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/*
* 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 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 final int TIMESTAMP_MASK_HIGH = 0x1F80;
private final int TIMESTAMP_MASK_LOW = 0x7F;
private final int HEADER_TIMESTAMP_MASK = 0x3F;
public BluetoothPacketDecoder(int maxPacketSize) {
mBuffer = new byte[maxPacketSize];
}
@Override
public void decodePacket(byte[] buffer, MidiReceiver receiver) {
int length = buffer.length;
// NOTE his code allows running status across packets,
// although the specification does not allow that.
if (length < 1) {
Log.e(TAG, "empty packet");
return;
}
byte header = buffer[0];
if ((header & 0xC0) != 0x80) {
Log.e(TAG, "packet does not start with header");
return;
}
// shift bits 0 - 5 to bits 7 - 12
int timestamp = (header & HEADER_TIMESTAMP_MASK) << 7;
boolean lastWasTimestamp = false;
int dataCount = 0;
int previousLowTimestamp = 0;
// iterate through the rest of the packet, separating MIDI data from timestamps
for (int i = 1; i < buffer.length; i++) {
byte b = buffer[i];
if ((b & 0x80) != 0 && !lastWasTimestamp) {
lastWasTimestamp = true;
int lowTimestamp = b & TIMESTAMP_MASK_LOW;
int newTimestamp = (timestamp & TIMESTAMP_MASK_HIGH) | lowTimestamp;
if (lowTimestamp < previousLowTimestamp) {
newTimestamp = (newTimestamp + 0x0080) & TIMESTAMP_MASK_HIGH;
}
previousLowTimestamp = lowTimestamp;
if (newTimestamp != timestamp) {
if (dataCount > 0) {
// send previous message separately since it has a different timestamp
try {
// FIXME use sendWithTimestamp
receiver.send(mBuffer, 0, dataCount);
} catch (IOException e) {
// ???
}
dataCount = 0;
}
}
timestamp = newTimestamp;
} else {
lastWasTimestamp = false;
mBuffer[dataCount++] = b;
}
}
if (dataCount > 0) {
try {
// FIXME use sendWithTimestamp
receiver.send(mBuffer, 0, dataCount);
} catch (IOException e) {
// ???
}
}
}
}
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