Hardware of the era

A PC game from 1985 to 2005 uses its hardware far more directly than a modern program. DOS games program the timer, the video card, the sound card and the joystick port themselves. Windows games of the late 1990s use DirectX or a card maker's own 3D API. The hardware a game was written for affects much of its code: the CPU's floating-point unit, the video mode, the sound chip, the 3D card's features.

When you rebuild such a game, you replace the hardware with modern equivalents. To do that exactly, you need to know what each piece of hardware did, how the game used it, and which of its details the player can see or hear.

Ask your agent

Find the hardware layer. Copy this prompt into your coding agent:

In my GameFrame project, find every place the game touches hardware.

1. Read docs/hardware/README.md and the pages for this game's devices.
2. In the disassembly, find IN, OUT and INT instructions and writes to A000, B800 and 0040.
   For a Windows game, list the imports from DirectX, Glide, OpenGL and WinMM.
3. Name the driver functions (set a mode, set a palette, play a sound, read the joystick).
4. List the values the game reads back from the hardware. They are inputs.
5. Propose one reference configuration (video, sound, input) and ask me to confirm it.

Pages

• CPUs and floating point: the x86 generations, the x87 FPU, MMX, 3DNow! and SSE, fixed point, timing loops, self-modifying code.
• 2D graphics: CGA, EGA, VGA, Mode 13h, Mode X, VESA, palettes and the vertical retrace.
• 3D accelerators: 3dfx and Glide, Rendition, PowerVR, S3, ATI, Matrox, NVIDIA, Direct3D and OpenGL, and software renderers.
• Sound: the PC speaker, AdLib and OPL FM synthesis, Sound Blaster, Gravis Ultrasound, MIDI devices, DirectSound, A3D and EAX.
• Memory, storage, input and networks: EMS, XMS and DOS extenders, CD audio, the game port, IPX, serial links and modems.

General rules for hardware code

1. Find every place the game touches hardware. In DOS games, search the disassembly for IN, OUT, INT and writes to segments A000, B800 and 0040. In Windows games, list the imports from DirectX, Glide, OpenGL, WinMM and the card makers' DLLs.
2. Label the driver layer. Most games wrap hardware access in a small set of functions (set a mode, set a palette, play a sample, read the joystick). Name them, and treat the rest of the game as their callers.
3. Decide what the port must copy. It must copy the picture and the sound the player perceives. It usually does not need to copy how the game produced them on the card. A frame drawn by Glide can be drawn by Vulkan, as long as it looks the same.
4. Keep what the game logic reads back. Some games read values from the hardware and use them in their rules: a timer count, the retrace state, a joystick reading, a sound position. Those values are inputs (Inputs).
5. Choose one reference configuration. The original looked and sounded different on different cards. Pick the configuration your project reproduces (for example "VGA, Sound Blaster 16, General MIDI through a Roland SC-55") and write it in the project's AGENTS.md.