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DAC and SPU audio

The GPL16250 audio environment contains direct DAC FIFOs and a multi-channel SPU used by resident sound and music resources.

Supported high-level behavior

The SDK and emulator cover:

  • direct PCM FIFO state;
  • SPU PCM8 and PCM16;
  • IMA ADPCM and the recovered ADPCM36 stream;
  • pitch, pan, volume/envelope, looping, and channel completion;
  • SPU beat scheduling used by resident music;
  • IRQ/FIQ routing needed by refill and beat events.

Physical tests have produced audible homebrew PCM, sequences, ADPCM36, and sequenced music. Exact analog characteristics, envelope edge cases, and every ADPCM36 corner remain less certain than digital state transitions.

Output gate

Physical hardware requires the retail-style output-enable sequence in addition to feeding digital samples. Resident APIs and current low-level support own that setup. A port should not reproduce an old four-register snippet unless it also owns the complete audio environment.

Completion semantics

Programmed channel enable and live channel status are different. Natural sample completion clears live status and latches completion events without necessarily erasing the programmed enable mask. This distinction matters to resident state queries and scene progression.

Music heartbeat

Resident M resources use the SPU beat registers and normal interrupt service to advance commands. The emulator schedules the same hardware-visible events even in silent/headless mode. Host audio output is optional; emulated audio state must still advance when it is disabled.

Evidence labels

Digital register/state behavior covered by audio_test is Verified in the emulator. Audible formats exercised on a console are Verified on tested hardware. Exact electrical output and untested codec combinations remain Unknown.