BluetoothMidiService: Use MidiBtleTimeTracker to interpret incoming Bluetooth MIDI timestamps (ff001809) · Commits · e / os / android_frameworks_base

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

+18 −9

Original line number	Diff line number	Diff line
		@@ -30,6 +30,7 @@ public class BluetoothPacketDecoder extends PacketDecoder {
		private static final String TAG = "BluetoothPacketDecoder";

		private final byte[] mBuffer;
		private MidiBtleTimeTracker mTimeTracker;

		private final int TIMESTAMP_MASK_HIGH = 0x1F80;
		private final int TIMESTAMP_MASK_LOW = 0x7F;
		@@ -41,6 +42,10 @@ public class BluetoothPacketDecoder extends PacketDecoder {

		@Override
		public void decodePacket(byte[] buffer, MidiReceiver receiver) {
		if (mTimeTracker == null) {
		mTimeTracker = new MidiBtleTimeTracker(System.nanoTime());
		}

		int length = buffer.length;

		// NOTE his code allows running status across packets,
		@@ -57,10 +62,12 @@ public class BluetoothPacketDecoder extends PacketDecoder {
		}

		// shift bits 0 - 5 to bits 7 - 12
		int timestamp = (header & HEADER_TIMESTAMP_MASK) << 7;
		int highTimestamp = (header & HEADER_TIMESTAMP_MASK) << 7;
		boolean lastWasTimestamp = false;
		int dataCount = 0;
		int previousLowTimestamp = 0;
		long nanoTimestamp = 0;
		int currentTimestamp = 0;

		// iterate through the rest of the packet, separating MIDI data from timestamps
		for (int i = 1; i < buffer.length; i++) {
		@@ -69,25 +76,28 @@ public class BluetoothPacketDecoder extends PacketDecoder {
		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;
		highTimestamp = (highTimestamp + 0x0080) & TIMESTAMP_MASK_HIGH;
		}
		previousLowTimestamp = lowTimestamp;

		if (newTimestamp != timestamp) {
		int newTimestamp = highTimestamp \| lowTimestamp;
		if (newTimestamp != currentTimestamp) {
		if (dataCount > 0) {
		// send previous message separately since it has a different timestamp
		try {
		// FIXME use sendWithTimestamp
		receiver.send(mBuffer, 0, dataCount);
		receiver.sendWithTimestamp(mBuffer, 0, dataCount, nanoTimestamp);
		} catch (IOException e) {
		// ???
		}
		dataCount = 0;
		}
		currentTimestamp = newTimestamp;
		}
		timestamp = newTimestamp;

		// calculate nanoTimestamp
		long now = System.nanoTime();
		nanoTimestamp = mTimeTracker.convertTimestampToNanotime(currentTimestamp, now);
		} else {
		lastWasTimestamp = false;
		mBuffer[dataCount++] = b;
		@@ -96,8 +106,7 @@ public class BluetoothPacketDecoder extends PacketDecoder {

		if (dataCount > 0) {
		try {
		// FIXME use sendWithTimestamp
		receiver.send(mBuffer, 0, dataCount);
		receiver.sendWithTimestamp(mBuffer, 0, dataCount, nanoTimestamp);
		} catch (IOException e) {
		// ???
		}

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

0 → 100644

+109 −0

Original line number	Diff line number	Diff line
		/*
		* 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;

		/**
		* Convert MIDI over BTLE timestamps to system nanotime.
		*/
		public class MidiBtleTimeTracker {

		public final static long NANOS_PER_MILLI = 1000000L;

		private final static long RANGE_MILLIS = 0x2000; // per MIDI / BTLE standard
		private final static long RANGE_NANOS = RANGE_MILLIS * NANOS_PER_MILLI;

		private int mWindowMillis = 20; // typical max connection interval
		private long mWindowNanos = mWindowMillis * NANOS_PER_MILLI;

		private int mPreviousTimestamp; // Used to calculate deltas.
		private long mPreviousNow;
		// Our model of the peripherals millisecond clock.
		private long mPeripheralTimeMillis;
		// Host time that corresponds to time=0 on the peripheral.
		private long mBaseHostTimeNanos;
		private long mPreviousResult; // To prevent retrograde timestamp

		public MidiBtleTimeTracker(long now) {
		mPeripheralTimeMillis = 0;
		mBaseHostTimeNanos = now;
		mPreviousNow = now;
		}

		/**
		* @param timestamp
		* 13-bit millis in range of 0 to 8191
		* @param now
		* current time in nanoseconds
		* @return nanoseconds corresponding to the timestamp
		*/
		public long convertTimestampToNanotime(int timestamp, long now) {
		long deltaMillis = timestamp - mPreviousTimestamp;
		// will be negative when timestamp wraps
		if (deltaMillis < 0) {
		deltaMillis += RANGE_MILLIS;
		}
		mPeripheralTimeMillis += deltaMillis;

		// If we have not been called for a long time then
		// make sure we have not wrapped multiple times.
		if ((now - mPreviousNow) > (RANGE_NANOS / 2)) {
		// Handle missed wraps.
		long minimumTimeNanos = (now - mBaseHostTimeNanos)
		- (RANGE_NANOS / 2);
		long minimumTimeMillis = minimumTimeNanos / NANOS_PER_MILLI;
		while (mPeripheralTimeMillis < minimumTimeMillis) {
		mPeripheralTimeMillis += RANGE_MILLIS;
		}
		}

		// Convert peripheral time millis to host time nanos.
		long timestampHostNanos = (mPeripheralTimeMillis * NANOS_PER_MILLI)
		+ mBaseHostTimeNanos;

		// The event cannot be in the future. So move window if we hit that.
		if (timestampHostNanos > now) {
		mPeripheralTimeMillis = 0;
		mBaseHostTimeNanos = now;
		timestampHostNanos = now;
		} else {
		// Timestamp should not be older than our window time.
		long windowBottom = now - mWindowNanos;
		if (timestampHostNanos < windowBottom) {
		mPeripheralTimeMillis = 0;
		mBaseHostTimeNanos = windowBottom;
		timestampHostNanos = windowBottom;
		}
		}
		// prevent retrograde timestamp
		if (timestampHostNanos < mPreviousResult) {
		timestampHostNanos = mPreviousResult;
		}
		mPreviousResult = timestampHostNanos;
		mPreviousTimestamp = timestamp;
		mPreviousNow = now;
		return timestampHostNanos;
		}

		public int getWindowMillis() {
		return mWindowMillis;
		}

		public void setWindowMillis(int window) {
		this.mWindowMillis = window;
		}

		}