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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/status.md
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@ -82,6 +82,7 @@ Update this file when a feature lands or a limit is removed.
- Cartridge GPIO and Flash controller changes participate in CPU/DMA rollback and block-store preflight without modifying ROM bytes.
- Explicit Macronix Flash64/Flash128 identification, bank selection, delayed byte programming, sector/chip erase, and nominal DQ7 polling.
- Transactional Flash completion and modification tracking, with exact-size core image loading and inspection.
- Explicit 32 KiB byte-wide SRAM (`--save-type sram`), mirrored through the save window and readable from ROM code.
- Optional desktop `--save-file` loading and clean-exit persistence, with exclusive locks, atomic installation, and unique previous-image backups.
- Original ROM save/restart/load checks across processes, including native-window persistence on Darwin arm64.
- Whole-machine [save states](hardware/save-states.md): `Machine::save_state`/`load_state` with image and cartridge identity checks, a checksum, and verify-before-mutate loading; ROM windows bind F5 (save) and F9 (load) to a `--state-file` slot.
@ -155,7 +156,7 @@ Individual fetch timing, hardware-accurate work cutoffs, video-bus contention, a
ROM windows offer opt-in Darwin audio output with `--audio` and explicit save persistence with `--save-file`.
The [Flash subset](hardware/saves.md) supports programming and erase with nominal delays and bounded DQ7 polling.
Flash timing, STOP clocking, and cancellation are not hardware-verified. Wider accesses and unverified busy addresses remain diagnostic.
SRAM, EEPROM, other manufacturers, autosave, crash recovery, and game-level save transactions remain unsupported.
EEPROM, other Flash manufacturers, SRAM halfword/word access, autosave, crash recovery, and game-level save transactions remain unsupported.
Persistence is tested on Darwin arm64 with original programs, not yet with external-game saves.
The optional [cartridge GPIO/RTC subset](hardware/cartridge-gpio.md) supports calendar/control transfers and explicit clock updates, selected with `--rtc` in ROM modes.
RTC persistence, interrupts, invalid-date correction, physical subsecond timing, GPIO aliases, and byte writes remain unsupported or unverified.