Crate rustynes_apu 

Cycle-accurate Ricoh 2A03 APU implementation.

See docs/apu-2a03.md for the implementation spec and ref-docs/research-report.md §APU for the source material.

Five-channel APU (pulse 1, pulse 2, triangle, noise, DMC) with the lookup-table non-linear mixer, analog highpass / lowpass filter chain, frame counter (4-step + 5-step modes with the documented IRQ flag), band-limited synthesis at host sample rate, and DMC sample DMA. The bus-side DMC DMA scheduling lives in rustynes-core::LockstepBus.

Modules

provenance

Audio provenance (v2.3.7 “Overtone”) — why does this moment sound like that?

Structs

Apu

Top-level APU.

BlipBuf

Streaming BLEP decimator + filter chain that feeds host-rate samples to the frontend’s audio thread.

Dmc

DMC channel state.

Envelope

Envelope generator.

FilterChain

3-stage filter chain. The stages are model-dependent (see FilterModel); the default FilterModel::NesRf is HPF 90 Hz → HPF 440 Hz → LPF 14 kHz.

FrameCounter

Frame counter state.

FrameEvents

Output of one APU tick describing what events the frame counter fired.

LengthCounter

Length counter shared by pulse, triangle, noise channels.

Mixer

Pre-computed mixer state.

Noise

Noise channel state.

OnePole

Single-pole IIR filter. lpf flag controls whether it’s a low-pass or high-pass.

Opll

OPLL (YM2413 / VRC7) FM synthesizer instance.

OpllPatch

One OPLL patch — the 13-field instrument definition.

Pulse

Pulse channel state.

Triangle

Triangle channel state.

Enums

ApuSnapshotError

Errors returned by Apu::restore.

FilterModel

v2.1.3 — the analog output-filter model the APU emulates.

FrameCounterMode

Frame counter mode.

OpllChipType

Chip type — selects the patch ROM table.

OpllStateError

Errors returned by Opll::restore.

Region

NES region — picks clock dividers and per-region tables.

Constants

APU_SNAPSHOT_VERSION

Schema version for the APU snapshot blob.

CHANNEL_GAIN_UNITY

All Apu::channel_gain entries at 1.0 — every channel at full, unattenuated output (the default and the byte-identical value the oracle / test ROMs always run with).

CHANNEL_MASK_ALL

All Apu::channel_mask bits set — every channel audible (the default and the determinism-safe value the oracle / test ROMs always run with).

CPU_HZ_NTSC

CPU cycles per second, NTSC.

CPU_HZ_PAL

CPU cycles per second, PAL (slightly slower).

LENGTH_TABLE

32-entry length lookup table (from the NESdev wiki).

NTSC_NOISE_PERIODS

16-entry NTSC noise period table (NESdev wiki). Index = bits 0-3 of $400E.

OPLL_SNAPSHOT_LEN

Total serialized size of an OPLL snapshot, in bytes.

OPLL_SNAPSHOT_VERSION

Schema version of the blob Opll::snapshot emits.

PAL_NOISE_PERIODS

16-entry PAL noise period table (NESdev wiki).

Statics

REENABLE_BUMP

v2.0 Phase 2 (mc-r1-dmc-reenable-phase): swept byte-timer realignment.

SUBPOS_DELAY

v2.0 final lever #1 (mc-r1-dmc-halt-subpos): swept per-CPU-cycle arm DELAY.

Traits

ApuBus

Bus surface seen by the APU. A small subset of the full CPU bus for the DMC’s sample-fetch DMA.

Functions

version

Returns the crate version string.