retroDE_ps2/references/software_and_emulators.md

PS2 Software and Emulator References

This file tracks software-side sources that are useful for implementation planning, test generation, and behavioral cross-checking.

Homebrew SDK / Toolchain

ps2dev

The modern community toolchain entry point is ps2dev. As of this research pass, the project is still actively maintained and distributes a build/install flow for:

• ps2toolchain
• ps2sdk
• ps2sdk-ports
• gsKit

Why this matters for FPGA work:

• It gives us a realistic software stack for directed tests and homebrew smoke tests.
• It provides a path for EE-side and IOP-side sample programs.
• It gives us a straightforward way to assemble minimal bring-up artifacts without depending on commercial game software.

ps2sdk

ps2sdk is especially important because it reflects the software-visible split of the platform:

• ee/: EE-side APIs and startup.
• iop/: IOP-side modules and APIs.
• common/: shared definitions.
• samples/: useful test and bring-up material.

The README explicitly notes that the PS2 has two independent CPUs and that the source tree is split accordingly. That is not just a software organization detail; it mirrors the hardware architecture we would be trying to realize.

gsKit

gsKit is a low-level C interface to the Graphics Synthesizer and includes dmaKit for DMAC usage. It is useful for:

• GS initialization studies,
• GIF/DMAC packet expectations,
• simple graphics smoke tests,
• learning what a "minimal working GS path" looks like from software.

For staged bring-up, ps2sdk + gsKit may be one of the best ways to generate small, understandable graphics test payloads.

Emulator Landscape

PCSX2

PCSX2 is the longest-running open-source PS2 emulator in this source set. Its README describes the project as emulating PS2 hardware using:

• MIPS interpreters,
• dynamic recompilers,
• a VM that manages hardware state and PS2 system memory.

Why it matters:

• It is a strong reference for edge cases and practical compatibility behavior.
• Its memory subsystem and hardware models can point us toward the parts of the PS2 that real software stresses hardest.
• It is likely the deepest public implementation well for subtle behavior, even if an FPGA port should not blindly mirror emulator design choices.

One useful immediate note from pcsx2/Memory.cpp: the file header still carries an implementation-focused summary of the EE-visible RAM, scratchpad, and BIOS regions, which is a good signpost when cross-checking memory assumptions.

DobieStation

DobieStation is valuable because it also publishes a concise explanatory writeup for early PS2 emulator bring-up. The strongest planning takeaway from its "From Bits to Pixels" article is that first-frame graphics on PS2 already requires:

• a correct-enough memory map,
• EE execution,
• DMAC channel behavior,
• GIF transfer handling,
• GS-side behavior.

That writeup is useful because it compresses the "minimum viable visible PS2" problem into a few concrete dependencies.

Play!

Play! is useful as a contrasting design point:

• it uses a built-in HLE BIOS instead of requiring an external BIOS dump,
• it targets many host platforms including mobile and web,
• it documents some practical issues around JIT and page protection.

Even though a retroDE FPGA core is unlikely to follow Play!'s HLE BIOS path, Play! is still a good reminder that firmware strategy is a first-order architectural decision, not an implementation detail.

What these projects are good for

Best sources for behavior questions

• PCSX2
• DobieStation
• ps2tek

Best sources for test payloads and small samples

• ps2sdk
• gsKit
• broader ps2dev stack

Best sources for boot and user-visible software assumptions

• dumped BIOS behavior as described in ps2tek
• emulator boot flows
• homebrew SDK samples

Likely validation strategy

If this becomes a real implementation effort, these software sources suggest a validation ladder:

1. Run tiny EE-side tests that only touch RAM and simple I/O.
2. Run gsKit-style minimal graphics payloads for first visible output.
3. Run BIOS-only boot traces and compare major milestones with emulator traces.
4. Add IOP/SIF-sensitive homebrew.
5. Only then move into complex game software.

Source Pointers

• ps2dev: https://ps2dev.github.io/
• ps2dev repo: https://github.com/ps2dev/ps2dev
• ps2sdk repo: https://github.com/ps2dev/ps2sdk
• gsKit repo: https://github.com/ps2dev/gsKit
• PCSX2 repo: https://github.com/PCSX2/pcsx2
• PCSX2 memory source: https://raw.githubusercontent.com/PCSX2/pcsx2/master/pcsx2/Memory.cpp
• DobieStation repo: https://github.com/PSI-Rockin/DobieStation
• DobieStation wiki article: https://github.com/PSI-Rockin/DobieStation/wiki/Making-a-PS2-Emulator%3A-From-Bits-to-Pixels
• Play! repo: https://github.com/jpd002/Play-