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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24
crates/gba-core/tests/stop.rs
View file

@ -1,11 +1,11 @@
use gba_core::{
cpu::{Cpu, CpuError, InstructionSet},
cpu::{Cpu, InstructionSet},
display::{CYCLES_PER_FRAME, VBLANK_START},
dma::{DmaError, DMA_BASE},
input::Buttons,
io::{DISPCNT, HALTCNT, IE, IF, IME, KEYCNT, POSTFLG, TIMER_BASE},
machine::{FrameRunError, Machine, MachineError, StepKind},
memory::{Memory, MemoryError, BIOS_SIZE, ROM_START},
memory::{Memory, BIOS_SIZE, ROM_START},
timing::StepTiming,
video::Framebuffer,
};
@ -355,12 +355,12 @@ fn arm_and_thumb_stop_stores_finish_with_normal_cycles_before_freezing() {
}
#[test]
fn failed_block_store_cannot_partially_enter_stop_or_set_postflg() {
fn bios_block_store_enters_stop_and_ignores_the_unused_word_after_haltcnt() {
let mut bios = vec![0; BIOS_SIZE];
bios[..24].copy_from_slice(&words(&[
0xe59f_0008,
0xe59f_1008,
0xe8a0_0006,
0xe8a0_0006, // STMIA r0!,{r1,r2}: POSTFLG=1, HALTCNT=0x80, then unused I/O.
0xeaff_fffe,
POSTFLG,
0x8001,
@ -370,19 +370,11 @@ fn failed_block_store_cannot_partially_enter_stop_or_set_postflg() {
cpu.step(&mut mem).unwrap();
cpu.step(&mut mem).unwrap();
let mut m = Machine::new(cpu, mem);
let before = m.cpu().clone();
assert_eq!(
m.step(),
Err(MachineError::Cpu(CpuError::Memory(MemoryError::Unmapped(
POSTFLG + 4
))))
);
assert_eq!(m.cpu(), &before);
assert!(!m.stopped());
assert_eq!(m.step().unwrap(), StepKind::Instruction);
assert!(m.stopped());
assert!(!m.halted());
assert_eq!(m.memory().read8(POSTFLG).unwrap(), 0);
assert_eq!(m.cycles(), 0);
assert_eq!(m.last_timing(), StepTiming::default());
assert_eq!(m.memory().read8(POSTFLG).unwrap(), 1);
assert_eq!(m.cpu().registers()[0], POSTFLG + 8);
}
#[test]