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POIssues receiving in RXTX
 

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    <p>I've been using RXTX for about a year now, without too many problems. I just started a new program to interact with a new piece of hardware, so I reused the connect() method I've used on my other projects, but I have a weird problem I've never seen before. </p> <p><strong>The Problem</strong></p> <p>The device works fine, because when I connect with HyperTerminal, I send things and receive what I expect, and <a href="http://www.serial-port-monitor.com/" rel="nofollow noreferrer">Serial Port Monitor</a>(SPM) reflects this. </p> <p>However, when I run the simple HyperTerminal-clone I wrote to diagnose the problem I'm having with my main app, bytes are sent, according to SPM, but nothing is received, and my SerialPortEventListener never fires. Even when I check for available data in the main loop, <code>reader.ready()</code> returns <code>false</code>. If I ignore this check, then I get an exception, details below.</p> <p><strong>Relevant section of connect() method</strong></p> <pre><code>// Configure and open port port = (SerialPort) CommPortIdentifier.getPortIdentifier(name) .open(owner,1000) port.setSerialPortParams(baud, databits, stopbits, parity); port.setFlowControlMode(fc_mode); final BufferedReader br = new BufferedReader( new InputStreamReader( port.getInputStream(), "US-ASCII")); // Add listener to print received characters to screen port.addEventListener(new SerialPortEventListener(){ public void serialEvent(SerialPortEvent ev) { try { System.out.println("Received: "+br.readLine()); } catch (IOException e) { e.printStackTrace(); } } }); port.notifyOnDataAvailable(); </code></pre> <p><strong>Exception</strong></p> <pre><code>java.io.IOException: Underlying input stream returned zero bytes at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:268) at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:306) at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:158) at java.io.InputStreamReader.read(InputStreamReader.java:167) at java.io.BufferedReader.fill(BufferedReader.java:136) at java.io.BufferedReader.read(BufferedReader.java:157) at &lt;my code&gt; </code></pre> <p><strong>The big question (again)</strong></p> <p>I think I've eliminated all possible hardware problems, so what could be wrong with my code, or the RXTX library? </p> <p><strong>Edit: something interesting</strong></p> <p>When I open HyperTerminal after sending a bunch of commands from java that should have gotten responses, all of the responses appear immediately, as if they had been put in the buffer somewhere, but unavailable.</p> <p><strong>Edit 2: Tried something new, same results</strong></p> <p>I ran the code example found <a href="http://rxtx.qbang.org/wiki/index.php/Two_way_communcation_with_the_serial_port" rel="nofollow noreferrer">here</a>, with the same results. No data came in, but when I switched to a new program, it came all at once.</p> <p><strong>Edit 3</strong></p> <p>The hardware is fine, and even a different computer has the same problem. I am not using any sort of USB adapter.</p> <p>I've started using <a href="http://technet.microsoft.com/en-us/sysinternals/bb896644.aspx" rel="nofollow noreferrer">PortMon</a>, too, and it's giving me some interesting results. HyperTerminal and RXTX are not using the same settings, and RXTX always polls the port, unlike HyperTerminal, but I still can't see what settings would affect this. As soon as I can isolate the configuration from the constant polling, I'll post my PortMon logs.</p> <p><strong>Edit 4</strong></p> <p>Is it possible that some sort of Windows update in the last 3 months could have caused this? It has screwed up one of my MATLAB mex-based programs once.</p> <p><strong>Edit 5</strong></p> <p>I've also noticed some things that are different between HyperTerminal, RXTX, and a separate program I found that communicates with the device (but doesn't do what I want, which is why I'm rolling my own program)</p> <ul> <li>HyperTerminal - set to no flow control, but Serial Port Monitor's RTS and DTR indicators are green</li> <li>Other program - not sure what settings it thinks it's using, but only SPM's RTS indicator is green</li> <li>RXTX - no matter what flow control I set, only SPM's CTS and DTR indicators are on.</li> </ul> <p>From Serial Port Monitor's help files (paraphrased): </p> <pre><code>the indicators display the state of the serial control lines RTS - Request To Send CTS - Clear To Send DTR - Data Terminal Ready </code></pre>
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