30 min codex-cli with GPT-5.2 hihg made fully working NES emulator in pure c with mapper 0.

Achieving a Fully Functional NES Emulator in Just 30 Minutes Using GPT-5.2 and Codex-CLI

Recent advancements in AI coding assistance have opened new horizons for rapid software development. In a notable experiment, a developer successfully built a fully operational Nintendo Entertainment System (NES) emulator in pure C within a mere 30-minute window, utilizing OpenAI’s GPT-5.2 and the Codex-CLI tool. This achievement demonstrates the potential for leveraging AI models to accelerate complex programming tasks, even within constrained timeframes.

The Development Journey

The developer’s process involved multiple iterations with varying GPT models and configurations, each yielding progressively improved results.

Initial Attempt: GPT-5 High-Quality Model (45 Minutes)

The first trial employed GPT-5 configured for high-detail code generation with a 45-minute session. Using Codex-CLI, the goal was to generate an NES emulator capable of running NES ROMs with minimal manual intervention. The outcome produced a program displaying only the game’s title screen without enabling gameplay—an indication that further refinement was needed.

Link to original attempt:
Reddit Post

Second Attempt: GPT-5 Medium Model (25 Minutes)

Next, the developer switched to GPT-5’s medium configuration, which balances detail and efficiency. This version managed to produce a working emulator for games with Mapper 0 (the simplest type), but with noticeable glitches. Although the software could launch and display game content, gameplay was hindered by graphical and functional inconsistencies.

Link to the second attempt:
Reddit Post

Final Success: 30-Minute Fully Functional Emulator

The breakthrough came with a targeted approach: leveraging GPT-5.2’s capabilities in a single, focused session. By allocating only 30 minutes and approximately 30% of a Plus account’s available hours, the developer generated a fully operational NES emulator in pure C, supporting Mapper 0 games without glitches. This version is capable of loading ROMs