fix: stabilize desktop audio playback

src/runtime/tests.rs

@@ -1,12 +1,17 @@
 use crate::runtime::{
-    AudioOutput, ClientRuntime, EmulationState, FRAME_RGBA_BYTES, HostConfig, InputProvider,
-    JOYPAD_BUTTON_ORDER, JOYPAD_BUTTONS_COUNT, JoypadButton, NesRuntime, NoopClock,
-    RuntimeHostLoop, VideoMode, VideoOutput, button_pressed, set_button_pressed,
+    button_pressed, set_button_pressed, AudioOutput, ClientRuntime, EmulationState, HostConfig,
+    InputProvider, JoypadButton, NesRuntime, NoopClock, NullAudio, NullInput, NullVideo,
+    RuntimeHostLoop, VideoMode, VideoOutput, FRAME_RGBA_BYTES, JOYPAD_BUTTONS_COUNT,
+    JOYPAD_BUTTON_ORDER,
 };
 use std::cell::Cell;
 use std::rc::Rc;
 
 fn nrom_test_rom() -> Vec<u8> {
+    nrom_test_rom_with_program(&[0xEA, 0x4C, 0x00, 0x80])
+}
+
+fn nrom_test_rom_with_program(program: &[u8]) -> Vec<u8> {
     let mut rom = vec![0u8; 16 + 16 * 1024 + 8 * 1024];
     rom[0..4].copy_from_slice(b"NES\x1A");
     rom[4] = 1; // 16 KiB PRG
@@ -17,11 +22,7 @@ fn nrom_test_rom() -> Vec<u8> {
     rom[reset_vec] = 0x00;
     rom[reset_vec + 1] = 0x80;
 
-    // 0x8000: NOP; JMP $8000
-    rom[prg_offset] = 0xEA;
-    rom[prg_offset + 1] = 0x4C;
-    rom[prg_offset + 2] = 0x00;
-    rom[prg_offset + 3] = 0x80;
+    rom[prg_offset..prg_offset + program.len()].copy_from_slice(program);
     rom
 }
 
@@ -83,6 +84,30 @@ fn audio_mixer_generates_samples() {
     assert_eq!(mixer.sample_rate(), 48_000);
 }
 
+#[test]
+fn audio_mixer_accounts_for_oam_dma_stall_cycles() {
+    let rom = nrom_test_rom_with_program(&[
+        0xA9, 0x00, // LDA #$00
+        0x8D, 0x14, 0x40, // STA $4014
+        0x4C, 0x00, 0x80, // JMP $8000
+    ]);
+    let runtime = NesRuntime::from_rom_bytes(&rom).expect("runtime init");
+    let mode = runtime.video_mode();
+    let mut host = RuntimeHostLoop::with_config(runtime, HostConfig::new(48_000, false));
+
+    let total_samples = host
+        .run_frames_unpaced(120, &mut NullInput, &mut NullVideo, &mut NullAudio)
+        .expect("run frames");
+
+    let expected = ((host.runtime().frame_number() as f64) * 48_000.0 / mode.frame_hz()).round();
+    let drift_pct = ((total_samples as f64 - expected).abs() / expected) * 100.0;
+
+    assert!(
+        drift_pct <= 2.5,
+        "audio drift too high with OAM DMA: {drift_pct:.3}% (samples={total_samples}, expected={expected:.0})"
+    );
+}
+
 struct FixedInput;
 
 impl InputProvider for FixedInput {