1/*
2 * Copyright (C) 2015 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.android.bluetoothmidiservice;
18
19import android.media.midi.MidiReceiver;
20import android.util.Log;
21
22import java.io.IOException;
23
24/**
25 * This is an abstract base class that decodes a packet buffer and passes it to a
26 * {@link android.media.midi.MidiReceiver}
27 */
28public class BluetoothPacketDecoder extends PacketDecoder {
29
30    private static final String TAG = "BluetoothPacketDecoder";
31
32    private final byte[] mBuffer;
33    private MidiBtleTimeTracker mTimeTracker;
34
35    private final int TIMESTAMP_MASK_HIGH = 0x1F80;
36    private final int TIMESTAMP_MASK_LOW = 0x7F;
37    private final int HEADER_TIMESTAMP_MASK = 0x3F;
38
39    public BluetoothPacketDecoder(int maxPacketSize) {
40        mBuffer = new byte[maxPacketSize];
41    }
42
43    @Override
44    public void decodePacket(byte[] buffer, MidiReceiver receiver) {
45        if (mTimeTracker == null) {
46            mTimeTracker = new MidiBtleTimeTracker(System.nanoTime());
47        }
48
49        int length = buffer.length;
50
51        // NOTE his code allows running status across packets,
52        // although the specification does not allow that.
53
54        if (length < 1) {
55            Log.e(TAG, "empty packet");
56            return;
57        }
58        byte header = buffer[0];
59        if ((header & 0xC0) != 0x80) {
60            Log.e(TAG, "packet does not start with header");
61            return;
62        }
63
64        // shift bits 0 - 5 to bits 7 - 12
65        int highTimestamp = (header & HEADER_TIMESTAMP_MASK) << 7;
66        boolean lastWasTimestamp = false;
67        int dataCount = 0;
68        int previousLowTimestamp = 0;
69        long nanoTimestamp = 0;
70        int currentTimestamp = 0;
71
72        // iterate through the rest of the packet, separating MIDI data from timestamps
73        for (int i = 1; i < buffer.length; i++) {
74            byte b = buffer[i];
75
76            if ((b & 0x80) != 0 && !lastWasTimestamp) {
77                lastWasTimestamp = true;
78                int lowTimestamp = b & TIMESTAMP_MASK_LOW;
79                if (lowTimestamp < previousLowTimestamp) {
80                    highTimestamp = (highTimestamp + 0x0080) & TIMESTAMP_MASK_HIGH;
81                }
82                previousLowTimestamp = lowTimestamp;
83
84                int newTimestamp = highTimestamp | lowTimestamp;
85                if (newTimestamp != currentTimestamp) {
86                    if (dataCount > 0) {
87                        // send previous message separately since it has a different timestamp
88                        try {
89                            receiver.send(mBuffer, 0, dataCount, nanoTimestamp);
90                        } catch (IOException e) {
91                            // ???
92                        }
93                        dataCount = 0;
94                    }
95                    currentTimestamp = newTimestamp;
96                }
97
98                // calculate nanoTimestamp
99                long now = System.nanoTime();
100                nanoTimestamp = mTimeTracker.convertTimestampToNanotime(currentTimestamp, now);
101            } else {
102                lastWasTimestamp = false;
103                mBuffer[dataCount++] = b;
104            }
105        }
106
107        if (dataCount > 0) {
108            try {
109                receiver.send(mBuffer, 0, dataCount, nanoTimestamp);
110            } catch (IOException e) {
111                // ???
112            }
113        }
114    }
115}
116