Pi Settings

The Adafruit Stereo Bonnet uses two MAX98357A I2S amplifier chips (one per channel). The Linux kernel includes the max98357a device tree overlay, and Batocera's kernel image includes the max98357a.dtbo file, so no driver compilation is needed.

Step 1: SSH

From a terminal, ssh into the Raspberry Pi:

ssh  [email protected]

Default password is linux. If the hostname doesn't resolve, use the Pi's IP address.

Step 2: Remount /boot as Writeable

By default /boot is read-only. Remount it writable for this session:

mount -o remount,rw /boot


Verify it worked:

echo $?

Should return 0. Note: /boot returns to read-only after each reboot, but file edits written to the vfat partition persist permanently.

Step 3: Confirm Overlay

ls /boot/overlays/ | grep max


You should see max98357a.dtbo in the output. 

Step 4: Add the Device Tree Overlay to config.txt

echo "" >> /boot/config.txt
echo "# Adafruit Stereo Bonnet" >> /boot/config.txt
echo "dtparam=i2s=on" >> /boot/config.txt
echo "dtoverlay=max98357a" >> /boot/config.txt

Verify the lines were appended correctly:

tail -5 /boot/config.txt

You should see:

Adafruit Stereo Bonnet
dtparam=i2s=on
dtoverlay=max98357a

Step 5: Set the Audio Device in batocera.conf

echo "audio.device=hw:MAX98357A" >> /userdata/system/batocera.conf

Step 6: Reboot the Pi

reboot

Step 7: Verify the Card is Detected

After the Pi restarts, ssh back in and run:

aplay -l

You should see output like:

card 0: MAX98357A [MAX98357A], device 0: 1f000a0000.i2s-HiFi HiFi-0 [...]

HDMI audio cards (vc4hdmi0, vc4hdmi1) will also appear — that's normal.

Step 8: Test Audio Output

Plug in your speakers, then play white noise to confirm the speakers are working:

aplay -D hw:MAX98357A -r 44100 -f S16_LE -c 2 /dev/urandom

You should hear static from both speakers. Press ctrl+c to stop.

Step 9: Set Audio Output in Batocera UI

(We'll do this step later when the full machine is built, but I put it here just for completeness or in case you have temporary controls and monitor hooked up)

1. In EmulationStation press the START button to open the main menu
2. Go to System Settings > Audio Output > Built-In Audio Stereo
3. Got to System Settings > Audio Profile > MAX98357A Stereo Output

This ensures EmulationStation and all emulators route audio to the Stereo Speaker Bonnet.

Troubleshooting Audio

aplay -l doesn't show MAX98357A after reboot

• Confirm the overlay lines are at the bottom of /boot/config.txt with tail -5 /boot/config.txt
• Confirm max98357a.dtbo exists in /boot/overlays/
• Make sure the bonnet is fully seated on the GPIO header

No sound from speakers

• Confirm audio.device=hw:MAX98357A is in /userdata/system/batocera.conf
• Check the EmulationStation audio settings and confirm MAX98357A is selected
• Check ALSA volume: amixer -c MAX98357A — if Master is at 0, set it with amixer -c MAX98357A sset Master 90%

/boot is read-only when trying to edit

• Run mount -o remount,rw /boot before editing — this is required after every reboot

Additional Notes

• /boot remounts read-only after every reboot but file changes persist on the vfat partition
• batocera.conf and all files under /userdata survive Batocera system updates
• The MAX98357A has no hardware volume register — volume is controlled via ALSA software mixing