RetroArch/android/andretro/assets/libretro_gambatte.so.xml

<retro>
    <system fullname="Nintendo Gameboy" shortname="GB"/>
    <module libraryname="gambatte" extensions="gb|gbc|dmg"/>

    <input>
        <port shortname="p1" fullname="Player 1" defaultdevice="pad">
            <device shortname="pad" fullname="Gamepad">
                <button shortname="up" fullname="Up" mappedkey="UP"/>
                <button shortname="down" fullname="Down" mappedkey="DOWN"/>
                <button shortname="left" fullname="Left" mappedkey="LEFT"/>
                <button shortname="right" fullname="Right" mappedkey="RIGHT"/>
                <button shortname="select" fullname="Select" mappedkey="SELECT"/>
                <button shortname="start" fullname="Start" mappedkey="START"/>
                <button shortname="b" fullname="B" mappedkey="B"/>
                <button shortname="a" fullname="A" mappedkey="A"/>
            </device>
        </port>
    </input>
    
</retro>