如何使用Java Android SDK中做好实时数据流 [英] How to do good real-time data streaming using Java Android SDK
问题描述
我有一个自制的蓝牙设备测量心电图在500Hz的：每2毫秒设备发送9个字节的数据（头，心电measurment，页脚）。因此，这是一个大致9 * 500 = 4.5kbytes / s的数据流。
I have a home-made bluetooth device measuring ECG at 500Hz: every 2 ms the device sends 9 bytes of data (header, ECG measurment, footer). So this is roughly a 9*500=4.5kbytes/s data stream.
我有一个C ++ Windows程序能够连接设备和检索数据流（使用Qt / QWT显示它）。在这种情况下，我使用的是Windows控制面板粘合装置，我使用boost serial_port接口，通过虚拟COM端口连接。这完美的作品，我收到我的数据流进行实时：我得到一个measurment点每2ms左右
I have a C++ Windows program able to connect the device and retrieve the data stream (displaying it with Qt/qwt). In this case, I use Windows control panel to bond the device and I connect it via a virtual COM port using boost serial_port interface. This works perfectly and I'm receiving my data stream in real time: I get a measurment point every 2ms or so.
我通过QtCreator 3.0.1（Qt的5.2.1）移植整个程序在Android上。看来，虚拟COM端口不能被提升访问（可能SDK权限将不会允许），所以我写了一篇Java的code打开和管理蓝牙连接。所以，我的应用程序仍然是C ++ / Qt的，但只有在连接并读取设备数据的层返工的Java（开放与createInsecureRfcommSocketToServiceRecord了连接）：
I ported the whole program on Android via QtCreator 3.0.1 (Qt 5.2.1). It appears that virtual COM ports cannot be accessed by boost (probably SDK permissions won't allow that) so I wrote a piece of Java code to open and manage the Bluetooth connection. So my app remains C++/Qt but only the layer connecting and reading data from the device was reworked in Java (opening the connexion with createInsecureRfcommSocketToServiceRecord):
Java的code读取数据：
Java code to read the data:
public int readData( byte[] buffer )
{
if( mInputStream == null )
{
traceErrorString("No connection, can't receive data");
}
else
{
try
{
final boolean verbose = false;
int available = mInputStream.available();
if ( verbose )
{
Calendar c = Calendar.getInstance();
Date date = new Date();
c.setTime(date);
c.get(Calendar.MILLISECOND);
SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");
String currentTime = sdf.format(date);
traceDebugString( currentTime + ":" + c.get(Calendar.MILLISECOND) + " - " + available + " bytes available, requested " + buffer.length );
}
if ( available >= buffer.length )
return mInputStream.read( buffer ); // only call read if we know it's not blocking
else
return 0;
}
catch (IOException e)
{
traceDebugString( "Failed to read data...disconnected?" );
}
}
return -1;
}
从C ++调用这样的：
Called from C++ like that:
bool ReceiveData( JNIEnv* env,
char* data,
size_t length,
bool& haserror )
{
bool result = false;
jbyteArray array = env->NewByteArray(length);
jint res = env->CallIntMethod(j_object, s_patchIfReceiveDataID, array );
if ( static_cast<size_t>(res) == length )
{
env->GetByteArrayRegion(array, 0, length, reinterpret_cast<jbyte*>(data));
result = true;
}
else if ( res == -1 )
{
haserror = true;
}
else
{
// not enough data in the stream buffer
haserror = false;
}
return result;
}
bool readThread( size_t blockSize )
{
BTGETANDCHECKENV // retrieving environment
char* buf = new char[blockSize];
bool haserror = false;
while ( !haserror )
{
if ( !ReceiveData( env, buf, blockSize, haserror ) )
{
// could not read data
if ( haserror )
{
// will stop this thread soon
}
else
{
boost::this_thread::sleep( boost::posix_time::milliseconds( 10 ) );
}
}
}
delete [] buf;
return true;
}
这适用于五个第一秒我gettings值排序的实时，那么pretty的好...
This works pretty well...for the five first seconds I'm gettings values in a sort of real time, then:
- 有时冻结，直到永远，这意味着mInputStream.available（）值仍低于要求。
- 有时冻结只为一秒钟左右，然后将其继续，但数据由1〜第二块被接收。含义mInputStream.available（）可以从0移动到超过3000两个呼叫（由10毫秒后）之间。事实上，我看到相同的过程中5首创秒，但缓冲可用性决不会超过150个字节，5秒钟后，它可以达到3000个字节。
下面是日志可以查看哪些详细当设置为true，如：
Here is what the log can look like when verbose is set to true:
14:59:30:756 - 0 bytes available, requested 3
14:59:30:767 - 0 bytes available, requested 3
14:59:30:778 - 0 bytes available, requested 3
14:59:30:789 - 1728 bytes available, requested 3
14:59:30:790 - 1725 bytes available, requested 6
14:59:30:792 - 1719 bytes available, requested 3
我的心电图设备绝对没有在11毫秒发送1728个字节！
My ECG device definitely did not send 1728 bytes in 11ms!!
我知道我的设备发送9个字节每2ms（否则，它不会对我的PC应用程序的工作）。看起来像Java做一些意想不到的缓冲，不会使现有9个字节每2ms .... 这也是奇怪的事情出现在开头做工精细的只有5秒。
I know my device sends 9 bytes every 2ms (otherwise, it would not work on my PC application). Looks like Java does some unexpected buffering and does not make available 9 bytes every 2ms.... It's also strange things appear to work fine for only 5 seconds at the beginning.
请注意，我试图使用的read（）不检查可用（）（堵版），但经历了完全一样的行为。
Note that I tried using read() without checking available() (blocking version) but experienced exactly the same behaviour.
所以，我不知道我在做什么错了......
So I'm wondering what I'm doing wrong...
- 有没有办法强制Java输入流进行自我更新？
- 有没有办法问Java来进行它的未完成的事件（像我们的QApplication :: processEvents）？
- 有没有全局设置，以指定缓冲区大小溪流（我没有发现任何在BluetoothDevice类/的BluetoothSocket级）
- 在PC上，打开虚拟COM端口的时候，我必须指定波特率，停止位，握手之类的东西。在Android上我刚打开RFCOMM插座没办法，难道这是问题（当时的心电图设备和智能手机将不会同步...）？
任何帮助或想法将受到欢迎！
Any help or idea would be welcomed!
编辑：我遇到的一台Nexus 5的手机，安卓4.4.2我只是测试相同的APK包在不同设备上：
I'm experiencing that on a Nexus 5 phone, Android 4.4.2 I just tested the same apk package on different devices:
- 银河S4采用Android 4.4.2：同样的问题
- 银河S3自定义的CyanogenMod 11的Android 4.4.2：数据流似乎完美，5秒和数据到达的实时后....不结冰使看起来像整个系统能够达到我想要的，但看起来像Android的默认设置使事情变得太慢....说不上来，如果有可能是一个设置在操作系统层面来解决这个问题而改变。
编辑：由于我没有答案:-(我试图用纯Java程序（没有C ++，没有Qt的）做同样的事情有同样的问题：<一href="http://stackoverflow.com/questions/27229813/real-time-bluetooth-spp-data-streaming-on-android-only-works-for-5-seconds">Real-time蓝牙SPP数据流在Android上只能持续5秒
As I got no answer :-( I tried to do the same thing using a pure Java program (no C++, no Qt). Had the same problem: Real-time Bluetooth SPP data streaming on Android only works for 5 seconds
推荐答案
这个问题显然是一个类似报道这里。
This problem is apparently similar to the one reported here.
5秒后，我无论是连接丢失，无论是实时流是显着放缓。
After 5 seconds, I had either a connection lost, either real-time streaming being dramatically slow down.
正如所说这里的Android> 4.3显然不喜欢单向通信超过5 secondes。所以，我现在发送假命令，设备每隔1 Seconde系列（一种保持活跃命令），现在Android是幸福的，因为它不是一个单向通信了......等等的数据流是经过好第五第二比以前！
As said here Android >4.3 apparently does not like one-way communication exceeding 5 secondes. So I'm now sending a dummy command to the device every 1 seconde (kind of "keep-alive" command) and now Android is happy because it's not a one-way communication anymore...and so data streaming is as good after the fifth second than before!
这篇关于如何使用Java Android SDK中做好实时数据流的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
