0xrsydn/gameboy-rust
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fix(memory): ignore CPU and DMA writes to unused I/O addresses

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Stores to I/O addresses with no register returned Unmapped and stopped the
machine. Hardware ignores them. Emulated writes there now pay their bus cost and
change nothing; host writes stay strict. The unmodeled internal memory control
register at 0x04xx0800 and all unused I/O reads remain diagnostics.

Rollback tests that used unused I/O as their failing word now run the block on
to a register that rejects the stored value: SIOMULTI2 outside multiplayer
mode, an RCNT GPIO serial IRQ, or 64-sample wave playback. Where no reachable
register can fail (JOYSTAT, POSTFLG/HALTCNT, IME, DMA3CNT), the test now checks
that the block commits and the unused word is ignored.

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 11:38:51 +07:00
commit 20176716d9
16 changed files with 166 additions and 92 deletions
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49
crates/gba-core/tests/machine.rs
View file

@ -194,7 +194,7 @@ fn diagnostics_do_not_advance_timers_or_clock() {
#[test]
fn late_block_store_error_does_not_change_timer_reload_or_enable() {
let mut machine = prepared(
0xe8a0_003e,
0xe8a0_07fe,
&[
(0, TIMER_BASE),
(1, 0x00c0_ffff),
@ -203,7 +203,7 @@ fn late_block_store_error_does_not_change_timer_reload_or_enable() {
(4, 0x00c0_ffff),
(5, 123),
],
); // STMIA r0!, {r1-r5}; fifth word is unmapped
); // STMIA r0!, {r1-r10}; unused words are ignored, and r10 reaches SIOMULTI2
let before = machine.cpu().clone();
assert!(machine.step().is_err());
assert_eq!(machine.cpu(), &before);
@ -217,23 +217,19 @@ fn late_block_store_error_does_not_change_timer_reload_or_enable() {
}
#[test]
fn late_block_store_error_does_not_acknowledge_if_or_modify_ie() {
fn block_store_over_ime_padding_commits_ie_if_waitcnt_and_ime() {
let mut machine = prepared(
0xe8a0_001e,
&[(0, IE), (1, 0x0008_ffff), (2, 123), (3, 1), (4, 42)],
);
// IE/IF, WAITCNT, IME are valid. The fourth word at 0x0400020c is not.
// IE/IF, WAITCNT, and IME are written. The fourth word at 0x0400020c is unused.
pending_timer(machine.memory_mut());
machine.memory_mut().write32(IME, 0).unwrap(); // Let the invalid store execute
let before = machine.cpu().clone();
let cycles = machine.cycles();
assert!(machine.step().is_err());
assert_eq!(machine.cpu(), &before);
assert_eq!(machine.cycles(), cycles);
assert_eq!(machine.memory().read32(IE).unwrap(), 0x0008_0008);
assert_eq!(machine.memory().read32(WAITCNT).unwrap(), 0);
assert_eq!(machine.memory().read32(IME).unwrap(), 0);
assert_eq!(machine.last_timing().total(), 0);
machine.memory_mut().write32(IME, 0).unwrap(); // Let the store execute
assert_eq!(machine.step().unwrap(), StepKind::Instruction);
assert_eq!(machine.cpu().registers()[0], IE + 16);
assert_eq!(machine.memory().read32(IE).unwrap(), 0x3fff); // IF bit 3 acknowledged.
assert_eq!(machine.memory().read32(WAITCNT).unwrap(), 123);
assert_eq!(machine.memory().read32(IME).unwrap(), 1);
}
#[test]
@ -271,3 +267,28 @@ fn cpu_only_step_does_not_advance_device_time_or_deliver_irq() {
assert_eq!(bus.cycles(), cycles);
assert!(bus.irq_pending());
}
#[test]
fn cpu_stores_to_unused_io_are_ignored_but_memory_control_and_host_writes_stay_strict() {
for address in [
0x0400_0058,
0x0400_00e0,
0x0400_020c,
0x0400_0304,
0x0401_0100,
] {
let mut machine = prepared(0xe580_1000, &[(0, address), (1, u32::MAX)]); // STR r1,[r0]
assert_eq!(machine.step().unwrap(), StepKind::Instruction);
assert_eq!(
machine.memory_mut().write32(address, 0),
Err(MemoryError::Unmapped(address))
);
}
let mut machine = prepared(0xe580_1000, &[(0, 0x0400_0800), (1, 0)]);
let before = machine.cpu().clone();
assert_eq!(
machine.step(),
Err(MachineError::Cpu(MemoryError::Unmapped(0x0400_0800).into()))
);
assert_eq!(machine.cpu(), &before);
}