java - Arduino 与 Java 接口(interface)问题

Question

我关注了Interfacing with Java tutorial ，但在测试时遇到了一些问题。目前，当我尝试手动输入时，我的 Arduino 程序运行良好。

Arduino 上的 C 代码段:

char line[20];
int line_pos = 0;
char action[10];
unsigned long duration;
boolean data_ready = false;

void setup()
{
  Serial.begin(9600);
  delay(1500);
  Serial.println("Ready!");
}

void loop()
{
char state;
if(Serial.available()>0)
{
    delay(20);
    state = Serial.read();

    if(state == '!')
    {
      data_ready = true;
      line[line_pos] = state;
      line_pos = 0;
    }
    else
    {
      line[line_pos] = state;
      line_pos = line_pos + 1;
    }

    if(data_ready == true)
    {
        split(line);
        Serial.print(action);
        delay(20);
        Serial.print("!");
        delay(20);
        Serial.print(duration);
        delay(20);
        Serial.print("!");

        Serial.println("Data has been split");

        if(strcmp(action, "left") == 0)
        {
            Serial.println("Received left");
        }
        else if(strcmp(action, "right") == 0)
        {
            Serial.println("Received rightt");
        }
        else if(strcmp(action, "straight") == 0)
        {
            Serial.println("Received straight");
        }

        memset(line, 0, 20);
        data_ready = false;
    }
    }
}  

void split(char input[20])
{
char *param, *ptr;

param = strtok_r(input, "#", &ptr);
strncpy(action, param, sizeof(action));
action[sizeof(action)-1] = '\0';

param = strtok_r(NULL, "!", &ptr);
duration = strtoul(param, &param, 10);
}

当我输入“left#123!”时我在 COM 中得到以下输出，其结果符合预期。这里没有问题:

准备好了! left!123!数据已分割 收到左侧

现在这是我的 Java 代码:

import java.io.InputStream;
import java.io.OutputStream;
import gnu.io.CommPortIdentifier; 
import gnu.io.SerialPort;
import gnu.io.SerialPortEvent; 
import gnu.io.SerialPortEventListener; 
import java.util.Enumeration;

public class SerialTest implements SerialPortEventListener {
    SerialPort serialPort;
        /** The port we're normally going to use. */
    private static final String PORT_NAMES[] = { 
            "/dev/tty.usbserial-A9007UX1", // Mac OS X
            "/dev/ttyUSB0", // Linux
        "COM3", // Windows
        };
/** Buffered input stream from the port */
private InputStream input;
/** The output stream to the port */
private OutputStream output;
/** Milliseconds to block while waiting for port open */
private static final int TIME_OUT = 2000;
/** Default bits per second for COM port. */
private static final int DATA_RATE = 9600;

private String display = "";

public void initialize() {
    CommPortIdentifier portId = null;
    Enumeration portEnum = CommPortIdentifier.getPortIdentifiers();

    // iterate through, looking for the port
    while (portEnum.hasMoreElements()) {
        CommPortIdentifier currPortId = (CommPortIdentifier) portEnum.nextElement();
        for (String portName : PORT_NAMES) {
            if (currPortId.getName().equals(portName)) {
                portId = currPortId;
                break;
            }
        }
    }

    if (portId == null) {
        System.out.println("Could not find COM port.");
        return;
    }

    try {
        // open serial port, and use class name for the appName.
        serialPort = (SerialPort) portId.open(this.getClass().getName(),
                TIME_OUT);

        // set port parameters
        serialPort.setSerialPortParams(DATA_RATE,
                SerialPort.DATABITS_8,
                SerialPort.STOPBITS_1,
                SerialPort.PARITY_NONE);

        // open the streams
        input = serialPort.getInputStream();
        output = serialPort.getOutputStream();

        // add event listeners
        serialPort.addEventListener(this);
        serialPort.notifyOnDataAvailable(true);
    } catch (Exception e) {
        System.err.println(e.toString());
    }
}

/**
 * This should be called when you stop using the port.
 * This will prevent port locking on platforms like Linux.
 */
public synchronized void close() {
    if (serialPort != null) {
        serialPort.removeEventListener();
        serialPort.close();
    }
}

/**
 * Handle an event on the serial port. Read the data and print it.
 */
public synchronized void serialEvent(SerialPortEvent oEvent) {
    if (oEvent.getEventType() == SerialPortEvent.DATA_AVAILABLE) {
        try {
            int available = input.available();
            byte chunk[] = new byte[available];
            input.read(chunk, 0, available);

            System.out.println(display);

            display += (new String(chunk)).trim();
            if(display.contains("!"))
            {
                display = display.substring(0, display.indexOf("!"));

                if(display.equals("Ready"))
                {
                    String reply = "left#123!";
                    byte reply_byte[] = new byte[reply.length()];
                    reply_byte = reply.getBytes("UTF-16LE");
                    output.write(reply_byte);
                }

                display = "";
            }

        } catch (Exception e) {
            System.err.println(e.toString());
        }
    }
    // Ignore all the other eventTypes, but you should consider the other ones.
}

public static void main(String[] args) throws Exception {
    SerialTest main = new SerialTest();
    main.initialize();
    System.out.println("Started");
}
}

下面是 Java 代码在控制台中打印出来的内容:

雷亚 我 0 数据 数据哈斯 数据哈斯比 数据已被sp 数据已拆分

串行输入的读取似乎并不流畅，而是重复的部分。有人可以帮我诊断问题并给我解决方案吗？

Answer 1

这里至少有两件事需要注意，但这是基于我对 Java 以外的语言的经验，因此它的行为方式可能不完全相同。

第一个是该事件看起来像是在少数字符后被触发的，也许您的 Arduino 发送速度不够快，无法一次全部显示。这会导致您的 Java 代码重复输出，因为您正在打印 display，然后将新的 chunk 附加到其中。如果您没有找到感叹号，它永远不会被清除。您最好打印 chunk 来准确查看您收到的内容。

第二个是您可能只接收新数据的事件，因此如果在触发事件和调用 input.read() 之间出现新数据，则不会触发另一个事件。最好在事件处理程序中设置一个循环，在仍然有可用数据时继续循环，例如:

public synchronized void serialEvent(SerialPortEvent oEvent) {
    if (oEvent.getEventType() == SerialPortEvent.DATA_AVAILABLE) {
        try {
            int available = input.available();
            while (available > 0)
            {
                byte chunk[] = new byte[available];
                input.read(chunk, 0, available);

                System.out.println(new String(chunk));

                // Perform your packet processing here

                // See if there is any more data that came in while we were
                // processing the event
                available = input.available();
            }

        } catch (Exception e) {
            System.err.println(e.toString());
        }
    }
    // Ignore all the other eventTypes, but you should consider the other ones.
}