G4 Mac Mini Audio — Mac OS 9 mute + headphone auto-switch

Real mute and automatic speaker↔headphone switching for the unsupported-G4 Mac Mini (A1103, spoofed as PowerMac5,1) running Mac OS 9.2.2 via the MacOS9Lives hack — packaged as a native Control Strip module. Both are confirmed working on real hardware.

Built on top of matouspikous's "MacMiniAudioFix" amp-enable INIT (MacLegacyLabs), which restores full-volume audio at boot. This project adds the everyday-use pieces that were still missing. See CREDITS.

⚠️ Graduated (slider) volume is not achievable in software on this machine. There's no hardware gain, and the Sound Manager opens its output device and the mixer before any INIT can interpose — so a component wrapper is never called (confirmed on hardware). The only untried avenue is driving the DBDMA buffer directly. Full investigation + open challenge in COMMUNITY-POST.md; pointers welcome.

The hardware problem (short version)

There is no I²C audio codec on this machine (no TAS3004). Volume/amp control is done through GPIO pins in the Intrepid mac-io register block, not codec registers. The screamer driver talks to a codec that isn't there and leaves the output amps disabled — so a stock hack gives near-silent audio. matouspikous's INIT re-enables the amps; this project adds mute and routing on top.

GPIO offset	Role (confirmed by isolation testing)
0x67	Headphone detect — bit 1: 1 = no HP, 0 = HP inserted
0x6F	amp enable → headphone jack
0x70	amp enable → internal speaker
0x6E, 0x79	amp enable — inert on their own

Amp pin states: 0x05 = ON, 0x01 = MUTE (truly silent, incl. the HP jack), 0x04 = standby. Full detail in COMMUNITY-POST.md.

What's in here

init/                 Amp-enable INIT (CodeWarrior source) — the foundation
csm/mini-audio-strip/ The Mini Audio Control Strip module (Retro68 source)
tools/MiniAudioTool/  Interactive GPIO/amp/routing diagnostic app (Retro68 source)
prebuilt/             Ready-to-install binaries — Control Strip module (.bin/.hqx), diagnostic app (.img)
scripts/wrap-apm.py   Wraps a raw HFS image in an Apple Partition Map so OS 9 mounts it
build.sh              Builds the Control Strip module + the diagnostic app

Install (no compiler needed)

1. Amp-enable INIT — keep matouspikous's "MacMiniAudioFix" in System Folder:Extensions: (or build the version in init/ with CodeWarrior). This provides boot audio; everything else depends on it.
2. Control Strip module — decode prebuilt/MiniAudioStrip.hqx (or .bin) on the Mac with StuffIt Expander, copy the resulting MiniAudioStrip into System Folder:Control Strip Modules:, reboot. The tile shows a speaker / headphones / mute icon for the current state, auto-switches on headphone insert, and click to mute/unmute. It's a standard Control Strip module — Option-drag it into or out of the strip like any other.
3. (Optional) diagnostic app — prebuilt/MiniAudioTool.img lets you read GPIO pins and drive the amps by hand. It never touches the boot path.

See prebuilt/README.md for details.

Build from source

The Control Strip module and the diagnostic app build with Retro68 (PowerPC):

RETRO68=$HOME/Retro68-build ./build.sh   # outputs into prebuilt/

The INIT must be built with CodeWarrior on a PowerPC Mac — Retro68 cannot emit a resident PowerPC INIT code resource. Recipe in init/README.md.

Status

• ✅ Real mute — park the amp pins at 0x01 (driven low, no HP-jack leak).
• ✅ Headphone auto-switch — poll 0x67, route 0x6F/0x70. Instant on insert, ~1 s on removal (detect-pin settling, not software).
• ⛔ Graduated volume — not achievable in software here (component layer unreachable from an INIT; only the DBDMA route remains, untried). See the write-up in COMMUNITY-POST.md.

Credits

• Amp-enable foundation & original reverse-engineering: matouspikous (MacLegacyLabs, "MacMiniAudioFix - max sound"). The GPIO and Name Registry code here is reused from that release.
• Mute, pin mapping, auto-switch, Control Strip module: this project.

Licensing: this builds on matouspikous's work — confirm their terms before reuse. A LICENSE file has intentionally not been added yet; see the maintainer.