pomodoro

This project was built as a practice project for CSC 204 – x86 Assembly, with the goal of going beyond toy examples and writing a real, interactive system-level program.

pomodoro is a Pomodoro timer implemented as a Terminate-and-Stay-Resident (TSR) program in real-mode DOS. It hooks directly into hardware interrupts to provide a background countdown timer with work and rest cycles, rendered in VGA text mode.

The project focuses on low-level control, timing accuracy, and safe interrupt handling.

Features

• Countdown Timer Starts at 25 minutes for work sessions and decrements using ~55ms ticks driven by the hardware timer.

• Work & Rest Cycles Supports active work sessions (25 minutes), short breaks (5 minutes), and long breaks (15 minutes after every 4 cycles).

• Interrupt-Driven Controls Hooks into:

  • IRQ0 (Timer interrupt) for precise time tracking
  • IRQ1 (Keyboard interrupt) for real-time user input

• Keyboard Controls

  • S, C, or Space: Start / toggle pause
  • P: Pause / unpause
  • R: Reset timer to 25:00:000

• VGA Text Display Real-time MM:SS:MS display rendered directly in 80×25 text mode.

• TSR Execution Runs in the background as a memory-resident program.

Running the Project

The program is designed to run in a DOS-compatible environment such as DOSBox.

nasm pomodoro.asm -o pomodoro.com
pomodoro.com

Once started, the timer responds instantly to keyboard input while remaining resident in memory.

Key Learnings

• Real-mode interrupt handling and safe IRQ chaining
• Writing TSR programs without breaking DOS input or timing
• Dealing with NASM constraints such as short jump ranges
• Precise timing using the hardware timer
• Direct manipulation of VGA text memory

This project was an exploration of how much functionality can be built with minimal abstractions—and how unforgiving low-level systems programming can be.