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fix(memory): ignore CPU and DMA writes to the Game Pak ROM windows

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Stores to 0x08-0x0c returned ReadOnly and stopped the machine. Hardware ignores
them, and a second game's boot code stores to a ROM mirror. Emulated writes now
pay their bus cost and change nothing. The 0x0d window stays a diagnostic until
EEPROM is modeled there, and host writes stay strict.

Tests that used a ROM store as their failing write now cross an ignored ROM
word into the 0x0d window.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HhfHfHEuzv2AUTd6erW1gU
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0xrsydn 2026-10-14 08:26:03 +07:00
commit 258fbff2fa
25 changed files with 86 additions and 74 deletions
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docs/usability-roadmap.md
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@ -65,7 +65,7 @@ A reproducible source build or an accessible upstream ROM is needed before recor
Next implementation steps:
1. Visible startup/menu progress is established: attract mode reaches the start menu and Birch dialogue, and sparse taps reach the in-game start menu by 12,000 frames ([probe](research/emerald-visible-progress.md)).
The first demonstrated second-game failure is a boot-init halfword store to ROM mirror `0x09fe2ffe` (recorded, not fixed).
The first demonstrated second-game failure is a boot-init halfword store to ROM mirror `0x09fe2ffe`. ROM-window writes are now ignored; reads past the image end remain diagnostics.
Use original regressions for any hardware correction; do not invent connected serial devices.
2. Validate an external game's completed save/restart/load cycle using a disposable `--save-file` path.
Refine nominal Flash timing and polling only with independent evidence and original regressions.