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Commit a40880a4 authored by Robert Wu's avatar Robert Wu
Browse files

BluetoothMidiService: Subtract header from MTU 

In Android 14, the Bluetooth team changed how they handle MTU.
BluetoothMidiService should now subtract 5 from the MTU.

Bug: 308909343
Test: CTS Verifier Bluetooth MIDI tests
Change-Id: Ie6f36fc5baa0563ab3bf7600de404fe9b8eb0434
parent 0edd8471

media/packages/BluetoothMidiService/src/com/android/bluetoothmidiservice/BluetoothMidiDevice.java

+21 −6
Original line number Diff line number Diff line
@@ -50,8 +50,16 @@ public final class BluetoothMidiDevice { 
    private static final String TAG = "BluetoothMidiDevice";

    private static final boolean DEBUG = false;



    private static final int DEFAULT_PACKET_SIZE = 20;

    private static final int MAX_PACKET_SIZE = 512;

    // Bluetooth services should subtract 5 bytes from the MTU for headers.

    private static final int HEADER_SIZE = 5;

    // Min MTU size for BLE

    private static final int MIN_L2CAP_MTU = 23;

    // 23 (min L2CAP MTU) - 5 (header size)

    private static final int DEFAULT_PACKET_SIZE = MIN_L2CAP_MTU - HEADER_SIZE;

    // Max MTU size on Android

    private static final int MAX_ANDROID_MTU = 517;

    // 517 (max Android MTU) - 5 (header size)

    private static final int MAX_PACKET_SIZE = MAX_ANDROID_MTU - HEADER_SIZE;



    //  Bluetooth MIDI Gatt service UUID

    private static final UUID MIDI_SERVICE = UUID.fromString(
@@ -135,8 +143,8 @@ public final class BluetoothMidiDevice { 
                        // switch to receiving notifications

                        mBluetoothGatt.readCharacteristic(characteristic);



                        // Request higher MTU size

                        if (!gatt.requestMtu(MAX_PACKET_SIZE)) {

                        // Request max MTU size

                        if (!gatt.requestMtu(MAX_ANDROID_MTU)) {

                            Log.e(TAG, "request mtu failed");

                            mPacketEncoder.setMaxPacketSize(DEFAULT_PACKET_SIZE);

                            mPacketDecoder.setMaxPacketSize(DEFAULT_PACKET_SIZE);
@@ -204,8 +212,15 @@ public final class BluetoothMidiDevice { 
        public void onMtuChanged(BluetoothGatt gatt, int mtu, int status) {

            Log.d(TAG, "onMtuChanged callback received. mtu: " + mtu + ", status: " + status);

            if (status == BluetoothGatt.GATT_SUCCESS) {

                mPacketEncoder.setMaxPacketSize(Math.min(mtu, MAX_PACKET_SIZE));

                mPacketDecoder.setMaxPacketSize(Math.min(mtu, MAX_PACKET_SIZE));

                int packetSize = Math.min(mtu - HEADER_SIZE, MAX_PACKET_SIZE);

                if (packetSize <= 0) {

                    Log.e(TAG, "onMtuChanged non-positive packet size: " + packetSize);

                    packetSize = DEFAULT_PACKET_SIZE;

                } else if (packetSize < DEFAULT_PACKET_SIZE) {

                    Log.w(TAG, "onMtuChanged small packet size: " + packetSize);

                }

                mPacketEncoder.setMaxPacketSize(packetSize);

                mPacketDecoder.setMaxPacketSize(packetSize);

            } else {

                mPacketEncoder.setMaxPacketSize(DEFAULT_PACKET_SIZE);

                mPacketDecoder.setMaxPacketSize(DEFAULT_PACKET_SIZE);