Add set_chr_mode() API for MMC3 CHR bank switching#307
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jonathanpeppers merged 6 commits intomainfrom Mar 21, 2026
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Co-authored-by: jonathanpeppers <840039+jonathanpeppers@users.noreply.github.com> Agent-Logs-Url: https://github.com/jonathanpeppers/dotnes/sessions/f65776e2-53fb-48e6-b892-9ae98a55c48d
Co-authored-by: jonathanpeppers <840039+jonathanpeppers@users.noreply.github.com> Agent-Logs-Url: https://github.com/jonathanpeppers/dotnes/sessions/f65776e2-53fb-48e6-b892-9ae98a55c48d
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[WIP] Add support for MMC3 mapper CHR bank switching
Add mmc3_set_chr_bank() API for MMC3 CHR bank switching
Mar 21, 2026
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Pull request overview
Adds a first-class mmc3_set_chr_bank(byte reg, byte bank) API to neslib and wires it through the transpiler so MMC3 (mapper 4) CHR bank switching can be emitted without manual poke() sequences.
Changes:
- Added
NESLib.mmc3_set_chr_bank(reg, bank)public API stub (with MMC3 CHR register docs). - Implemented IL dispatcher support to emit
$8000/$8001writes for MMC3 bank select/data. - Added a Roslyn-based test asserting the expected 6502 byte sequence and updated
PublicAPI.Unshipped.txt.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.
| File | Description |
|---|---|
| src/neslib/PublicAPI.Unshipped.txt | Declares the new public API surface for mmc3_set_chr_bank. |
| src/neslib/NESLib.cs | Adds the mmc3_set_chr_bank stub and XML documentation. |
| src/dotnes.tasks/Utilities/IL2NESWriter.ILDispatch.cs | Adds call-dispatch lowering that emits the MMC3 bank select/data writes. |
| src/dotnes.tests/RoslynTests.cs | Adds a regression test validating emitted bytes for constant reg/bank pairs. |
Follows nesdoug's set_chr_mode_X() convention but uses a register parameter instead of 6 separate functions. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
…/tests - Verify reg is a compile-time constant (LDA immediate); throw TranspileException otherwise - Remove dead bankIsStaticField branch (_lastStaticFieldAddress is never assigned) - Update XML docs to document full bank-select byte including mode bits - Add SetChrMode_SupportsLocalBankArg test for local variable bank argument Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Mar 21, 2026
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All 4 review comments addressed. API renamed from mmc3_set_chr_bank to set_chr_mode (nesdoug-style). All 569 tests pass.
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Add
set_chr_mode(byte reg, byte bank)API for MMC3 CHR bank switching, following nesdoug'sset_chr_mode_X()naming convention but with a register parameter instead of 6 separate functions.Emits inline 6502:
LDA #reg, STA $8000, LDA #bank, STA $8001set_chr_mode(byte reg, byte bank)stub with MMC3 register docsregmust be constant,banksupports constants and localsFixes #306