使用java实现Xmodem协议
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。
publicclassXmodem{
//开始
privatefinalbyteSOH=0x01;
//结束
privatefinalbyteEOT=0x04;
//应答
privatefinalbyteACK=0x06;
//重传
privatefinalbyteNAK=0x15;
//无条件结束
privatefinalbyteCAN=0x18;
//以128字节块的形式传输数据
privatefinalintSECTOR_SIZE=128;
//最大错误（无应答）包数
privatefinalintMAX_ERRORS=10;
//输入流，用于读取串口数据
privateInputStreaminputStream;
//输出流，用于发送串口数据
privateOutputStreamoutputStream;
publicXmodem(InputStreaminputStream,OutputStreamoutputStream){
this.inputStream=inputStream;
this.outputStream=outputStream;
}
/**
*发送数据
*
*@paramfilePath
*文件路径
*/
publicvoidsend(finalStringfilePath){
newThread(){
publicvoidrun(){
try{
//错误包数
interrorCount;
//包序号
byteblockNumber=0x01;
//校验和
intcheckSum;
//读取到缓冲区的字节数量
intnbytes;
//初始化数据缓冲区
byte[]sector=newbyte[SECTOR_SIZE];
//读取文件初始化
DataInputStreaminputStream=newDataInputStream(
newFileInputStream(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(inti=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
bytedata=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
booleanisAck=false;
while(!isAck){
putData(EOT);
isAck=getData()==ACK;
}
}catch(Exceptione){
e.printStackTrace();
}
};
}.start();
}
/**
*接收数据
*
*@paramfilePath
*文件路径
*@return是否接收完成
*@throwsIOException
*异常
*/
publicbooleanreceive(StringfilePath)throwsException{
//错误包数
interrorCount=0;
//包序号
byteblocknumber=0x01;
//数据
bytedata;
//校验和
intcheckSum;
//初始化数据缓冲区
byte[]sector=newbyte[SECTOR_SIZE];
//写入文件初始化
DataOutputStreamoutputStream=newDataOutputStream(
newFileOutputStream(filePath));
//发送字符C，CRC方式校验
putData((byte)0x43);
while(true){
if(errorCount>MAX_ERRORS){
outputStream.close();
returnfalse;
}
//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(inti=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
intcrc=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(Exceptione){
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);
returntrue;
}
/**
*获取数据
*
*@return数据
*@throwsIOException
*异常
*/
privatebytegetData()throwsIOException{
return(byte)inputStream.read();
}
/**
*发送数据
*
*@paramdata
*数据
*@throwsIOException
*异常
*/
privatevoidputData(intdata)throwsIOException{
outputStream.write((byte)data);
}
/**
*发送数据
*
*@paramdata
*数据
*@paramcheckSum
*校验和
*@throwsIOException
*异常
*/
privatevoidputChar(byte[]data,shortcheckSum)throwsIOException{
ByteBufferbb=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。
publicclassCRC16{
privatestaticfinalcharcrctable[]={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};
publicstaticcharcalc(byte[]bytes){
charcrc=0x0000;
for(byteb:bytes){
crc=(char)((crc<<8)^crctable[((crc>>8)^b)&0x00ff]);
}
return(char)(crc);
}
}
3.使用
//serialPort为串口对象 Xmodemxmodem=newXmodem(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毛票票。