ym2149-ay-replayer – ZXAY/EMUL player with Z80 emulation

Cycle-accurate Project AY (.ay) playback for Rust. This crate parses the original ZXAY/EMUL container, reconstructs the signed pointer-based structures (header, subsongs, points, block tables) and runs the embedded Z80 player inside a pure Rust environment powered by iz80 and the workspace’s ym2149 chip.

Project AY delivered thousands of Spectrum and CPC rips that bundle a tiny Z80 replay as part of the file. Instead of shipping bespoke shims, this crate emulates that player verbatim – including the Motorola-endian headers, signed block offsets, and port wiring for ZX/CPC machines.

Highlights

• 🧾 ZXAY parser – validates header signatures, extracts metadata, subsongs, NT strings, and memory block layouts.
• 🧠 Z80 execution – runs the bundled player using the iz80 core, including INIT/INTERRUPT entries, stack setup, register presets, and per-frame interrupts.
• 🎹 Real PSG bridge – wired to the shared ym2149 backend so the CLI, Bevy plugin, exporter, and wasm builds all hear the same output.
• 🕹 CPC + Spectrum – detects PPI-style port access (#F4xx/#F6xx) and re-tunes the PSG clock for 1 MHz CPC rips while keeping 2 MHz for ZX files.
• 📦 ProjectAY fixtures – unit tests load real songs (SpaceMadness.AY, impact demo 3_2.ay) to guard against parser or emulator regressions.
• 🔌 Reusable player – AyPlayer implements the same RealtimeChip/PlaybackController traits as the YM and Arkos players, so downstream code just boxes one more variant.

Quick Start

[dependencies]
ym2149-ay-replayer = "0.7"
# Optional but common when you plan to pipe the samples into the rest of the stack
ym2149 = "0.7"

use ym2149_ay_replayer::{load_ay, AyPlayer};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let data = std::fs::read("ProjectAY/Spectrum/Demos/SpaceMadness.AY")?;
    let ay = load_ay(&data)?;
    println!("File version: {}", ay.header.file_version);
    println!("Songs: {}", ay.songs.len());

    let (mut player, meta) = AyPlayer::load_from_bytes(&data, ay.header.first_song_index as usize)?;
    println!("Playing: {}", meta.song_name);

    player.play()?;
    let samples = player.generate_samples(882); // ≈ one 50 Hz frame @ 44.1 kHz
    println!("Rendered {} samples", samples.len());
    Ok(())
}

Firmware Limitations

The player only handles AY drivers that run entirely out of their own code/data; once a track calls into the Spectrum or CPC ROM jump table we stop playback and report that firmware emulation is unsupported. ZX files that stay self-contained work fine; CPC AY rips and ROM-heavy ZX rips should be played in a full emulator instead.

When to use it

• Integrate .ay playback into tooling alongside .ym and .aks files
• Feed AY songs through the CLI (ym2149-replayer-cli), Bevy plugin, or wasm demo without branching per format
• Inspect AY headers / block layouts when writing conversion pipelines

API Surface

• load_ay → low-level parser returning AyFile (header metadata, song list, block descriptors)
• AyPlayer → Z80 + PSG player with familiar play/pause/stop/generate_samples methods
• AyMetadata → descriptive info for UIs/inspectors
• AyMachine → host implementation of the AY memory map + PSG port bridging

The player mirrors the workspace conventions: it is Send, implements PlaybackController, exposes mute toggles, register snapshots, and playback position helpers.

Relationship to the Workspace

• CLI (ym2149-replayer-cli): file detection now routes .ym, .aks, and .ay to the correct player, reusing the same streaming
  • visualization stack.
• Bevy (bevy_ym2149): YmSongPlayer gained an Ay variant so assets dropped into Bevy can be YM/AKS/AY without code changes.
• WASM (ym2149-wasm): browser player auto-detects AY files and uses the same AyPlayer under the hood.
• Docs/Examples: Project AY fixtures live in /ProjectAY/ and are used by both tests and the stats helper in examples/stats.rs.

Testing

# Parser + player tests (uses bundled AY fixtures)
cargo test -p ym2149-ay-replayer

# Optional helper to scan fixture stats (interrupt usage, etc.)
cargo run -p ym2149-ay-replayer --example stats -- ProjectAY

The fixtures cover both Spectrum and CPC titles so we don’t regress on port wiring, pointer arithmetic, or INIT/INTERRUPT fallbacks.

Have more AY test material? Drop it under ProjectAY/ and extend the unit tests – the more demoscene rips we cover, the safer future refactors become. Questions/bugs? Open an issue on the main repo. Happy tuning!

CPC Firmware Notes

Some .ay files target the Amstrad CPC firmware: they talk to the PSG via the PPI (#F4xx/#F6xx) and rely on jump tables, AMSDOS buffers, and keyboard handlers that live in the CPC ROM/RAM workspace. Emulating that environment correctly requires bundling the original ROMs and a sizable portion of the CPC OS, which is well beyond the scope of this crate (and comes with legal/licencing uncertainties). As a result CPC-based AY files are currently not supported: the player will detect the CPC port traffic, stop playback, and report that firmware emulation is missing.

ZX Spectrum AY rips continue to work normally; if you need CPC playback, use a full CPC emulator or a specialised player that ships the firmware.