0xrsydn/gameboy-rust
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fix(memory): ignore CPU and DMA writes to the Game Pak ROM windows

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Stores to 0x08-0x0c returned ReadOnly and stopped the machine. Hardware ignores
them, and a second game's boot code stores to a ROM mirror. Emulated writes now
pay their bus cost and change nothing. The 0x0d window stays a diagnostic until
EEPROM is modeled there, and host writes stay strict.

Tests that used a ROM store as their failing write now cross an ignored ROM
word into the 0x0d window.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HhfHfHEuzv2AUTd6erW1gU
This commit is contained in:
0xrsydn 2026-10-14 08:26:03 +07:00
commit 258fbff2fa
25 changed files with 86 additions and 74 deletions
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10
crates/gba-core/tests/bios/differential.rs
View file

@ -321,17 +321,13 @@ fn failed_source_reads_keep_completed_units_but_not_pending_halfwords() {
}
#[test]
fn destination_failure_preserves_preceding_completed_halfword() {
fn destination_failure_follows_an_ignored_rom_halfword() {
for service in [0x17, 0x18] {
let (data, _) = filtered(service, &[0x12, 0x34, 0x56, 0x78]);
let (mut m, _) = prepare(service, false, 0x07ff_fffe, &data);
let (mut m, _) = prepare(service, false, 0x0cff_fffe, &data);
assert_eq!(
fail(&mut m),
MachineError::Cpu(MemoryError::ReadOnly(ROM_START).into())
);
assert_eq!(
m.memory().read16(0x07ff_fffe).unwrap(),
if service == 0x17 { 0x3412 } else { 0x12 }
MachineError::Cpu(MemoryError::ReadOnly(0x0d00_0000).into())
);
}
}