ppsspp/AGENTS.md

PPSSPP Agent instructions

These rules apply to this repository by default.

Ignore the folder ai_instructions in the root directory, it's old stuff from contributors.

General instructions

1. Keep style changes minimal unless requested. Follow existing code patterns and conventions.
2. Keep cross-platform parity in mind when changing shared code. See below for more multiplatform tips

Core Safety Checks

1. For HLE, CPU, GPU, timing, threading, and memory changes, call out regression risks explicitly.
2. Consider savestate compatibility when changing serialized state.

Build and Validation

To verify that things build on Linux/Mac, use ./b.sh --debug. For Windows, use the Visual Studio solution in the Windows subdirectory. Do not run unit test (I will add instructions for how to run them later).

Multiplatform considerations

The emulator has multiple platform-specific entry points. Some of these will be merged or removed in the future, but are all still there. To verify that a change works, technically we need to compile for all these systems, but in practice we'll just compile locally and test the platform we are currently on, and let CI handle the cross platform considerations.

System_-prefixed wrapper functions implement kind of a platform wrapper for some functionality, and are implemented in the following list of files for each system. If we change one, we need to change them all.

Windows/main.cpp ios/main.cpp SDL/SDLMain.cpp UWP/PPSSPP_UWPMain.cpp Qt/main.cpp android/jni/app-android.cpp libretro/libretro.cpp

Headless and unittest builds

We have additional PPSSPPHeadless and unit test builds (/headless and /unittest), that have their own separate main functions (and also stub out most of the System_ functions as needed). Take these into account when making cross platform changes.

New unit tests are added by listing them in availableTests in unittest.cpp. If they are large, put them in separate files in the unittest subdirectory. Remember to update both CMakeLists.txt and the visual studio project.

pspautotests are a large set of tests of the PSP OS's API surface, and thus tests our HLE implementation.

See docs/pspautotests.md for a workflow for running pspautotests and improving PPSSPP with the results.

Adding HLE modules

HLE module implementations live in Core/HLE/sce<ModuleName>.cpp / .h (e.g. sceOpenPSID.cpp, scePauth.cpp are good small examples to copy from). A module is a const HLEFunction <name>[] table of {nid, &WrapX_YYY<func>, "funcName", retChar, argString} entries, registered via RegisterHLEModule("<name>", ARRAY_SIZE(table), table) inside a Register_<name>() function declared in the header.

• FunctionWrappers.h has generic WrapX_YYY<func> templates for common signatures (return type X, args YYY) - add new wrappers there if you need a new signature.
• Format string legend for the retmask/argmask chars: x = u32 (shown as hex), i = int/s32, f = float, X = u64, I = s64, v = void.
• For functions of genuinely unknown purpose (only known by NID), name them <moduleName>_<NID> and stub them with return hleLogError(Log::HLE, 0, "UNIMPL"); - an established pattern (see scePauth.cpp, sceOpenPSID.cpp).
• New modules must be registered at the very end of the registration function in Core/HLE/HLETables.cpp (look for the // add new modules here. comment near the end of that function) - not inserted alphabetically/logically among the existing Register_*() calls. Module registration order affects numeric IDs used in savestates, so inserting a new module earlier in that list would break save-state compatibility for saves made with older builds.
• Remember to add any new .cpp/.c file to five places: Core/CMakeLists.txt, Core/Core.vcxproj, Core/Core.vcxproj.filters, android/jni/Android.mk, and libretro/Makefile.common. New .h files only need the first three (Android.mk/Makefile.common are plain compiled-source lists so headers don't go in them). Only the CMakeLists.txt change can be verified from a Linux/Mac build - the rest can't be build-tested here, so double check them by hand against how an existing neighboring file (e.g. sceVaudio.cpp) is listed in each.

WebSocket debugger

PPSSPP has a JSON/WebSocket debugger and automation API (connect, read/write memory, search memory for values or byte patterns, set breakpoints, step the CPU, label data symbols, read GPU state, inject input, tail logs, etc.), served on the same port as Remote ISO sharing at /debugger with subprotocol debugger.ppsspp.org. Implementation is in Core/Debugger/WebSocket.cpp and Core/Debugger/WebSocket/*Subscriber.cpp (one file per feature area, each documented at the top). Enable it via Settings > Tools > Developer Tools > "Allow remote debugger", RemoteDebuggerOnStartup in the config, or --debugger=PORT on the command line (0 = pick a port automatically) - works on both the application and headless builds. On headless it also forces a break at start (startBreak), so the CPU halts before anything runs. The bundled web GUI at /debugger/ comes from the assets/debugger submodule (unknownbrackets/ppsspp-debugger, bundled branch).

Before touching this interface, read docs/WebSocketDebugger.md - it has the full protocol reference and event catalog (including which events are read-only vs. require cpu.stepping first). Don't guess event names or parameters from memory; the doc (and each *Subscriber.cpp file's per-handler comments) is the source of truth, and new events get added over time (e.g. memory.search, hle.data.*).

When adding new commands, don't forget to update docs/WebSocketDebugger.md,

To quickly get a live session going for manual testing (e.g. after adding/changing an event): build PPSSPPWindows (see Build and Validation above), then run it with --debugger=PORT and something that keeps running/looping so the CPU stays alive, so requests get a response instead of "CPU not started"/"CPU not active" errors. Any homebrew or game works; PSP homebrew isn't checked into this repo, so if you don't already have something installed under memstick/PSP/GAME/, ask the user for a .iso/.cso/.elf/EBOOT.PBP to boot, or to install one via the in-app Homebrew Store. Watch the log output (--log=somefile.log) for the line Listening on port N, then point Tools/wsdbg/ at that port (cargo run -- N <event> [key=value...] for one-shot, or cargo run -- N for a REPL). Most mutating events (hle.func.*, hle.data.*, memory writes while paused, etc.) require the CPU to be stopped first - send cpu.stepping and cpu.resume to pause/unpause.

Alternatively use the headless build, Windows/{arch}/Debug/PPSSPPHeadless.exe or build/PPSSPPHeadless on CMake-based platforms. Where arch is x64 or ARM64.

Debugging and breakpoint considerations

It might be worth trying the interpreter - all types of breakpoints are the most reliable with this CPU backend. The JITs are much, much faster and in theory also support breakpoints, but especially from websockets there seem to be trouble.

Quick rebuild on Linux

You don't need to do ./b.sh --debug to verify every single little change, instead use this shortcut:

cd build ; make -j32; cd ..