0xrsydn/gameboy-rust
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feat(memory): support ARM unused-memory open-bus reads

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Snapshot mapped PC+8 bytes for ARM data reads in the documented unused ranges. Preserve strict host/fetch/Thumb/DMA diagnostics, missing-ROM errors, existing write rules, and nominal timing. Add original regressions and document the bounded model.

The unmodified pinned jsmolka ARM ROM now reaches its verified checkpoint with r12=0 in debug and release: 1344 steps and 11257 nominal cycles. No ROM, manifest, or assertion changes.

Validated on Darwin arm64: 842 workspace tests in debug and release; 773 core/demo tests separately; Python adapter tests; native ROM windows; all ten demo window smoke tests; fmt, clippy, and rustdoc.
This commit is contained in:
0xrsydn 2026-10-05 20:25:18 +07:00
commit a9493d4cc6
11 changed files with 418 additions and 26 deletions
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4
crates/gba-core/src/cpu.rs
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@ -22,6 +22,8 @@ mod instruction_tests;
#[cfg(test)]
mod load_alias_tests;
#[cfg(test)]
mod open_bus_tests;
#[cfg(test)]
mod status_tests;
#[cfg(test)]
mod tests;
@ -200,7 +202,7 @@ impl Cpu {
fn execute_fetched(&mut self, instruction: u32, memory: &mut Memory) -> Result<(), CpuError> {
// Record the executing instruction, not an operand's pipelined PC value.
// Always clear the access context, including on diagnostic errors.
memory.begin_cpu_access(self.pc());
memory.begin_cpu_access(self.pc(), self.instruction_set);
let result = self.execute_instruction(instruction, memory);
memory.end_cpu_access();
result