SD Card Layout, Bundle Structure, and Launcher Reference

/media/TKGL_BOOTSTRAP/tkgl_bootstrap_DenonPrimeGO/mixxx-bundle/
├── mixxx.real                        # 17 MB binary — DO NOT USE (causes EGLFS crash)
├── bin/
│   └── mixxx -> ../lib/bin/mixxx     # Symlink to working 10 MB binary
├── lib/
│   ├── bin/
│   │   └── mixxx                     # MIXXX 2.5.6 ARMv7 (~10 MB, working binary)
│   ├── libQt5*.so.5                  # Qt 5.15.8 (bundled — device's 5.15.2 not used)
│   ├── libEGL.so -> /usr/lib/libmali.so.14.0   # Mali r1p0 shim
│   ├── libGLESv2.so -> /usr/lib/libmali.so.14.0
│   ├── libasound.so.2                # ALSA
│   ├── libportaudio.so.2             # Audio I/O
│   ├── libFLAC.so.12                 # Codec
│   ├── libmp3lame.so.0               # MP3 codec
│   ├── librubberband.so.2            # Time stretching
│   ├── libkeyfinder.so.2             # Key detection
│   ├── libchromaprint.so.1           # BPM detection
│   └── ...                           # 66+ total shared libraries
├── qt-plugins/
│   ├── platforms/
│   │   └── libqeglfs.so              # EGLFS platform plugin
│   ├── egldeviceintegrations/
│   │   └── libqeglfs-mali-integration.so  # Custom Mali integration (critical)
│   ├── generic/
│   │   └── libqevdevtouchplugin.so   # Touchscreen input
│   ├── imageformats/                 # SVG, ICO support
│   ├── sqldrivers/
│   │   └── libqsqlite.so             # SQLite for MIXXX library DB
│   └── platformthemes/
├── mixxx-mapping/                    # MIDI controller mappings (source reference)
│   ├── Denon-Prime-4*.xml
│   ├── Denon-Prime-4*-scripts.js
│   └── prime-go/
│       ├── Denon-Prime-Go*.xml
│       └── Denon-Prime-Go*-scripts.js
├── mixxx_launcher.sh                 # SD card launcher (env vars + CPU shielding)
├── settings/                         # MIXXX runtime settings
│   ├── mixxx.cfg
│   └── mixxxdb.sqlite                # Library database
├── share/
│   └── mixxx/                        # Resource path (skins, translations)
├── music/                            # USB music library mount point
└── backup/                           # Device binary backup

#!/bin/sh
# MIXXX Launcher — Denon Prime Go / Prime 4 (SD card)
# Auto-detects device model via DRM connector and applies correct display settings.

# Guard against duplicate instances (systemd-run may restart before old process exits)
if pidof mixxx > /dev/null 2>&1; then
    echo "Mixxx already running, exiting."
    exit 0
fi

# Detect device model from DRM connector
# Prime Go  = DSI-1  (rotation 90,  no vsync needed)
# Prime 4   = LVDS-1 (rotation 270, needs SWAPINTERVAL=1)
detect_device() {
    if [ -f /sys/class/drm/card0-DSI-1/status ] && \
       grep -q connected /sys/class/drm/card0-DSI-1/status 2>/dev/null; then
        DEVICE="primego"
        ROTATION=90
        SWAPINTERVAL=0
    else
        DEVICE="prime4"
        ROTATION=270
        SWAPINTERVAL=1
    fi
    echo "[launcher] detected device: $DEVICE (rotation=$ROTATION swapinterval=$SWAPINTERVAL)"
}
detect_device

BUNDLE=/media/TKGL_BOOTSTRAP/tkgl_bootstrap_DenonPrimeGO/mixxx-bundle
MUSIC_DIR="$BUNDLE/music"

# Internal eMMC storage for binaries and libraries (50MHz/8-bit bus vs 25MHz/4-bit SD).
# Loading Qt 5.15.8, Mali integration, and MIXXX binary from fast internal storage
# eliminates MMC bus contention on the external SD during audio playback.
INTERNAL_BUNDLE="/media/az01-internal/mixxx"
if [ -d "$INTERNAL_BUNDLE/lib" ] && [ -f "$INTERNAL_BUNDLE/lib/bin/mixxx" ]; then
    BIN_PATH="$INTERNAL_BUNDLE/bin"
    LIB_PATH="$INTERNAL_BUNDLE/lib"
    PLUGIN_PATH="$INTERNAL_BUNDLE/qt-plugins"
else
    echo "[launcher] internal lib not found, falling back to SD bundle"
    BIN_PATH="$BUNDLE/bin"
    LIB_PATH="$BUNDLE/lib"
    PLUGIN_PATH="$BUNDLE/qt-plugins"
fi

# USB Music Library: mount USB drive to music directory if present
mount_usb_music() {
    [ -d "$MUSIC_DIR" ] || mkdir -p "$MUSIC_DIR"
    mountpoint -q "$MUSIC_DIR" && return 0
    for dev in /dev/sda1 /dev/sdb1; do
        if [ -b "$dev" ]; then
            mount -o ro "$dev" "$MUSIC_DIR" 2>/dev/null && return 0
        fi
    done
    return 1
}
mount_usb_music

# Work around kernel 6.1 hidraw netlink bug — udev's hid_enumerate() hangs without NLMSG_DONE
export LD_PRELOAD=$LIB_PATH/no_hid_poll.so
# Qt 5.15.8 plugins from SD card (NOT device's Qt 5.15.2 — eglfs_emu can't take over fbcon)
export QT_PLUGIN_PATH="$PLUGIN_PATH"
# SD Qt 5.15.8 first, device Qt 5.15.2 fallback, then system libs
export LD_LIBRARY_PATH="$LIB_PATH:/usr/qt/lib:/usr/lib"
export QT_QPA_PLATFORM=eglfs
export QT_QPA_EGLFS_INTEGRATION=eglfs_mali
export QT_QPA_EGLFS_SWAPINTERVAL="$SWAPINTERVAL"
export QT_QPA_EGLFS_ROTATION="$ROTATION"
export QT_QPA_FONTDIR=/usr/share/fonts
export QT_QPA_GENERIC_PLUGINS="evdevtouch:/dev/input/event0 evdevkeyboard:/dev/input/event1"
export QT_QPA_EVDEV_TOUCHSCREEN_PARAMETERS="/dev/input/event0:rotate=$ROTATION:minX=0:maxX=1280:minY=0:maxY=800"
export QT_QPA_EGLFS_PHYSICAL_WIDTH=155
export QT_QPA_EGLFS_PHYSICAL_HEIGHT=98
export HOME=/tmp
export XDG_RUNTIME_DIR=/tmp

# Disable RT throttling — audio threads need 100% of their timeslice.
echo -1 > /proc/sys/kernel/sched_rt_runtime_us

# I/O & VM latency optimizations
for blk in mmcblk0 mmcblk1; do
    echo none > "/sys/block/$blk/queue/scheduler" 2>/dev/null
    echo 512 > "/sys/block/$blk/queue/read_ahead_kb" 2>/dev/null
    echo 64 > "/sys/block/$blk/queue/nr_requests" 2>/dev/null
done
echo 20480 > /proc/sys/vm/dirty_background_bytes 2>/dev/null
echo 1 > /proc/sys/vm/swappiness
echo 200 > /proc/sys/vm/vfs_cache_pressure
echo 10 > /proc/sys/vm/stat_interval
for mp in /data /media/az01-internal /media/TKGL_BOOTSTRAP; do
    mountpoint -q "$mp" 2>/dev/null && mount -o remount,noatime,nodiratime,commit=60 "$mp" 2>/dev/null
done

# Launch MIXXX pinned to CPU cores 2-3 (audio-dedicated cores).
# We do NOT set RT priority on the main process — that would cause ALL
# 44+ child threads to inherit SCHED_FIFO and compete with audio.
taskset -c 2,3 $BIN_PATH/mixxx -platform eglfs --settingsPath $BUNDLE/settings --resourcePath $BUNDLE "$@" &
MIXPID=$!

# Post-launch: selectively boost audio-critical threads, banish everything else
BANISH_PATTERNS="mali-|CachingReader|QEvdevTouch|StatsManager|QDBus|VinylControl|LibraryScanner|BrowseThread|AnalyzerThread|Controller$|VSync|gmain|gdbus|Thread \(pooled\)|QQuickPixmapRea|QQmlThread|libusb_event"

for i in $(seq 1 12); do
    sleep 1
    for tid in $(ls /proc/$MIXPID/task/ 2>/dev/null); do
        name=$(cat /proc/$MIXPID/task/$tid/comm 2>/dev/null)
        case "$name" in
            EngineWorkerSch|EngineSideChain)
                chrt -f -p 98 $tid 2>/dev/null
                taskset -p 0x0C $tid 2>/dev/null
                ;;
        esac
        if echo "$name" | grep -qE "$BANISH_PATTERNS"; then
            chrt -o -p 0 $tid 2>/dev/null
            taskset -p 0x03 $tid 2>/dev/null
        fi
    done
done
# Pin main process to non-audio cores 0-1 at SCHED_OTHER so newly-spawned
# threads (e.g. Qt thread pool) inherit non-audio affinity by default.
chrt -o -p 0 $MIXPID 2>/dev/null
taskset -p 0x03 $MIXPID 2>/dev/null

wait $MIXPID

sqlite3 /media/TKGL_BOOTSTRAP/tkgl_bootstrap_DenonPrimeGO/mixxx-bundle/settings/mixxxdb.sqlite \
  "SELECT directory FROM directories;"

sqlite3 /media/TKGL_BOOTSTRAP/tkgl_bootstrap_DenonPrimeGO/mixxx-bundle/settings/mixxxdb.sqlite \
  "INSERT INTO directories (id, directory, volume) VALUES (1, '/media/TKGL_BOOTSTRAP/tkgl_bootstrap_DenonPrimeGO/mixxx-bundle/music', 1);"

[Config]
FirstRun=1
HasScreenedForLibraryDir=1

[Library]
Directory[0]=/media/TKGL_BOOTSTRAP/tkgl_bootstrap_DenonPrimeGO/mixxx-bundle/music
RescanOnStartup=0