part can be checked on its own.

Requested Functions

• int kbc_read_status(uint8_t *status)
• int kbc_read_output(uint8_t *byte)
• int kbc_write_command(uint8_t command)
• int kbd_process_byte(uint8_t byte)
• int kbd_get_scancode(uint8_t bytes[2], uint8_t *size, int *make)

Guided Gaps

Check output pointer arguments, ignore reads when no byte is available, detect controller error bits, store a pending 0xE0 prefix, and report make/break state without losing the original bytes. Command/ACK handling should stay separate from scancode parsing, because a command response is not a key event.

You also need to decide how callers observe "no complete scancode yet." That is not necessarily an error; it may simply mean the parser has seen the first byte of an extended sequence and is waiting for the next one.

IMPORTANT

Do not treat every byte as a complete scancode. Extended scancodes must be assembled before the API reports an event.

Common Mistakes

Common mistakes include clearing parser state too early, reporting a scancode before all bytes arrived, treating break codes as normal key presses, and reading output without checking status. Most of these are ownership mistakes: the program loses track of who owns the next byte, the current parser state, or the subscribed IRQ.

Next: checks and references.