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msx-vdp-audit

Validate MSX video emulation for the TMS9918A/TMS9928A/TMS9929A VDP family in EMULATORS, including ports

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Commnets/EMULATORS
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Files included (3)

  • SKILL.md2.9 KB
  • agents/openai.yaml225 B
  • references/vdp.md7.5 KB

SKILL.md (original)

Review the instructions the agent will receive before you install.

MSX VDP Audit

Core Workflow

Use this skill to audit whether EMULATORS models the MSX1 VDP family as a port-driven video chip with separate VRAM and TMS9918A-compatible side effects.

  1. Read references/vdp.md before making claims or edits.
  2. Inspect the relevant implementation paths first:
    • include/MSX/VDP.hpp, src/MSX/VDP.cpp
    • include/MSX/Screen.hpp, src/MSX/Screen.cpp
    • include/MSX/PortManager.hpp, src/MSX/PortManager.cpp
    • include/MSX/Commands.hpp, src/MSX/Commands.cpp
    • include/TEXASINSTRUMENTS/TMS99xxFamily/TMS99xxFamily.hpp, src/TEXASINSTRUMENTS/TMS99xxFamily/TMS99xxFamily.cpp
    • include/TEXASINSTRUMENTS/TMS99xxFamily/TMS99xxFamilyRegisters.hpp, src/TEXASINSTRUMENTS/TMS99xxFamily/TMS99xxFamilyRegisters.cpp
  3. When changing C++ code, also use $emulators-framework-cpp-style.
  4. Confirm the intended chip/model first. TMS9918A/TMS9928A/TMS9929A behavior is not the same as V9938/V9958 behavior.
  5. Treat port protocol, register side effects, VRAM table addressing, and status reads as correctness requirements, not renderer details.

Audit Priorities

Prioritize correctness in this order:

  • Port #98/#99 protocol, including two-byte control writes, address latch, register writes, status reads, and VRAM auto-increment.
  • Status register flags and clear-on-read behavior for VBlank interrupt, fifth-sprite overflow, and sprite collision.
  • Register R0-R7 write masks, read/write exposure, and mode-bit combinations.
  • Pattern name, color, pattern generator, sprite attribute, and sprite pattern table base calculations, including Graphics II masking quirks.
  • Text, Graphics I, Graphics II, and Multicolor mode rendering rules.
  • Sprite evaluation: Y coordinate offset, terminator, size/magnification, priority, 4 sprites per scanline, overflow index, collision flag.
  • PAL/NTSC frame timing and VDP INT wiring to the Z80/BIOS.

Validation Hints

Useful local anchors:

  • emulators/MSXPrograms/KEY/GRAPHICS1.key
  • emulators/MSXPrograms/KEY/SPRITES1.key
  • emulators/MSXEmulator*/MSX.fmt
  • emulators/MSXEmulatorC/TexasInstruments.hlp
  • VDP monitor commands in src/MSX/Commands.cpp

For visual bugs, reduce to a small VRAM/register setup before comparing whole games. For port bugs, write Z80 tests that touch #98/#99 directly and also through BIOS routines such as WRTVDP, RDVRM, WRTVRM, SETRD, and SETWRT.

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