memory: A4000 motherboard expansion space + CPU-slot accelerator RAM

[LinuxJedi]

Summary

Two new reaches of the big-box memory map, building on the Ramsey motherboard RAM from #242:

• Motherboard RAM expansion space ($04000000-$06FFFFFF, A4000). The [memory] motherboard bank still ends at $08000000 and grows downward, but on the A4000 (gated on Ramsey-07) it can now grow past Ramsey's four-bank 16M into the expansion window: whole 4M banks up to 64M, which reaches exactly $04000000. The A3000 stays capped at Ramsey's own 16M, and the control register keeps describing the fully populated 1Mx4 geometry -- it has no way to say more, and on real hardware the expansion decode would not go through Ramsey's geometry either.
• CPU-slot (accelerator) fast RAM ($08000000-$0FFFFFFF). A new [memory] accelerator / --accelerator bank, Memory::accel_ram, starting at $08000000 and growing upward through the coprocessor-slot space, up to 128M (ending at $10000000, where Zorro III space begins; Z3 boards configure at $40000000, so no overlap). This is the RAM an accelerator/CPU board carries, so it is gated only on a 32-bit CPU -- an accelerated A1200 config takes it too -- and any whole number of megabytes fits.

Surfaces: the new bank decodes through PlainMemRegion in every CPU access path at uncontended external speed, cacheable by both CPU caches like expansion RAM; peek_word_any / writable_ram_regions reach it for the debugger, CCP, and GDB stub. The launcher Memory tab gains an Accelerator RAM row (greyed "needs 32-bit CPU") and A4000-only 32M/64M motherboard presets, with both banks dropped on a CPU downgrade to a 24-bit part so the emitted config still validates. MachineDescriptor carries the new size for the savestate shape guard and STATE_VERSION moves to 36. Docs: configuration.md, internals/peripherals.md, copperline.example.toml, --help.

Verification

Booted the real Kickstart 3.1 A4000 ROM and walked exec's memory list (asset-gated tests + a live control-protocol session):

• --motherboard 64M: MemHeader $04000020-$08000000, attrs $0505 (PUBLIC|FAST|LOCAL|KICK) -- Kickstart's top-down probe walks the whole expansion window.
• --accelerator 64M: MemHeader $08000020-$0C000000; exec relocates ExecBase into the CPU-slot bank when it is the best memory.
• Odd totals size exactly: --motherboard 20M --accelerator 24M lists $06C00020-$08000000 and $08000020-$09800000.

tests/mb_ram.rs grows two more asset-gated #[ignore] integration tests pinning the 64M motherboard and CPU-slot probes (~1.7s total in release; skip cleanly without the ROM). New unit tests cover the expansion-window bounds and $04000000 base math, the accelerator bank fit/reset/refusal, config validation for both banks (A4000-only gate, 4M steps, megabyte granularity, 24-bit CPU rejection), the launcher gates and presets, and a CPU-level test showing a 68030 store lands at $08000000 while a 68000's 24-bit bus wraps past it.

cargo test (1716 unit tests + suites), cargo clippy --all-targets, and cargo fmt --check are all clean.

[Copilot]

Pull request overview

This PR extends Copperline’s big-box memory map by (1) allowing the A4000 motherboard RAM bank to grow downward through the $04000000-$06FFFFFF expansion window (up to 64 MiB) and (2) adding a new CPU-slot “accelerator” fast RAM bank at $08000000 growing upward (up to 128 MiB). It wires the new bank through CPU decode, debugger/control-protocol memory access, launcher/config surfaces, savestate shape/versioning, and documentation, with new unit + asset-gated integration tests covering the expected Kickstart probe behavior.

Changes:

• Expand A4000 motherboard RAM sizing beyond Ramsey’s 16 MiB limit into the reserved expansion window (up to 64 MiB, gated on Ramsey-07).
• Add CPU-slot accelerator RAM ([memory] accelerator / --accelerator) at $08000000 (up to 128 MiB, gated on 32-bit CPUs) across CPU access, debugger helpers, and UI.
• Update savestate version/descriptor + tests and refresh docs/example config/help to describe the new/expanded banks.

Reviewed changes

Copilot reviewed 25 out of 25 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/mb_ram.rs	Adds ROM-asset-gated integration tests that assert Kickstart sizes the expanded motherboard window and CPU-slot RAM.
src/zorro_device.rs	Updates test Memory construction to include the new accel_ram field.
src/z3660.rs	Updates multiple test Memory constructions to include accel_ram.
src/wasmboard.rs	Updates test Memory construction to include accel_ram.
src/video/window/tests.rs	Updates app test machine Memory construction to include accel_ram.
src/video/launcher.rs	Adds launcher field/row/presets for accelerator RAM; adds A4000-only motherboard expansion presets and CPU gating/drop behavior.
src/savestate.rs	Bumps STATE_VERSION to 36 and updates tests/descriptors to include accelerator RAM sizing.
src/ramsey.rs	Documents/locks Ramsey control-register geometry behavior for >16 MiB motherboard totals and tests it.
src/memory.rs	Raises motherboard cap to 64 MiB, introduces accel_ram + fitting/reset logic and bounds constants/tests.
src/main.rs	Adds --accelerator CLI parsing plus help text, and updates placeholder Memory initialization.
src/gdbstub.rs	Updates test Memory construction to include accel_ram.
src/filesys.rs	Updates test Memory construction to include accel_ram.
src/emulator.rs	Fits/logs accelerator RAM during machine build and updates test Memory constructions.
src/cpu.rs	Adds PlainMemRegion::AccelRam decode + caching/debugger write support and a CPU-level test for 32-bit vs 24-bit reach.
src/control.rs	Updates test emulator Memory construction to include accel_ram.
src/config.rs	Adds config surface/override/raw field for [memory] accelerator, validation, descriptor plumbing, and tests; expands motherboard validation to A4000 expansion window.
src/cdtv.rs	Updates test Memory construction to include accel_ram.
src/bus/tests.rs	Updates bus test Memory construction to include accel_ram.
src/bus.rs	Extends writable_ram_regions and peek_word_any to include accelerator RAM.
src/a4091.rs	Updates test Memory construction to include accel_ram.
src/a2091.rs	Updates test Memory construction to include accel_ram.
src/a2065.rs	Updates test Memory construction to include accel_ram.
docs/internals/peripherals.md	Documents the A4000 motherboard expansion window behavior and the new accelerator RAM bank.
docs/guide/configuration.md	Documents new [memory] accelerator / --accelerator and A4000 motherboard expansion sizing.
copperline.example.toml	Adds commented example/config notes for accelerator RAM and updated motherboard expansion behavior.

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