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Implement MMC3 variant where nametable mirroring is controlled via bit 7 of CHR bank values instead of the $A000 register, enabling single-screen and diagonal mirroring modes. Used by games like Armadillo, Pro Sport Hockey, and Goal! Two. Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
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Summary
Implements mapper 118 (TxSROM), an MMC3 variant where nametable mirroring is controlled via bit 7 of CHR bank register values instead of the standard $A000 mirroring register. This enables single-screen and diagonal mirroring modes that standard MMC3 cannot produce.
The mapper is used by games like Armadillo, Pro Sport Hockey, and Goal! Two.
Implementation Details
Testing
All existing tests pass (445 passed, 0 failed).