1.介紹
Xmodem是一種在串口通信中廣泛使用的異步文件傳輸協議,分為Xmodem(使用128字節的數據塊)和1k-Xmodem(使用1024字節即1k字節的數據塊)協議兩種。
本文實現的是128字節數據塊的Xmodem協議,採用CRC16校驗,在項目中應用時,發送端和接收端可根據具體情況修改雙方的協議。
如果你對串口通信還不太了解,可以看下我寫的這篇博客使用Java實現串口通信。
2.實現
在和嵌入式同學調試的過程中,發現發送端發送數據過快,導致接收端處理不過來,所以在send方法中開啟了一個子線程來處理數據發送邏輯,方便加入延時處理。
接收方法中,發送C是表示以CRC方式校驗。
public class Xmodem { // 開始private final byte SOH = 0x01; // 結束private final byte EOT = 0x04; // 應答private final byte ACK = 0x06; // 重傳private final byte NAK = 0x15; // 無條件結束private final byte CAN = 0x18; // 以128字節塊的形式傳輸數據private final int SECTOR_SIZE = 128; // 最大錯誤(無應答)包數private final int MAX_ERRORS = 10; // 輸入流,用於讀取串口數據private InputStream inputStream; // 輸出流,用於發送串口數據private OutputStream outputStream; public Xmodem(InputStream inputStream, OutputStream outputStream) { this.inputStream = inputStream; this.outputStream = outputStream; } /** * 發送數據* * @param filePath * 文件路徑*/ public void send(final String filePath) { new Thread() { public void run() { try { // 錯誤包數int errorCount; // 包序號byte blockNumber = 0x01; // 校驗和int checkSum; // 讀取到緩衝區的字節數量int nbytes; // 初始化數據緩衝區byte[] sector = new byte[SECTOR_SIZE]; // 讀取文件初始化DataInputStream inputStream = new DataInputStream( new FileInputStream(filePath)); while ((nbytes = inputStream.read(sector)) > 0) { // 如果最後一包數據小於128個字節,以0xff補齊if (nbytes < SECTOR_SIZE) { for (int i = nbytes; i < SECTOR_SIZE; i++) { sector[i] = (byte) 0xff; } } // 同一包數據最多發送10次errorCount = 0; while (errorCount < MAX_ERRORS) { // 組包// 控製字符+ 包序號+ 包序號的反碼+ 數據+ 校驗和putData(SOH); putData(blockNumber); putData(~blockNumber); checkSum = CRC16.calc(sector) & 0x00ffff; putChar(sector, (short) checkSum); outputStream.flush(); // 獲取應答數據byte data = getData(); // 如果收到應答數據則跳出循環,發送下一包數據// 未收到應答,錯誤包數+1,繼續重發if (data == ACK) { break; } else { ++errorCount; } } // 包序號自增blockNumber = (byte) ((++blockNumber) % 256); } // 所有數據發送完成後,發送結束標識boolean isAck = false; while (!isAck) { putData(EOT); isAck = getData() == ACK; } } catch (Exception e) { e.printStackTrace(); } }; }.start(); } /** * 接收數據* * @param filePath * 文件路徑* @return 是否接收完成* @throws IOException * 異常*/ public boolean receive(String filePath) throws Exception { // 錯誤包數int errorCount = 0; // 包序號byte blocknumber = 0x01; // 數據byte data; // 校驗和int checkSum; // 初始化數據緩衝區byte[] sector = new byte[SECTOR_SIZE]; // 寫入文件初始化DataOutputStream outputStream = new DataOutputStream( new FileOutputStream(filePath)); // 發送字符C,CRC方式校驗putData((byte) 0x43); while (true) { if (errorCount > MAX_ERRORS) { outputStream.close(); return false; } // 獲取應答數據data = getData(); if (data != EOT) { try { // 判斷接收到的是否是開始標識if (data != SOH) { errorCount++; continue; } // 獲取包序號data = getData(); // 判斷包序號是否正確if (data != blocknumber) { errorCount++; continue; } // 獲取包序號的反碼byte _blocknumber = (byte) ~getData(); // 判斷包序號的反碼是否正確if (data != _blocknumber) { errorCount++; continue; } // 獲取數據for (int i = 0; i < SECTOR_SIZE; i++) { sector[i] = getData(); } // 獲取校驗和checkSum = (getData() & 0xff) << 8; checkSum |= (getData() & 0xff); // 判斷校驗和是否正確int crc = CRC16.calc(sector); if (crc != checkSum) { errorCount++; continue; } // 發送應答putData(ACK); // 包序號自增blocknumber++; // 將數據寫入本地outputStream.write(sector); // 錯誤包數歸零errorCount = 0; } catch (Exception e) { e.printStackTrace(); } finally { // 如果出錯發送重傳標識if (errorCount != 0) { putData(NAK); } } } else { break; } } // 關閉輸出流outputStream.close(); // 發送應答putData(ACK); return true; } /** * 獲取數據* * @return 數據* @throws IOException * 異常*/ private byte getData() throws IOException { return (byte) inputStream.read(); } /** * 發送數據* * @param data * 數據* @throws IOException * 異常*/ private void putData(int data) throws IOException { outputStream.write((byte) data); } /** * 發送數據* * @param data * 數據* @param checkSum * 校驗和* @throws IOException * 異常*/ 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校驗算法,採用的是查表法。
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為串口對象Xmodem xmodem = new Xmodem(serialPort.getInputStream(),serialPort.getOutputStream());// filePath為文件路徑// ./bin/xxx.binxmodem.send(filePath);
4.寫在最後
完整的代碼下載
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