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feat(input): implement KEYCNT keypad interrupt control

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Add a dependency-free keypad state machine in gba-core, map KEYCNT, latch IF bit 12, and wake HALT through the existing interrupt gates. Sample complete CPU/DMA control writes once so transient byte values cannot create false requests.

Document the mGBA-style polling policy and its unverified hardware retrigger limits. Cover every button-state/selection pair, register masks, repeated requests, byte/word writes, failed-store isolation, DMA priority, ARM/Thumb IRQ return, BIOS IntrWait, and retained BIOS reset state.

Follow the restructured workspace and modular documentation. Validated on Darwin arm64: workspace and core/demo tests pass in debug and release, with Clippy, rustdoc, ten native window smoke tests, and terminal demos passing.
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0xrsydn 2026-10-05 18:00:46 +07:00
commit 597b02881b
14 changed files with 710 additions and 21 deletions
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docs/hardware/video.md
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@ -8,7 +8,9 @@ Rendering behavior implemented in `crates/gba-core/src/video/`, plus button inpu
`GREENSWAP` at `0x04000002` exchanges the green channels of adjacent pixel pairs when bit zero is set.
`KEYINPUT` at `0x04000130` exposes ten active-low buttons. Unused bits read as zero; writes are ignored.
`Memory::set_buttons(Buttons)` supplies pressed-high host input. The I/O layer converts it to active-low register bits.
`KEYCNT` and keypad IRQs are not implemented; accesses to KEYCNT return unmapped-memory diagnostics.
`KEYCNT` at `0x04000132` selects buttons, OR/AND matching, and keypad interrupt enable.
Input samples and control writes can latch IF bit 12 and wake HALT without advancing the clock.
See [keypad interrupt control](timers-irq.md#keypad-interrupt-control) for the sampling policy and limits.
Video RAM starts at `0x06000000` and contains 96 KiB.
Its 128 KiB mirror layout repeats the final 32 KiB in offsets `0x18000..0x1ffff`.