CoffeePSX

Work-in-progress attempt at a PlayStation emulator.

Some games are fully playable, but some do not boot or have major issues.

Why?

Why write a PS1 emulator at all? For fun and learning, of course!

For a more interesting question, why is this a standalone emulator instead of a backend core in jgenesis?

Short version is that I wanted more freedom to experiment with the interface between the backend (the actual console emulator) and the frontend (the thing that displays frames / plays audio / etc). jgenesis has an interface that is designed around consoles like Genesis/SNES where from an emulation perspective it's massively preferable to render frames on the host CPU rather than the GPU. For later consoles like PS1/Saturn/N64/etc., there's a lot of benefit to rendering frames on the host GPU instead of the host CPU, and I wanted the interface freedom to make it possible to take advantage of that.

I'm also trying out some alternative forms of video/audio synchronization, which is a lot easier to do when there's only 1 backend core.

I may merge the two projects in the future - there are definitely ways to create a single API that will work for both 2D consoles and PS1 - but for the time being this is its own thing.

Status

Implemented

• CPU
  • Currently implemented using a plain interpreter; performance could be a lot better
• GTE (3D math coprocessor)
• GPU, with both software and hardware rasterizers
  • Hardware rasterizer uses wgpu with native extensions; should work on Vulkan, DirectX 12, and Metal (has not been tested on MacOS/Metal)
  • Hardware rasterizer supports higher resolutions up to 16x native as well as 24bpp high color rendering
  • Supports basic PGXP (Parallel/Precision Geometry Transform Pipeline), which reduces model wobble and texture warping in many 3D games
    • "CPU mode" is not yet implemented so the PGXP implementation is not compatible with some games (e.g. Spyro series, Metal Gear Solid, Resident Evil 3, Tony Hawk's Pro Skater series)
• SPU (sound processor)
• Most of the CD-ROM controller
• Support for loading CUE/BIN disc images, CHD disc images, and PS1 EXE files
• MDEC (hardware image decompressor)
• Hardware timers
• NTSC/60Hz and PAL/50Hz support
• Digital and analog controllers
• Memory cards

Not Yet Implemented

• Hotkey configuration
• DualShock rumble support
• Some sort of memory card management UI
• Additional graphical enhancements for the hardware rasterizer (e.g. PGXP CPU mode, texture filtering, downsampling)
• More efficient CPU emulation (cached interpreter, recompiler)
• More accurate timings for DMA/GPU/MDEC; some games that depend on DMA timing work, but timings are quite inaccurate right now
• Some CD-ROM functionality including infrequently used commands and 8-bit CD-XA audio
  • There are possibly no games that use 8-bit CD-XA audio samples?
• Various emulator enhancements like increased disc drive speed, CPU overclocking, rewind, save state slots
• Accurate timing for memory writes (i.e. emulating the CPU write queue)
  • It seems like maybe nothing depends on this?

Software Rasterizer AVX2 Dependency

The software rasterizer makes very heavy use of x86_64 AVX2 instructions. These have been supported in Intel CPUs since Haswell (Q2 2013) and AMD CPUs since Excavator (Q2 2015). There is a fallback rasterizer that does not use any x86_64 intrinsics but it is extremely slow and will probably not run 3D games at full speed.

The hardware rasterizer has no such dependency.

Build Dependencies

Rust

This project requires the latest stable version of the Rust toolchain to build.

SDL2

This project uses SDL2 for audio and gamepad inputs.

Linux (Debian-based):

sudo apt install libsdl2-dev

MacOS:

brew install sdl2

Windows:

• https://github.com/libsdl-org/SDL/releases (use a 2.x version)

Build & Run

To run the GUI:

cargo run --release

To run in headless mode (no GUI window, will exit when the emulator window is closed):

cargo run --release -- --headless -f /path/to/file.cue

To build with fat LTOs (link time optimizations), which slightly improves performance and decreases binary size but increases compile time:

cargo build --profile release-lto
# Executable located in target/release-lto/

Hotkey Bindings

• Save state: F5 key
• Load state: F6 key
• Fast forward: Tab key
• Pause: P key
• Step to next frame: N key
• Select hardware rasterizer: 0 key
• Select software rasterizer: - key (Minus)
• Decrease resolution scale: [ key (Left square bracket)
• Increase resolution scale: ] key (Right square bracket)
• Toggle VRAM view: ' key (Quote)
• Exit: Esc key

Screenshots