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：
- 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）。
- 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。
- 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。
- 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。
- 接收方回复ACK。
接收方处理机制：
- 数据包序号正确（取反一致）-> ACK，否则NAK;
- 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。
- 校验和正确 ->ACK，否则 -> NACK
超时处理:
- 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。
- 当收到包时，接收过程中每个字符的超时间隔为 1 秒
- 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
- 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
- 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
