Introduction

psp-js is a PSP emulator written in TypeScript that runs in the browser. It uses high-level emulation (HLE), the same approach as PPSSPP: instead of running a real PSP BIOS, the system calls a game makes are intercepted and implemented directly in TypeScript. No BIOS ROM is required.

Ridge Racer running in psp-js, captured from the in-game replay.

What it does

It boots real commercial games, taking them through the full pipeline a PSP would:

• Decrypts KIRK-encrypted EBOOT.BIN modules and decompresses them.
• Loads games from ISO or PBP containers.
• Runs the MIPS Allegrex CPU and the VFPU (vector FPU).
• Renders the GE (Graphics Engine / GPU) over WebGL, with a software rasterizer as an alternative.
• Decodes ATRAC3+ audio and MPEG/PSMF video for in-game sound and cutscenes.
• Persists savedata in the browser.

How HLE works here

A PSP game runs as MIPS code, but when it needs the operating system (to create a thread, allocate memory, draw to the screen, read a file) it issues a syscall instruction. In real hardware that traps into the kernel. Here, the CPU flags the syscall and the HLE kernel dispatches it to a TypeScript handler that implements the behaviour. The behaviour is matched against the PPSSPP source, which is treated as the authoritative reference for PSP behaviour.

See Syscall Flow & ABI for the mechanics.

Where it runs

• Browser is the main target. A Vite and Lit frontend hosts the game library, input mapping, debug panel, and the canvas. The GE renders over WebGL and audio plays through an AudioWorklet.
• Headless (Node) runs the same emulator core under tsx and vitest for diagnostics and tests. There is no WebGL in Node, so the GPU uses the software rasterizer.

Target hardware

The emulator models the PSP-2000/3000 (Slim):

Component	Value
RAM	32 MB by default, 64 MB for games that request it (0x08000000)
VRAM	2 MB (0x04000000)
CPU	222 MHz default; games switch to 333 MHz via scePowerSetClockFrequency
Display	480 × 272

If you just want to play, head to Running Games. To build the project, see Getting Started; for the big picture, Architecture.