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我有一个使用 USB 串行电缆 HL-340 连接到串行端口设备的树莓派（pl-2303 也经过测试）

该设备需要1 个字节的命令，并应以2 个字节回复（好的，这是一个非常简单的设备和非常容易学习的协议 :)）

我的代码：

[...]
        final int[] status = this.serialPort.getLinesStatus ( );
        final StringBuilder sb = new StringBuilder ( "Lines Status:" );
        final String[] name = new String[] { "CTS", "DSR", "RING", "RLSD" };
        for ( int i = 0; i < status.length; i++ )
          sb.append ( ( i > 0 ) ? "," : "" ).append ( name [i] ).append ( ':' ).append ( status [i] );
        System.out.println ( sb.toString ( ) );
        System.out.println ( "flowcontrol:" + this.serialPort.getFlowControlMode ( ) );
        this.serialPort.purgePort ( SerialPort.PURGE_RXCLEAR | SerialPort.PURGE_TXCLEAR );

        synchronized ( this )
        {
          System.out.println ( "1) getInputBufferBytesCount():" + this.serialPort.getInputBufferBytesCount ( ) );
          this.serialPort.addEventListener ( this );
          this.serialPort.setEventsMask ( SerialPort.MASK_RXCHAR );
          this.serialPort.writeBytes ( COMMAND );
          wait ( 3000 ); // wait 3 seconds for reply
          this.serialPort.removeEventListener ( );
          System.out.println ( "2) getInputBufferBytesCount():" + this.serialPort.getInputBufferBytesCount ( ) );
          final int n = this.serialPort.getInputBufferBytesCount ( );
          if ( n > 0 )
          {
            this.serialPort.readBytes ( n ); // purge garbage data?
            System.out.println ( "3) getInputBufferBytesCount():" + this.serialPort.getInputBufferBytesCount ( ) );
          }
        }  
        if ( ( this.data == null ) && ( this.error == null ) )
          this.error = "no response from device";
[...]

和回调代码：

@Override
public final void serialEvent ( final SerialPortEvent event )
{
  synchronized ( this )
  {
    try
    {
      final int val;
      if ( event.isRXCHAR ( ) )
        if ( (val = event.getEventValue ( )) == 2 ) // the reply is 2 bytes
          this.data = this.serialPort.readBytes ( 2 );
        else
          this.error = "unexpected value:" + val;
      else
        this.error = "unexpected event:" + event;
    }
    catch ( final Throwable x )
    {
      this.error = x.toString ( );
    }
    finally
    {
      notify ( );
    }
  }
}

结果非常奇怪且不可预测:(我希望设备的回复只有 2 个字节，但串行端口会通知我更多可供读取的数据：

Lines Status:CTS:0,DSR:0,RING:0,RLSD:0
flowcontrol:0
1) getInputBufferBytesCount():0
2) getInputBufferBytesCount():544
3) getInputBufferBytesCount():0
java.lang.Throwable: unexpected value:192

或者

Lines Status:CTS:0,DSR:0,RING:0,RLSD:0
flowcontrol:0
1) getInputBufferBytesCount():0
2) getInputBufferBytesCount():512
3) getInputBufferBytesCount():0
java.lang.Throwable: unexpected value:192

或者

Lines Status:CTS:0,DSR:0,RING:0,RLSD:0
flowcontrol:0
1) getInputBufferBytesCount():0
2) getInputBufferBytesCount():32
3) getInputBufferBytesCount():0
java.lang.Throwable: unexpected value:32

什么是问题？我应该更改哪些端口设置？

4

1 回答 1

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假设您正在等待 2 个字节的回复，现在在收到回复后打印缓冲区中的所有字节，以查看这是垃圾数据（特殊的不可打印字符）还是有效数据。这将为您提供更多洞察力和下一个行动项目以进一步取得进展。

于 2016-10-07T07:00:50.477 回答