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PORXTX serial connection - issue with blocking read()
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5219450
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CreationDate
2011-03-07T12:00:45.500
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2014-11-12T21:35:18.337
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2014-09-11T14:52:22.583
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Body
I am trying to use the RXTX library for blocking serial communication on Windows (XP and 7). I have tested the connection with Hyperterminal in both ends, and it works flawlessly. I set up the connection with the following code: (exception handling and defensive checks omitted for clarity) <pre><code>private InputStream inStream; private OutputStream outStream; private BufferedReader inReader; private PrintWriter outWriter; private SerialPort serialPort; private final String serialPortName; public StreamComSerial(String serialPortName) { this.serialPortName = serialPortName; CommPortIdentifier portIdentifier; portIdentifier = CommPortIdentifier.getPortIdentifier(serialPortName); CommPort commPort = null; commPort = portIdentifier.open(this.getClass().getName(),500); serialPort = (SerialPort) commPort; serialPort.setSerialPortParams(4800,SerialPort.DATABITS_8,SerialPort.STOPBITS_1,SerialPort.PARITY_NONE); inStream = serialPort.getInputStream(); outStream = serialPort.getOutputStream(); inReader = new BufferedReader(new InputStreamReader(inStream, Settings.getCharset())); outWriter = new PrintWriter(new OutputStreamWriter(outStream, Settings.getCharset())); </code></pre> When I use <pre><code>outWriter.println("test message"); flush(); </code></pre> the message is recieved fine on the other end, but calling <pre><code>inReader.readLine() </code></pre> imidiately returns "java.io.IOException: Underlying input stream returned zero bytes". I then decided to try and implement my own blocking read logic and wrote this: <pre><code>public String readLine() throws IOException { String line = new String(); byte[] nextByte = {-1}; while (true) { nextByte[0] = (byte)inStream.read(); logger.debug("int read: " + nextByte[0]); if (nextByte[0] == (byte)-1) { try { Thread.sleep(100); } catch (InterruptedException e) { e.printStackTrace(); } continue; } logger.debug("byte read: " + nextByte[0]); line = line + new String(nextByte); if (nextByte[0] == (byte)13) { // 13 is carriage return in ASCII return line; } } } </code></pre> But this code goes in an infinite loop and "nextByte[0] = (byte)inStream.read();" assigns -1 no matter what is sent over the serial connection. In addition, the other end stutters quite badly and only lets me send a character every 1-3 sec. and hangs for a long time if I try to send many characters in a short burst. Any help very appreciated. *edit - using inStream.read(nextByte) instead of "nextByte[0] = (byte)inStream.read();" does not write to the nextByte variable, no matter what I send to it through the serial connection. *edit2 - as my code works flawlessly with the SUN javax.comm lib and a win32com.dll I got from a friend, I have ceased trying to make it work with RXTX. I am not interested in unblocking communication, which seems to be the only way other people can make RXTX work.
Tags
<java><serial-port><rxtx>
Title
RXTX serial connection - issue with blocking read()
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