| /* |
| * Copyright (C) 2015 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package com.android.bluetoothmidiservice; |
| |
| import android.media.midi.MidiReceiver; |
| import android.util.Log; |
| |
| import java.io.IOException; |
| |
| /** |
| * This is an abstract base class that decodes a BLE-MIDI packet |
| * buffer and passes it to a {@link android.media.midi.MidiReceiver} |
| */ |
| public class BluetoothPacketDecoder extends PacketDecoder { |
| |
| private static final String TAG = "BluetoothPacketDecoder"; |
| |
| private final byte[] mBuffer; |
| private int mBytesInBuffer; |
| private MidiBtleTimeTracker mTimeTracker; |
| |
| private int mLowTimestamp; |
| private long mNanoTimestamp; |
| |
| private static final int TIMESTAMP_MASK_HIGH = 0x1F80; // top 7 bits |
| private static final int TIMESTAMP_MASK_LOW = 0x7F; // bottom 7 bits |
| private static final int HEADER_TIMESTAMP_MASK = 0x3F; // bottom 6 bits |
| |
| public BluetoothPacketDecoder(int maxPacketSize) { |
| mBuffer = new byte[maxPacketSize]; |
| } |
| |
| private void flushOutput(MidiReceiver receiver) { |
| if (mBytesInBuffer > 0) { |
| try { |
| receiver.send(mBuffer, 0, mBytesInBuffer, mNanoTimestamp); |
| } catch (IOException e) { |
| // ??? |
| } |
| mBytesInBuffer = 0; |
| } |
| } |
| |
| // NOTE: this code allows running status across packets, |
| // although the specification does not allow that. |
| @Override |
| public void decodePacket(byte[] buffer, MidiReceiver receiver) { |
| if (mTimeTracker == null) { |
| mTimeTracker = new MidiBtleTimeTracker(System.nanoTime()); |
| } |
| |
| int length = buffer.length; |
| if (length < 1) { |
| Log.e(TAG, "empty packet"); |
| return; |
| } |
| |
| byte header = buffer[0]; |
| // Check for the header bit 7. |
| // Ignore the reserved bit 6. |
| if ((header & 0x80) != 0x80) { |
| Log.e(TAG, "packet does not start with header"); |
| return; |
| } |
| |
| // shift bits 0 - 5 to bits 7 - 12 |
| int highTimestamp = (header & HEADER_TIMESTAMP_MASK) << 7; |
| boolean lastWasTimestamp = false; |
| int previousLowTimestamp = 0; |
| int currentTimestamp = highTimestamp | mLowTimestamp; |
| |
| // Iterate through the rest of the packet, separating MIDI data from timestamps. |
| for (int i = 1; i < buffer.length; i++) { |
| byte b = buffer[i]; |
| |
| // Is this a timestamp byte? |
| if ((b & 0x80) != 0 && !lastWasTimestamp) { |
| lastWasTimestamp = true; |
| mLowTimestamp = b & TIMESTAMP_MASK_LOW; |
| |
| // If the low timestamp byte wraps within the packet then |
| // increment the high timestamp byte. |
| if (mLowTimestamp < previousLowTimestamp) { |
| highTimestamp = (highTimestamp + 0x0080) & TIMESTAMP_MASK_HIGH; |
| } |
| previousLowTimestamp = mLowTimestamp; |
| |
| // If the timestamp advances then send any pending data. |
| int newTimestamp = highTimestamp | mLowTimestamp; |
| if (newTimestamp != currentTimestamp) { |
| // Send previous message separately since it has a different timestamp. |
| flushOutput(receiver); |
| currentTimestamp = newTimestamp; |
| } |
| |
| // Calculate MIDI nanosecond timestamp from BLE timestamp. |
| long now = System.nanoTime(); |
| mNanoTimestamp = mTimeTracker.convertTimestampToNanotime(currentTimestamp, now); |
| } else { |
| lastWasTimestamp = false; |
| // Flush if full before adding more data. |
| if (mBytesInBuffer == mBuffer.length) { |
| flushOutput(receiver); |
| } |
| mBuffer[mBytesInBuffer++] = b; |
| } |
| } |
| |
| flushOutput(receiver); |
| } |
| } |