Xmodem Ymodem Zmodem 协议

Xmodem

Xmodem协议是串行通信中的一种简单的异步文件传输协议,可以作为嵌入式设备bootloader通过串口升级应用时的传输协议。

一个完整的数据包一共132字节,其中包含128字节数据。数据包以固定长度的3个字节帧头开始,第一个是控制字符SOH(0x01),第二个是数据包序号(从1开始,1~255),第三个是数据包序号的反码(255 - 序号),数据段固定长度为128个字节(不足128字节,使用控制字符CTRLZ(0x1A)补齐 ),最后一个校验和(值为前边所有字节相加的和模256的值。
数据包帧格式

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

传输过程

  1. 启动传输时,接收方向发送方发送控制字符NAK(0x15),(仅仅发送一个字符格式,非数据包格式)。
  2. 当接收方的第一个NAK信号到达发送方时,传输开始,发送方将数据以每次128字节的数据加上包头,包号,包号补码,末尾加上校验和,打包成帧格式传送。
  3. 接收方正确接收到一个包的数据,发送控制字符ACK(0x06)给发送方;若接收出错,发送控制字符NAK(0x15),则表示接收方请求重发刚才的数据包;如果发送方收到接收方传 来的CAN字符(0x18),则表示接收方请求无条件停止传输。
  4. 发送方发送完最后一个数据包,发送EOT(0x04)控制字符通知传输结束。
  5. 接收方回复ACK。

接收方处理机制

  1. 数据包序号正确(取反一致)-> ACK,否则NAK;
  2. 是否为期望的包序号(包序号为前一个包序号+1或相同(重复包)) —> ACK, 否则 发送CAN中止传输。
  3. 校验和正确 ->ACK,否则 -> NACK

超时处理:

  1. 启动传输时,接收方等待一个信息包的到来所具有的超时时限为10秒,每个超时后发送 NAK。
  2. 当收到包时,接收过程中每个字符的超时间隔为 1 秒
  3. 为保持“接收方驱动”,发送方在等待一个启动字节时不应该采用超时处理
  4. 一旦传输开始,发送方采用单独的 1 分钟超时时限,给接收方充足的时间做发送ACK ,NAK ,CAN 之前的必须处理
  5. 所有的超时及错误事件至少重试 10 次

控制字符
符合 ASICII 标准定义,长度均为 1 字节

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

Xmodem-CRC

使用16位CRC校验代替8位的和校验,数据包格式:

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

启动传输时,接收方向发送方发送控制字符"C",代替NAK。若3秒后,无响应,切换到普通的和校验模式,发送NAK。

Xmodem-1k

使用STX(0x02)代替SOH(0x01),数据块的长度由128字节增加到1024字节,使用16bit-CRC校验。

Ymodem

它包括XMODEM-1K的所有特征。
Ymodem允许批处理文件传输,效率更高。

Zmodem

modem则是改进的了Xmodem,它只需要对损坏的块进行重发,其它正确的块不需要发送确认字节。减少通信量。

SecureCRT仿真终端连接工具支持X/Ymodem协议方便的上传下载文件。

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

posted on 2016-11-02 20:45 packer 阅读(...) 评论(...) 编辑 收藏

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