0xrsydn/gameboy-rust
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feat(cartridge): add 512-byte and 8 KiB serial EEPROM saves

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Select them with --save-type eeprom512 or eeprom8k. The part follows GBATEK's
protocol on Game Pak data bit 0: DMA3 sends one bit per halfword, '11' +
address + '0' requests a 64-bit block that reads back after four dummy bits,
and '10' + address + data + '0' writes one. A write reports busy for a nominal
108,368 cycles before the block is stored. 8 KiB parts decode the low 10
address bits. ROMs above 16 MiB map EEPROM only at 0x0dffff00..0x0dffffff.

Bits shift out only inside machine steps, so failed steps roll back. CPU
stores, byte/word accesses, CPU reads during a read-out, and malformed or
overlapping requests are diagnostics. Blocks are stored first-bit-as-MSB,
matching common .sav layouts, and work with save files and save states.

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 12:06:17 +07:00
commit 652ea397f2
15 changed files with 828 additions and 24 deletions
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docs/architecture.md
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@ -51,6 +51,8 @@ The repository is a Cargo workspace with three crates:
| `crates/gba-core/src/cartridge.rs` | Explicit GPIO/RTC selection, ROM read overlay, pin directions, caller-clock routing, and bounded diagnostics |
| `crates/gba-core/src/cartridge/flash.rs` | Explicit save devices, Macronix IDs/banks, delayed program/erase, bounded DQ7 polling, and staged mutations |
| `crates/gba-core/src/cartridge/sram.rs` | 32 KiB byte-wide SRAM, mirrored offsets, one staged byte per step, and its save-state section |
| `crates/gba-core/src/cartridge/eeprom.rs` | Serial EEPROM request decoding, 68-bit read-out, nominal write busy time, block commits, and its save-state section |
| `crates/gba-core/tests/eeprom.rs` | DMA3 EEPROM bitstreams, busy polling, 10-bit addressing, large-ROM window, diagnostics, and mid-read-out save states |
| `crates/gba-core/tests/rom_bus.rs` | Game Pak reads beyond the ROM chip in every window, trimmed-image gaps, strict host/fetch reads, and DMA sources |
| `crates/gba-core/tests/sram.rs` | SRAM selection, mirroring, byte stores/loads from ROM code, SWPB, width/DMA diagnostics, and save states |
| `crates/gba-core/tests/flash.rs` | Erased/supplied images, chip IDs, all bank addresses, invalid commands, reset limits, DMA rejection, and RTC independence |