Lab 1: Minix-style I/O without the VM

Generated folder: labs/rtc/

Lab 1 introduces the course mental model. A program talks to a small controller through registers, and those bytes only mean something once the programmer knows which bits matter. The device is the RTC/CMOS clock: a tiny register set, an observable protocol, and understandable errors.

The lab already teaches the habits used later: check status before trusting data, decode values by a configuration bit, return errors separately from output values, and keep C helpers small enough to inspect. lcom-ng keeps the controller-facing work and moves hardware behind a safe runtime.

What you will learn

• Why older PC devices used I/O ports.
• How to isolate and construct bit fields.
• Why a controller exposes status before data.
• How BCD differs from a binary integer.
• Why C APIs return a status code while filling caller-owned structures.

Plan

Read why I/O looked this way, then the port pair used by the RTC. Implement the bitwise helpers before reading date and time. The tasks list the required functions and the checks show how to validate them. Finish with modern hardware access.

TIP

Do the bit helpers first. They are pure C and build confidence before controller reads.