shell-patcher

Replaces the shell binary in a PlayStation BIOS ROM with an arbitrary PS-EXE, in the browser. One self-contained .html you can copy anywhere and open offline. No server, no install, no network.

Written by spicyjpeg.

What it does

Given a 512 KB BIOS image and a PS-EXE, it overwrites the shell region at 0x18000 with a small self-relocating stub followed by the executable body. The stub copies the body to the load address in the executable's header, flushes the instruction cache through A0(44h), sets $gp and $sp, and jumps to the entry point. The shell region is 0x4c000 bytes, so that is the ceiling on stub plus payload.

Two optional overrides are written before the copy runs, so they take effect before any of the executable does:

• Main RAM configuration, stored to 0x1F801060. See the memory control page for the values.
• VRAM size, sent as GP1(09h). Bit 0 gates the second 1 MB bank: with it clear every Y coordinate wraps inside the lower megabyte, with it set the full 10-bit Y range is addressable. Only meaningful on a board that has the upper bank populated.

Deploying

There is no build step. index.html is the artifact; the Pages workflow uploads it as it stands.