msx-system-audit

name	msx-system-audit
description	Validate general MSX system emulation in EMULATORS, including BIOS-facing behavior, Z80/VDP interrupt wiring, standard I/O ports, PPI 8255 ports

MSX System Audit

Core Workflow

Use this skill to audit whether EMULATORS behaves like a real MSX machine at the system-integration level.

1. Read references/system.md before making claims or edits.
2. Inspect the relevant implementation paths first:
   • include/MSX/MSX.hpp, src/MSX/MSX.cpp
   • include/MSX/Model.hpp, src/MSX/Model.cpp
   • include/MSX/PortManager.hpp, src/MSX/PortManager.cpp
   • include/MSX/PPI8255.hpp, src/MSX/PPI8255.cpp
   • include/MSX/PPI8255Registers.hpp, src/MSX/PPI8255Registers.cpp
   • include/MSX/OSIO.hpp, src/MSX/OSIO.cpp
   • include/MSX/FileIO.hpp, src/MSX/FileIO.cpp
   • emulators/MSXEmulator*, emulators/MSXPrograms, and docs/MSXData
3. When changing C++ code, also use $emulators-framework-cpp-style.
4. Use $msx-memory-map-audit for slot/subslot or mapper issues, $msx-vdp-audit for TMS9918A behavior, and $msx-sound-audit for PSG/AY/YM behavior.
5. Separate generic chip behavior from MSX-specific wiring. The 8255, AY-3-8910, and TMS9918A all have generic semantics, but MSX assigns their ports and some bits very specifically.

Audit Priorities

Prioritize correctness in this order:

• Standard I/O decode and dispatch: VDP #98-#9B, PSG #A0-#A2, PPI #A8-#AB, printer #90-#91, memory mapper #FC-#FF when present.
• PPI #A8 primary-slot register read/write and propagation into the memory system.
• PPI #A9/#AA keyboard matrix read path, including active-low keys and row selection.
• PPI #AA cassette motor/output, CAPS LED, and key-click output bits; #AB bit set/reset command behavior.
• VDP interrupt wiring to Z80 INT and BIOS interrupt/hook behavior.
• PSG GPIO cooperation with joystick ports, cassette input, keyboard layout bit, and Kana LED.
• Model-specific configuration: BIOS ROMs, RAM size, language/keyboard layout, PAL/NTSC video standard, VDP/PSG/PPI instances, and optional devices.

Validation Hints

Prefer small port-level or BIOS-level programs over whole-game comparisons. Useful local anchors include:

• emulators/MSXPrograms/KEY/*.key
• emulators/MSXEmulator/MSXSysVars.txt
• emulators/MSXEmulatorC/MSXSysVars.txt
• emulators/MSXEmulator*/bios/*.rom
• docs/MSXData/Keyboard*.jpg
• tests/TestZ80

When reporting a finding, identify the I/O port or BIOS-visible state, the expected MSX wiring, and the exact class or method that diverges.