使用java实现Xmodem协议

发布时间：2020-05-25 04:20:53 所属栏目：Java 来源：互联网

导读：1.介绍Xmodem是一种在串口通信中广泛使用的异步文件传输协议，分为Xmodem（使用128字节的数据块）和1k-Xmodem（使用1024字节即1k字节的数据块）协议两种。

1.介绍

Xmodem是一种在串口通信中广泛使用的异步文件传输协议，分为Xmodem（使用128字节的数据块）和1k-Xmodem（使用1024字节即1k字节的数据块）协议两种。
本文实现的是128字节数据块的Xmodem协议，采用CRC16校验，在项目中应用时，发送端和接收端可根据具体情况修改双方的协议。
如果你对串口通信还不太了解，可以看下我写的这篇博客使用Java实现串口通信。

2.实现

在和嵌入式同学调试的过程中，发现发送端发送数据过快，导致接收端处理不过来，所以在send方法中开启了一个子线程来处理数据发送逻辑，方便加入延时处理。
接收方法中，发送C是表示以CRC方式校验。

public class Xmodem {

 // 开始
 private final byte SOH = 0x01;
 // 结束
 private final byte EOT = 0x04;
 // 应答
 private final byte ACK = 0x06;
 // 重传
 private final byte NAK = 0x15;
 // 无条件结束
 private final byte CAN = 0x18;

 // 以128字节块的形式传输数据
 private final int SECTOR_SIZE = 128;
 // 最大错误（无应答）包数
 private final int MAX_ERRORS = 10;

 // 输入流，用于读取串口数据
 private InputStream inputStream;
 // 输出流，用于发送串口数据
 private OutputStream outputStream;

 public Xmodem(InputStream inputStream,OutputStream outputStream) {
 this.inputStream = inputStream;
 this.outputStream = outputStream;
 }

 /**
 * 发送数据
 * 
 * @param filePath
 *  文件路径
 */
 public void send(final String filePath) {
 new Thread() {
  public void run() {
  try {
   // 错误包数
   int errorCount;
   // 包序号
   byte blockNumber = 0x01;
   // 校验和
   int checkSum;
   // 读取到缓冲区的字节数量
   int nbytes;
   // 初始化数据缓冲区
   byte[] sector = new byte[SECTOR_SIZE];
   // 读取文件初始化
   DataInputStream inputStream = new DataInputStream(
    new FileInputStream(filePath));

   while ((nbytes = inputStream.read(sector)) > 0) {
   // 如果最后一包数据小于128个字节，以0xff补齐
   if (nbytes < SECTOR_SIZE) {
    for (int i = nbytes; i < SECTOR_SIZE; i++) {
    sector[i] = (byte) 0xff;
    }
   }

   // 同一包数据最多发送10次
   errorCount = 0;
   while (errorCount < MAX_ERRORS) {
    // 组包
    // 控制字符 + 包序号 + 包序号的反码 + 数据 + 校验和
    putData(SOH);
    putData(blockNumber);
    putData(~blockNumber);
    checkSum = CRC16.calc(sector) & 0x00ffff;
    putChar(sector,(short) checkSum);
    outputStream.flush();

    // 获取应答数据
    byte data = getData();
    // 如果收到应答数据则跳出循环，发送下一包数据
    // 未收到应答，错误包数+1，继续重发
    if (data == ACK) {
    break;
    } else {
    ++errorCount;
    }
   }
   // 包序号自增
   blockNumber = (byte) ((++blockNumber) % 256);
   }

   // 所有数据发送完成后，发送结束标识
   boolean isAck = false;
   while (!isAck) {
   putData(EOT);
   isAck = getData() == ACK;
   }
  } catch (Exception e) {
   e.printStackTrace();
  }
  };
 }.start();
 }

 /**
 * 接收数据
 * 
 * @param filePath
 *  文件路径
 * @return 是否接收完成
 * @throws IOException
 *  异常
 */
 public boolean receive(String filePath) throws Exception {
 // 错误包数
 int errorCount = 0;
 // 包序号
 byte blocknumber = 0x01;
 // 数据
 byte data;
 // 校验和
 int checkSum;
 // 初始化数据缓冲区
 byte[] sector = new byte[SECTOR_SIZE];
 // 写入文件初始化
 DataOutputStream outputStream = new DataOutputStream(
  new FileOutputStream(filePath));

 // 发送字符C，CRC方式校验
 putData((byte) 0x43);

 while (true) {
  if (errorCount > MAX_ERRORS) {
  outputStream.close();
  return false;
  }

  // 获取应答数据
  data = getData();
  if (data != EOT) {
  try {
   // 判断接收到的是否是开始标识
   if (data != SOH) {
   errorCount++;
   continue;
   }

   // 获取包序号
   data = getData();
   // 判断包序号是否正确
   if (data != blocknumber) {
   errorCount++;
   continue;
   }

   // 获取包序号的反码
   byte _blocknumber = (byte) ~getData();
   // 判断包序号的反码是否正确
   if (data != _blocknumber) {
   errorCount++;
   continue;
   }

   // 获取数据
   for (int i = 0; i < SECTOR_SIZE; i++) {
   sector[i] = getData();
   }

   // 获取校验和
   checkSum = (getData() & 0xff) << 8;
   checkSum |= (getData() & 0xff);
   // 判断校验和是否正确
   int crc = CRC16.calc(sector);
   if (crc != checkSum) {
   errorCount++;
   continue;
   }

   // 发送应答
   putData(ACK);
   // 包序号自增
   blocknumber++;
   // 将数据写入本地
   outputStream.write(sector);
   // 错误包数归零
   errorCount = 0;

  } catch (Exception e) {
   e.printStackTrace();

  } finally {
   // 如果出错发送重传标识
   if (errorCount != 0) {
   putData(NAK);
   }
  }
  } else {
  break;
  }
 }

 // 关闭输出流
 outputStream.close();
 // 发送应答
 putData(ACK);

 return true;
 }

 /**
 * 获取数据
 * 
 * @return 数据
 * @throws IOException
 *  异常
 */
 private byte getData() throws IOException {
 return (byte) inputStream.read();
 }

 /**
 * 发送数据
 * 
 * @param data
 *  数据
 * @throws IOException
 *  异常
 */
 private void putData(int data) throws IOException {
 outputStream.write((byte) data);
 }

 /**
 * 发送数据
 * 
 * @param data
 *  数据
 * @param checkSum
 *  校验和
 * @throws IOException
 *  异常
 */
 private void putChar(byte[] data,short checkSum) throws IOException {
 ByteBuffer bb = ByteBuffer.allocate(data.length + 2).order(
  ByteOrder.BIG_ENDIAN);
 bb.put(data);
 bb.putShort(checkSum);
 outputStream.write(bb.array());
 }
}

CRC16校验算法，采用的是查表法。

public class CRC16 {

 private static final char crctable[] = { 0x0000,0x1021,0x2042,0x3063,0x4084,0x50a5,0x60c6,0x70e7,0x8108,0x9129,0xa14a,0xb16b,0xc18c,0xd1ad,0xe1ce,0xf1ef,0x1231,0x0210,0x3273,0x2252,0x52b5,0x4294,0x72f7,0x62d6,0x9339,0x8318,0xb37b,0xa35a,0xd3bd,0xc39c,0xf3ff,0xe3de,0x2462,0x3443,0x0420,0x1401,0x64e6,0x74c7,0x44a4,0x5485,0xa56a,0xb54b,0x8528,0x9509,0xe5ee,0xf5cf,0xc5ac,0xd58d,0x3653,0x2672,0x1611,0x0630,0x76d7,0x66f6,0x5695,0x46b4,0xb75b,0xa77a,0x9719,0x8738,0xf7df,0xe7fe,0xd79d,0xc7bc,0x48c4,0x58e5,0x6886,0x78a7,0x0840,0x1861,0x2802,0x3823,0xc9cc,0xd9ed,0xe98e,0xf9af,0x8948,0x9969,0xa90a,0xb92b,0x5af5,0x4ad4,0x7ab7,0x6a96,0x1a71,0x0a50,0x3a33,0x2a12,0xdbfd,0xcbdc,0xfbbf,0xeb9e,0x9b79,0x8b58,0xbb3b,0xab1a,0x6ca6,0x7c87,0x4ce4,0x5cc5,0x2c22,0x3c03,0x0c60,0x1c41,0xedae,0xfd8f,0xcdec,0xddcd,0xad2a,0xbd0b,0x8d68,0x9d49,0x7e97,0x6eb6,0x5ed5,0x4ef4,0x3e13,0x2e32,0x1e51,0x0e70,0xff9f,0xefbe,0xdfdd,0xcffc,0xbf1b,0xaf3a,0x9f59,0x8f78,0x9188,0x81a9,0xb1ca,0xa1eb,0xd10c,0xc12d,0xf14e,0xe16f,0x1080,0x00a1,0x30c2,0x20e3,0x5004,0x4025,0x7046,0x6067,0x83b9,0x9398,0xa3fb,0xb3da,0xc33d,0xd31c,0xe37f,0xf35e,0x02b1,0x1290,0x22f3,0x32d2,0x4235,0x5214,0x6277,0x7256,0xb5ea,0xa5cb,0x95a8,0x8589,0xf56e,0xe54f,0xd52c,0xc50d,0x34e2,0x24c3,0x14a0,0x0481,0x7466,0x6447,0x5424,0x4405,0xa7db,0xb7fa,0x8799,0x97b8,0xe75f,0xf77e,0xc71d,0xd73c,0x26d3,0x36f2,0x0691,0x16b0,0x6657,0x7676,0x4615,0x5634,0xd94c,0xc96d,0xf90e,0xe92f,0x99c8,0x89e9,0xb98a,0xa9ab,0x5844,0x4865,0x7806,0x6827,0x18c0,0x08e1,0x3882,0x28a3,0xcb7d,0xdb5c,0xeb3f,0xfb1e,0x8bf9,0x9bd8,0xabbb,0xbb9a,0x4a75,0x5a54,0x6a37,0x7a16,0x0af1,0x1ad0,0x2ab3,0x3a92,0xfd2e,0xed0f,0xdd6c,0xcd4d,0xbdaa,0xad8b,0x9de8,0x8dc9,0x7c26,0x6c07,0x5c64,0x4c45,0x3ca2,0x2c83,0x1ce0,0x0cc1,0xef1f,0xff3e,0xcf5d,0xdf7c,0xaf9b,0xbfba,0x8fd9,0x9ff8,0x6e17,0x7e36,0x4e55,0x5e74,0x2e93,0x3eb2,0x0ed1,0x1ef0 };

 public static char calc(byte[] bytes) {
 char crc = 0x0000;
 for (byte b : bytes) {
  crc = (char) ((crc << 8) ^ crctable[((crc >> 8) ^ b) & 0x00ff]);
 }
 return (char) (crc);
 }
}

3.使用

// serialPort为串口对象
Xmodem xmodem = new Xmodem(serialPort.getInputStream(),serialPort.getOutputStream());
// filePath为文件路径
// ./bin/xxx.bin
xmodem.send(filePath);

4.写在最后

完整的代码下载

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持编程小技巧。

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