Mike Lockwood | f0a41d1 | 2015-03-24 08:27:11 -0700 | [diff] [blame] | 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 | |
| 17 | package com.android.bluetoothmidiservice; |
| 18 | |
| 19 | import android.media.midi.MidiReceiver; |
| 20 | import android.util.Log; |
| 21 | |
| 22 | import 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 | */ |
| 28 | public class BluetoothPacketDecoder extends PacketDecoder { |
| 29 | |
| 30 | private static final String TAG = "BluetoothPacketDecoder"; |
| 31 | |
| 32 | private final byte[] mBuffer; |
| 33 | |
| 34 | private final int TIMESTAMP_MASK_HIGH = 0x1F80; |
| 35 | private final int TIMESTAMP_MASK_LOW = 0x7F; |
| 36 | private final int HEADER_TIMESTAMP_MASK = 0x3F; |
| 37 | |
| 38 | public BluetoothPacketDecoder(int maxPacketSize) { |
| 39 | mBuffer = new byte[maxPacketSize]; |
| 40 | } |
| 41 | |
| 42 | @Override |
| 43 | public void decodePacket(byte[] buffer, MidiReceiver receiver) { |
| 44 | int length = buffer.length; |
| 45 | |
| 46 | // NOTE his code allows running status across packets, |
| 47 | // although the specification does not allow that. |
| 48 | |
| 49 | if (length < 1) { |
| 50 | Log.e(TAG, "empty packet"); |
| 51 | return; |
| 52 | } |
| 53 | byte header = buffer[0]; |
| 54 | if ((header & 0xC0) != 0x80) { |
| 55 | Log.e(TAG, "packet does not start with header"); |
| 56 | return; |
| 57 | } |
| 58 | |
| 59 | // shift bits 0 - 5 to bits 7 - 12 |
| 60 | int timestamp = (header & HEADER_TIMESTAMP_MASK) << 7; |
| 61 | boolean lastWasTimestamp = false; |
| 62 | int dataCount = 0; |
| 63 | int previousLowTimestamp = 0; |
| 64 | |
| 65 | // iterate through the rest of the packet, separating MIDI data from timestamps |
| 66 | for (int i = 1; i < buffer.length; i++) { |
| 67 | byte b = buffer[i]; |
| 68 | |
| 69 | if ((b & 0x80) != 0 && !lastWasTimestamp) { |
| 70 | lastWasTimestamp = true; |
| 71 | int lowTimestamp = b & TIMESTAMP_MASK_LOW; |
| 72 | int newTimestamp = (timestamp & TIMESTAMP_MASK_HIGH) | lowTimestamp; |
| 73 | if (lowTimestamp < previousLowTimestamp) { |
| 74 | newTimestamp = (newTimestamp + 0x0080) & TIMESTAMP_MASK_HIGH; |
| 75 | } |
| 76 | previousLowTimestamp = lowTimestamp; |
| 77 | |
| 78 | if (newTimestamp != timestamp) { |
| 79 | if (dataCount > 0) { |
| 80 | // send previous message separately since it has a different timestamp |
| 81 | try { |
| 82 | // FIXME use sendWithTimestamp |
| 83 | receiver.send(mBuffer, 0, dataCount); |
| 84 | } catch (IOException e) { |
| 85 | // ??? |
| 86 | } |
| 87 | dataCount = 0; |
| 88 | } |
| 89 | } |
| 90 | timestamp = newTimestamp; |
| 91 | } else { |
| 92 | lastWasTimestamp = false; |
| 93 | mBuffer[dataCount++] = b; |
| 94 | } |
| 95 | } |
| 96 | |
| 97 | if (dataCount > 0) { |
| 98 | try { |
| 99 | // FIXME use sendWithTimestamp |
| 100 | receiver.send(mBuffer, 0, dataCount); |
| 101 | } catch (IOException e) { |
| 102 | // ??? |
| 103 | } |
| 104 | } |
| 105 | } |
| 106 | } |