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Xmodem Ymodem Zmodem 協議

本文轉載自   查看原文   2016-11-02 20:45   1421 

Xmodem

Xmodem協議是串行通信中的一種簡單的異步文件傳輸協議,可以作為嵌入式設備bootloader通過串口升級應用時的傳輸協議。

一個完整的數據包一共132字節，其中包含128字節數據。數據包以固定長度的3個字節幀頭開始，第一個是控制字符SOH（0x01），第二個是數據包序號（從1開始，1～255），第三個是數據包序號的反碼（255 - 序號），數據段固定長度為128個字節（不足128字節，使用控制字符CTRLZ(0x1A)補齊 ），最后一個校驗和（值為前邊所有字節相加的和模256的值。
數據包幀格式：

SOH (1Byte) | block number (1Byte) | inverse block number(1Byte) | data block(128Byte) | checksum(1Byte)

傳輸過程：

  1. 啟動傳輸時，接收方向發送方發送控制字符NAK（0x15），（僅僅發送一個字符格式，非數據包格式）。
  2. 當接收方的第一個NAK信號到達發送方時，傳輸開始，發送方將數據以每次128字節的數據加上包頭，包號，包號補碼，末尾加上校驗和，打包成幀格式傳送。
  3. 接收方正確接收到一個包的數據，發送控制字符ACK(0x06)給發送方；若接收出錯，發送控制字符NAK（0x15),則表示接收方請求重發剛才的數據包；如果發送方收到接收方傳 來的CAN字符(0x18)，則表示接收方請求無條件停止傳輸。
  4. 發送方發送完最后一個數據包，發送EOT（0x04）控制字符通知傳輸結束。
  5. 接收方回復ACK。

接收方處理機制：

  1. 數據包序號正確（取反一致）-> ACK，否則NAK;
  2. 是否為期望的包序號（包序號為前一個包序號+1或相同（重復包）） —> ACK， 否則 發送CAN中止傳輸。
  3. 校驗和正確 ->ACK，否則 -> NACK

超時處理:

  1. 啟動傳輸時，接收方等待一個信息包的到來所具有的超時時限為10秒，每個超時后發送 NAK。
  2. 當收到包時，接收過程中每個字符的超時間隔為 1 秒
  3. 為保持“接收方驅動”，發送方在等待一個啟動字節時不應該采用超時處理
  4. 一旦傳輸開始，發送方采用單獨的 1 分鍾超時時限，給接收方充足的時間做發送ACK ,NAK ,CAN 之前的必須處理
  5. 所有的超時及錯誤事件至少重試 10 次

控制字符
符合 ASICII 標准定義，長度均為 1 字節

> SOH 0x01
> EOT 0x04
> ACK 0x06
> NAK 0x15
> CAN 0x18

Xmodem-CRC

使用16位CRC校驗代替8位的和校驗，數據包格式：

SOH (1Byte) | block number (1Byte) | inverse block number(1Byte) | data block(128Byte) | 16-bit CRC(2Bytes)

啟動傳輸時，接收方向發送方發送控制字符"C"，代替NAK。若3秒后，無響應，切換到普通的和校驗模式，發送NAK。

Xmodem-1k

使用STX（0x02）代替SOH（0x01），數據塊的長度由128字節增加到1024字節，使用16bit-CRC校驗。

Ymodem

它包括XMODEM-1K的所有特征。
Ymodem允許批處理文件傳輸，效率更高。

Zmodem

modem則是改進的了Xmodem，它只需要對損壞的塊進行重發，其它正確的塊不需要發送確認字節。減少通信量。

SecureCRT仿真終端連接工具支持X/Ymodem協議方便的上傳下載文件。

Code

/*	
 * Copyright 2001-2010 Georges Menie (www.menie.org)
 * All rights reserved.
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the University of California, Berkeley nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE REGENTS AND CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/* this code needs standard functions memcpy() and memset()
   and input/output functions _inbyte() and _outbyte().

   the prototypes of the input/output functions are:
     int _inbyte(unsigned short timeout); // msec timeout
     void _outbyte(int c);

 */

#include "crc16.h"

#define SOH  0x01
#define STX  0x02
#define EOT  0x04
#define ACK  0x06
#define NAK  0x15
#define CAN  0x18
#define CTRLZ 0x1A

#define DLY_1S 1000
#define MAXRETRANS 25

static int check(int crc, const unsigned char *buf, int sz)
{
	if (crc) {
		unsigned short crc = crc16_ccitt(buf, sz);
		unsigned short tcrc = (buf[sz]<<8)+buf[sz+1];
		if (crc == tcrc)
			return 1;
	}
	else {
		int i;
		unsigned char cks = 0;
		for (i = 0; i < sz; ++i) {
			cks += buf[i];
		}
		if (cks == buf[sz])
		return 1;
	}

	return 0;
}

static void flushinput(void)
{
	while (_inbyte(((DLY_1S)*3)>>1) >= 0)
		;
}

int xmodemReceive(unsigned char *dest, int destsz)
{
	unsigned char xbuff[1030]; /* 1024 for XModem 1k + 3 head chars + 2 crc + nul */
	unsigned char *p;
	int bufsz, crc = 0;
	unsigned char trychar = 'C';
	unsigned char packetno = 1;
	int i, c, len = 0;
	int retry, retrans = MAXRETRANS;

	for(;;) {
		for( retry = 0; retry < 16; ++retry) {
			if (trychar) _outbyte(trychar);
			if ((c = _inbyte((DLY_1S)<<1)) >= 0) {
				switch (c) {
				case SOH:
					bufsz = 128;
					goto start_recv;
				case STX:
					bufsz = 1024;
					goto start_recv;
				case EOT:
					flushinput();
					_outbyte(ACK);
					return len; /* normal end */
				case CAN:
					if ((c = _inbyte(DLY_1S)) == CAN) {
						flushinput();
						_outbyte(ACK);
						return -1; /* canceled by remote */
					}
					break;
				default:
					break;
				}
			}
		}
		if (trychar == 'C') { trychar = NAK; continue; }
		flushinput();
		_outbyte(CAN);
		_outbyte(CAN);
		_outbyte(CAN);
		return -2; /* sync error */

	start_recv:
		if (trychar == 'C') crc = 1;
		trychar = 0;
		p = xbuff;
		*p++ = c;
		for (i = 0;  i < (bufsz+(crc?1:0)+3); ++i) {
			if ((c = _inbyte(DLY_1S)) < 0) goto reject;
			*p++ = c;
		}

		if (xbuff[1] == (unsigned char)(~xbuff[2]) && 
			(xbuff[1] == packetno || xbuff[1] == (unsigned char)packetno-1) &&
			check(crc, &xbuff[3], bufsz)) {
			if (xbuff[1] == packetno)	{
				register int count = destsz - len;
				if (count > bufsz) count = bufsz;
				if (count > 0) {
					memcpy (&dest[len], &xbuff[3], count);
					len += count;
				}
				++packetno;
				retrans = MAXRETRANS+1;
			}
			if (--retrans <= 0) {
				flushinput();
				_outbyte(CAN);
				_outbyte(CAN);
				_outbyte(CAN);
				return -3; /* too many retry error */
			}
			_outbyte(ACK);
			continue;
		}
	reject:
		flushinput();
		_outbyte(NAK);
	}
}

int xmodemTransmit(unsigned char *src, int srcsz)
{
	unsigned char xbuff[1030]; /* 1024 for XModem 1k + 3 head chars + 2 crc + nul */
	int bufsz, crc = -1;
	unsigned char packetno = 1;
	int i, c, len = 0;
	int retry;

	for(;;) {
		for( retry = 0; retry < 16; ++retry) {
			if ((c = _inbyte((DLY_1S)<<1)) >= 0) {
				switch (c) {
				case 'C':
					crc = 1;
					goto start_trans;
				case NAK:
					crc = 0;
					goto start_trans;
				case CAN:
					if ((c = _inbyte(DLY_1S)) == CAN) {
						_outbyte(ACK);
						flushinput();
						return -1; /* canceled by remote */
					}
					break;
				default:
					break;
				}
			}
		}
		_outbyte(CAN);
		_outbyte(CAN);
		_outbyte(CAN);
		flushinput();
		return -2; /* no sync */

		for(;;) {
		start_trans:
			xbuff[0] = SOH; bufsz = 128;
			xbuff[1] = packetno;
			xbuff[2] = ~packetno;
			c = srcsz - len;
			if (c > bufsz) c = bufsz;
			if (c >= 0) {
				memset (&xbuff[3], 0, bufsz);
				if (c == 0) {
					xbuff[3] = CTRLZ;
				}
				else {
					memcpy (&xbuff[3], &src[len], c);
					if (c < bufsz) xbuff[3+c] = CTRLZ;
				}
				if (crc) {
					unsigned short ccrc = crc16_ccitt(&xbuff[3], bufsz);
					xbuff[bufsz+3] = (ccrc>>8) & 0xFF;
					xbuff[bufsz+4] = ccrc & 0xFF;
				}
				else {
					unsigned char ccks = 0;
					for (i = 3; i < bufsz+3; ++i) {
						ccks += xbuff[i];
					}
					xbuff[bufsz+3] = ccks;
				}
				for (retry = 0; retry < MAXRETRANS; ++retry) {
					for (i = 0; i < bufsz+4+(crc?1:0); ++i) {
						_outbyte(xbuff[i]);
					}
					if ((c = _inbyte(DLY_1S)) >= 0 ) {
						switch (c) {
						case ACK:
							++packetno;
							len += bufsz;
							goto start_trans;
						case CAN:
							if ((c = _inbyte(DLY_1S)) == CAN) {
								_outbyte(ACK);
								flushinput();
								return -1; /* canceled by remote */
							}
							break;
						case NAK:
						default:
							break;
						}
					}
				}
				_outbyte(CAN);
				_outbyte(CAN);
				_outbyte(CAN);
				flushinput();
				return -4; /* xmit error */
			}
			else {
				for (retry = 0; retry < 10; ++retry) {
					_outbyte(EOT);
					if ((c = _inbyte((DLY_1S)<<1)) == ACK) break;
				}
				flushinput();
				return (c == ACK)?len:-5;
			}
		}
	}
}

#ifdef TEST_XMODEM_RECEIVE
int main(void)
{
	int st;

	printf ("Send data using the xmodem protocol from your terminal emulator now...\n");
	/* the following should be changed for your environment:
	   0x30000 is the download address,
	   65536 is the maximum size to be written at this address
	 */
	st = xmodemReceive((char *)0x30000, 65536);
	if (st < 0) {
		printf ("Xmodem receive error: status: %d\n", st);
	}
	else  {
		printf ("Xmodem successfully received %d bytes\n", st);
	}

	return 0;
}
#endif
#ifdef TEST_XMODEM_SEND
int main(void)
{
	int st;

	printf ("Prepare your terminal emulator to receive data now...\n");
	/* the following should be changed for your environment:
	   0x30000 is the download address,
	   12000 is the maximum size to be send from this address
	 */
	st = xmodemTransmit((char *)0x30000, 12000);
	if (st < 0) {
		printf ("Xmodem transmit error: status: %d\n", st);
	}
	else  {
		printf ("Xmodem successfully transmitted %d bytes\n", st);
	}

	return 0;
}
#endif


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