java - Arduino Java SerialEvent 未被调用

Question

我正在遵循一个简单的例子found here (example one) ，将 Arduino 连接到 Raspberry Pi，并使用 Java 从 Raspberry Pi 上的 Arduino 读取一些数据。

问题是 SerialEvent 方法从未被调用，这意味着没有数据传入。但是，当我打开串行监视器时，我可以看到数据正在被正确读取。

也正在使用正确的串行端口。

这是 Java 代码。

// This class:

// - Starts up the communication with the Arduino.
// - Reads the data coming in from the Arduino and
//   converts that data in to a useful form.
// - Closes communication with the Arduino.

// Code builds upon this great example:
// http://www.csc.kth.se/utbildning/kth/kurser/DH2400/interak06/SerialWork.java
// The addition being the conversion from incoming characters to numbers.

// Load Libraries
import java.io.*;
import java.util.TooManyListenersException;

// Load RXTX Library
import gnu.io.*;

class ArduinoComm implements SerialPortEventListener
{
   // Used to in the process of converting the read in characters-
   // -first in to a string and then into a number.
   String rawStr = "";

   // Declare serial port variable
   SerialPort mySerialPort;

   // Declare input steam
   InputStream in;

   boolean stop = false;

   public void start(String portName, int baudRate)
   {
      stop = false;
      try
      {
         // Finds and opens the port
         CommPortIdentifier portId = CommPortIdentifier.getPortIdentifier(portName);
         mySerialPort = (SerialPort)portId.open("my_java_serial" + portName, 2000);
         System.out.println("Serial port found and opened");

         // Configures the port
         try
         {
            mySerialPort.setSerialPortParams(baudRate,
            mySerialPort.DATABITS_8,
            mySerialPort.STOPBITS_1,
            mySerialPort.PARITY_NONE);
            System.out.println("Serial port params set: " + baudRate);
         }
         catch (UnsupportedCommOperationException e)
         {
            System.out.println("Probably an unsupported Speed");
         }

         // Establish stream for reading from the port
         try
         {
            in = mySerialPort.getInputStream();
         }
         catch (IOException e)
         {
            System.out.println("couldn't get streams");
         }

         // We could read from "in" in a separate
         // thread, but the API gives us events
         try
         {
            mySerialPort.addEventListener(this);
            mySerialPort.notifyOnDataAvailable(true);
            System.out.println("Event listener added");
         }
         catch (TooManyListenersException e)
         {
            System.out.println("couldn't add listener");
         }
      }
      catch (Exception e)
      {
         System.out.println("Port in Use: " + e);
      }
   }

   // Used to close the serial port
   public void closeSerialPort()
   {
      try
      {
         in.close();
         stop = true;
         mySerialPort.close();
         System.out.println("Serial port closed");

      }
      catch (Exception e)
      {
      System.out.println(e);
      }
   }

   // Reads the incoming data packets from Arduino.
   public void serialEvent(SerialPortEvent event)
   {
      // Reads in data while data is available
      while (event.getEventType() == SerialPortEvent.DATA_AVAILABLE && stop == false)
      {
         try
         {
            // -------------------------------------------------------------------

            // Read in the available character
            char ch = (char)in.read();

            // If the read character is a letter this means
            // that we have found an identifier.
            if (Character.isLetter(ch) == true && rawStr != "")
            {
               // Convert the string containing all the characters
               // since the last identifier into an integer
               int value = Integer.parseInt(rawStr);

               if (ch == 'A')
               {
                  System.out.println("Value A is: " + value);
               }

               if (ch == 'B')
               {
                  System.out.println("Value B is: " + value);
               }

               // Reset rawStr ready for the next reading
               rawStr = ("");
            }
            else
            {
               // Add incoming characters to a string.
               // Only add characters to the string if they are digits.
               // When the Arduino starts up, the first characters
               // it sends through are S-t-a-r-t-
               // and so to avoid adding these characters, we
               // only add characters if they are digits.

               if (Character.isDigit(ch))
               {
                  rawStr = (rawStr + Character.toString(ch));
               }
               else
               {
                  System.out.print(ch);
               }
            }
         }
         catch (IOException e)
         {
         }
      }
   }

}

这是 Arduino 草图

// Arduino code for Part 01

// First we will define the values to be sent
// Note: The Java code to go with this example reads-
// -in integers so values will have to be sent as integers
int valueA = 21;
int valueB = 534;

void setup()
{
   Serial.begin(115200);
   Serial.println("Start");
}

void loop()
{
   // We send the value coupled with an identifier character
   // that both marks the end of the value and what the value is.

   Serial.print(valueA);
   Serial.print("A");

   Serial.print(valueB);
   Serial.print("B");

   // A delay to slow the program down to human pace.
   delay(500);
}

我读到，将 Serial.print 更改为 Serial.write 是执行此操作的新方法，但更改此方法没有结果。

Answer 1

所以没有触发事件的原因是程序在有机会之前退出并结束。

为了解决这个问题，我在主线程中添加了一个带有循环的线程。

public static void main(String[] args) throws Exception {
  ArduinoComm = new ArduinoComm ();
  main.start("/dev/ttyUSB0", 115200);
  Thread t = new Thread() {
    public void run() {
      try {
        // Messy implementation but it works for this demo purpose
        while(true) {
          // Optional sleep
          thread.Sleep(500);
        }
      }
      catch (InterruptedException ie) {
      }
    }
  };

  t.start();
  System.out.println("Started");
}

这是我的一个小小的疏忽。