0xrsydn/gameboy-rust
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feat(cartridge): add 32 KiB SRAM save memory

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Select it with --save-type sram (SaveDevice::Sram). The array is byte-wide,
starts erased, and repeats every 32 KiB through the 0x0e00xxxx save window.
A CPU byte store is staged and committed when its step completes, so failed
steps roll back and reads later in the step see the byte. Unlike Flash, SRAM
can be read from ROM code. Halfword/word access and DMA stay diagnostic until
the 8-bit bus behavior for those widths is verified.

SRAM shares the save-image API, host save files, and save states. Its device
code is new, so existing save states keep loading.

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 11:51:27 +07:00
commit 32eaffa0fe
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docs/usability-roadmap.md
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@ -69,7 +69,7 @@ Next implementation steps:
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.
3. Add SRAM separately when the independent candidate requires it; verify widths, mirroring, and waits first.
3. Byte-wide 32 KiB SRAM is now available with `--save-type sram`. Halfword/word SRAM access stays diagnostic until verified.
4. Resume the second-game run and implement demonstrated audio requirements rather than accepting writes without behavior.
## Development loop