ZZ9000AX AHI audio emulation

Amiberry’s ZZ9000 board model also exposes the AX audio registers and the legacy TX and RX rings. A real-system zz9000ax.audio subdriver uses the same ConfigDev and register protocol in Amiberry as it does with the card. The driver does not need an emulator build or an installation change.

Implemented interface

The card window begins at the Zorro board address. Register accesses occupy the first 64 KiB. Card memory begins at board offset 0x10000. The legacy audio TX and RX rings are at board offsets card_size - 0x10000 and card_size - 0x8000 respectively. Each holds eight 3840-byte periods.

Offset	Meaning
0x04	Read pending interrupt flags (Ethernet = bit 0, audio = bit 1); write bits 3 and 5 to acknowledge audio
0x70	Write a TX period offset divided by 256 to convert the guest’s BE samples; read the last collision flag
0x74	Audio frames per 20 ms period; playback and capture run at frames × 50 Hz
0xF4	Read AX presence and TX status capability (0x0003); write playback and capture interrupt enables
0xF6	Packed RX completed period and sequence
0xF8	Packed TX completed period and sequence

The status words have bit 15 set, the completed period in bits 12–14, and a 12-bit sequence in bits 0–11. 0xE6 still reads zero, keeping the installed driver on its legacy aperture and register path.

The emulator advances the formatter at a host-time 20 ms cadence during emulation. TX slots contain guest big-endian stereo S16 samples; the 0x70 kick swaps the submitted period and SDL plays it at the guest’s selected rate. Capture converts host little-endian stereo S16 into the guest’s big-endian RX ring. Missing host capture data becomes silence while period status continues to advance. Selecting no sampler keeps the host microphone closed and supplies silence to the RX ring. Playback follows the Master and AHI volume controls, mute, and AHI channel-swap preference; capture follows the same channel-swap preference. Libretro does not expose AX audio yet because its SDL audio stream stub does not forward samples to the frontend.

All card memory, register, status, and interrupt updates run from the emulation callback. A completed period asserts Paula’s INTB_EXTER request (bit 13, level 6) by default. The stock driver’s interrupt server reads 0x04, acknowledges audio without clearing Ethernet, and wakes its AHI worker. The card model clears audio pending on acknowledgement, stop, and reset. Ethernet and audio share the selected Paula line; a source that remains pending is asserted again after Exec services the other source. Set zz9000_int2=true when the guest has ENV:ZZ9K_INT2 so both installed drivers use INTB_PORTS (bit 3, level 2).

Validation

Build Amiberry, then boot a ZZ9000 system drive using a configuration with a ZZ9000 board. Start an AHI application that selects ZZ9000AX. Useful Amiberry.log milestones are:

1. ZZ9000AX: probed — the installed subdriver found the AX card.
2. ZZ9000AX: intreq mask — playback or capture started.
3. ZZ9000AX: audio interrupt pending followed by interrupt acked — the installed ISR serviced a completed period.
4. Repeated period lines with advancing TX sequence and nonzero peak while playing audible content — the worker is refilling the ring.

Playback was verified with a real A4000 system image and its installed AHI subdriver: the guest booted, audio was heard, interrupt acknowledgements and SWAB kicks continued, and the TX sequence advanced beyond 1,250 with nonzero sample peaks. Capture has not been tested. The emulator currently models the legacy AHI register path, without the SDK audio fabric or DSP parameter operations.