Closes the four gaps named in issue #103 and lands the separable, verified
parts of PR #102. See docs/internal/SPU_FIDELITY_103.md for the per-piece
disposition and the oracle-verification queue.
SPU DSP (issue #103), clean-room from hardware documentation:
- Reverb: the documented 22050 Hz engine — vLIN/vRIN input, same-side and
crossed different-side IIR reflections, 4-tap comb early echo, both
all-pass filters, vLOUT/vROUT output, and the work-area address advance.
Gated on SPUCNT bit 7 for WRITES only; reads, IRQ checks, address advance
and output always run, as on hardware. Addressing is confined to
[mBASE, 0x80000). Per-voice sends from EON, CD send from SPUCNT bits 0+2.
- Noise: 16-bit LFSR with the documented parity feedback, clocked at the
SPUCNT bits 8-13 rate; NON voices substitute it for their ADPCM sample.
- Volume sweeps: all 24 voice L/R plus main L/R. Bit 15 selects sweep vs
direct; sweep is a live envelope on the same rate machinery as ADSR, and a
guest read of a sweeping register returns the live level.
- Capture buffers: CD L/R and voice 1/3 output written to SPU RAM, so a game
that parks the IRQ address there still gets its interrupt.
- SPU IRQ (I_STAT bit 9): checked at every SPU RAM access class — FIFO, DMA
both directions, ADPCM block fetch, capture writes, reverb work-area
accesses — gated on SPUCNT bit 6, mirrored in SPUSTAT bit 6, acked by
clearing SPUCNT bit 6.
The CD-only fast path in spu_render was removed rather than extended: the
SPU now has per-frame work that must run in every path, and an FMV (XA audio
with zero active voices) is exactly the CD-with-reverb case.
This is a clean-room implementation from the psx-spx/nocash register map and
documented algorithm. Beetle's source was deliberately not consulted: it is
GPL-2.0-or-later and this project is PolyForm Noncommercial. PR #16 was
parked for exactly that reason and PR #13's reverb was separately wrong (it
gated on bit 15 of dAPF1, an address offset, instead of SPUCNT bit 7). The
one place this knowingly deviates from hardware is the 22.05 -> 44.1 kHz
reconstruction filter, which the documentation does not specify; it is
isolated in a single function and flagged for oracle comparison.
CAUSE.IP2 (from PR #102):
IP2 is combinational on R3000A — it mirrors the interrupt line and falls the
instant the guest acks I_STAT or masks the source. It was being OR'd in at
delivery and never cleared, in TWO places (the compiled path and
psx_interpreter.c, the latter missed by PR #102), leaving a phantom pending
interrupt that can spin a kernel dispatcher looping on CAUSE.IP & SR.IM.
psx_irq_refresh_cause_ip2() is now the sole writer of bit 10, refreshed at
raise, I_STAT ack, I_MASK write, HLE context restore and power-on. Verified
against the Beetle oracle's irq.cpp/cpu.cpp rather than asserted, and
covered by test_cause_ip2_combinational.
Mid-dispatch audio pump (from PR #102), with a fix: routed through a gate
that mirrors sdl_audio_update's mute/sink decision. Pumping unconditionally
from the VBlank edge, as submitted, would have pushed real audio during every
turbo-load hard mute and defeated the freeze-in-place mute model.
SPU RAM DMA readback (from PR #102): DMA4 in the SPU->RAM direction wrote
literal zeros; SPU RAM is readable memory and titles carry state through it
across an Exec boundary.
Also fixes an unrelated build race found on the way: tools/embed_spirv.py
wrote its intermediate SPIR-V to <source>.spv, so the two runtime targets
that embed the same shaders raced on one path and one deleted the file the
other was reading.
Co-Authored-By: Alexandros Mandravillis <Alexbeav@live.com>
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Matthew Stanley