The read stream froze read_delay whenever the guest had an unacked
controller INT (and while the sector buffer was undrained). Real drives
never pause: measured on MMX4's attract/title XA music, the freeze
accumulated ~1M guest cycles/second (~3% of disc time), every XA sector
arrived 32-92 samples late, and the XA->SPU cd_ring starved ~147 samples
5-6x per second — audible as a 6 Hz crackle/dropout flutter in all
XA-streamed music (user report: MMX4 Zero ice-stage attract demo).
Faithful model, mirrored from the in-tree Beetle oracle (cdc.cpp
HandleSectorRead / SetAIP / CheckAIP / ClearAIP):
- Disc time NEVER pauses while reading; sectors are read on exact
cycle schedule. XA-ADPCM realtime audio flows to the SPU decoder
unconditionally (this alone removes the crackle).
- A data sector that comes due while the guest still has an unacked
INT overwrites the sector buffer on schedule (hardware clobbers its
FIFO the same way) and its data-ready INT1 pends ONE deep, presented
the moment the guest fully acks (Beetle CheckAIP). A newer sector
replacing an unpresented notification is counted + traced 'P'
(Beetle "Previous notification skipped").
- Drive-state changes (Read/Play/Pause/Stop/Seek paths through
start/stop_read_stream) cancel the pended notification (ClearAIP).
- The active-DMA refill path (deliver without new INT while a
multi-sector CD DMA drains) is unchanged.
Verification on MMX4 (SLUS-00561) title/attract XA:
- CD_PUSH guest-cycle spacing: exactly 1,806,336 cycles (8 sectors at
2x), min == max over 148 pushes (was 1.83-1.88M, systematically late).
- read_hold_cycles == 0 (was ~30.8M per 30 s) — kept as an always-on
regression tripwire in cdrom_state.
- int1_pended == 0 during music: X4 acks fast; the pending path only
arms for genuinely slow acks.
- spu_out/host tap rings: 6 Hz zero-gap storm (86-144 gaps/95 s of
147-265 samples) eliminated; only real content silences remain.
- cd_underflow_frames stays 0 during playback.
Always-on observability added (ring-buffer doctrine):
- XA zero-run scanner in the decode path -> AUDIO_EV_XA_ZERO events
(stage 0 = post-ADPCM, stage 1 = post-resample+volume, with LBA).
- CD_PUSH audio events now stamp the global guest-cycle clock (the
spu_out sample stamp is pump-quantized and cannot measure cadence).
- cdrom_state: read_hold_cycles/read_hold_events (must stay 0),
int1_pended / int1_lost / int1_pending_now.
- Savestate: pending_dataready fields appended to CDROM_SNAP_FIELDS.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Two hardware-faithfulness fixes found by the always-on tap rings + Beetle
oracle A/B on fingerprint-matched attract music (tools/audio_pair_segments):
the recomp played the identical track at -3.8 dBFS vs the oracle's
-14.1 dBFS — +10.3 dB hot, clipping continuously.
1. spu.c: the voice repeat/loop address register (voice reg 7) is LIVE
state on real hardware — writing it after KEYON retargets where the
next END+REPEAT block jumps (Beetle spu.cpp:1150/333), and the block
auto-latch (flag bit 2) updates the guest-visible register (386/1302).
The recomp cached repeat_addr at KEYON only, so X5's driver idiom —
KEYON, then point the loop register at a silent tail block; no KEYOFF
ever — left voices looping the LOUD sample body forever. Measured: 3
stuck voices re-looping ~1400x/s, 160k SPU events/min vs the oracle's
633, zero game KEYOFF writes (the game never needs one), +11 dB.
2. cdrom.c: implement the CD controller's decode volume matrix
([src][port], 0x80 unity, pending banks + apply latch at 1F801803.3
bit 5 — mapping copied from Beetle cdc.cpp:1483-1501, applied after
the XA resample per PS1 hardware tests). X5 drives it constantly:
0x73-0x7E steady, ramped to 0x00 at scene changes (measured via the
new beetle `cdc_volume` command + PS_CDC::PSXRecomp_GetDecodeVolume
peek). Without it music fades never happened and steady level sat
~0.6 dB hot.
Also: AUDIO_TAP_VOICES (T0 voice-sum tap) for source-by-source mix
decomposition, per-tap WAV rates, bridge stats in audio_stats.
Measured after (MMX5 attract, 20-25 s windows):
spu_out RMS: -3.8 dBFS (clipping) -> -15.5 dBFS [oracle -14.1]
music-only chain already matched the oracle at -14.8 dBFS, confirming
decoder + mixer gain equivalence; the entire excess was stuck voices.
underruns: 2 events / 98 s (delivery fix holding).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Replace the push-model SDL_QueueAudio output with the shared band-limited
polyphase resampler + P-only fill servo (recomp_audio_drc.h), fed by an SPSC
ring under SDL_LockAudioDevice and drained by a pull callback. The SPU renders
44100/60 per wall-clock frame while the host consumes on its own crystal; the
unsynchronized clocks drifted the queue to underrun (silence gaps = sustained
crackle). The bridge nudges the resample ratio <=+/-0.5% to hold the ring near
target so the queue never runs dry.
Measured on MMX6: legacy push ~1.5-2.5 underruns/s (queue draining to 0ms) ->
bridge 0 underruns, fill held ~50ms. PSXRECOMP_AUDIO_LEGACY=1 keeps the old
push path for A/B; PSXRECOMP_AUDIO_PROBE=1 prints the fill/underrun trend.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Measurement infrastructure for the audio-quality campaign (MMX5 complaint),
ported from snesrecomp's audio_trace/oracle methodology and the
_audio_round2 tap model. No behavior change to the audio path itself.
- audio_trace.{c,h}: three always-on 95 s PCM rings — T1 spu_out (canonical
spu_render output), T2 cd_in (XA/CD-DA PCM entering the SPU CD bus),
T3 host (exact post-fade bytes handed to SDL_QueueAudio) — plus a 512k
event ring (every SPU reg write stamped with the SPU sample clock;
RENDER/PUMP_SKIP/UNDERRUN/MUTE/UNMUTE/CD_PUSH/SPU-DMA), audible-vs-
silent counters (-42 dBFS gate), queue watermarks, and a server-side
44100 Hz WAV dumper (rate exactness matters: snesrecomp da33c06).
- psx-beetle: the libretro audio callbacks stop discarding Beetle's fully-
mixed reference SPU PCM and record it into the same tap ring. Port 4380
gains audio_stats/audio_wav/audio_events with the identical wire protocol
as the runtime (rule 16 symmetric harness) — the oracle WAV capture.
- debug_server: audio_stats / audio_wav / audio_events on the runtime port.
- tools: audio_ab_diff.py + audio_spectral_ab.py (drift-tolerant offline
A/B: drift ppm, onsets, cents, timbre, click rate) and audio_analyze.py
(first-dirty-tap cross-tap decision tree) ported from snesrecomp/
_audio_round2; audio_capture_ab.py dumps both processes symmetrically.
Probes query history; nothing is armed at probe time.
Matthew Stanley