Xmodem协议详解以及源代码.doc

文档介绍：Xmodem协议详解以及源代码
研究Xmodem协议必看的11个问题
原文地址:~type=v5_one&label=reltatic int last_error = 0;
#include ""
void port_outbyte(unsigned char trychar)
{
unsigned char buf[2];
buf[0] = trychar;
lowLevel_write(buf,1);
}
unsigned char port_inbyte(unsigned int time_out)
{
unsigned char ch;
int i;
last_error = 0;
if(lowLevel_read(&ch,1) == 1)
return ch;
last_error = 1;
return ch;
}
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 (port_inbyte(((DLY_1S)*3)>>1) >= 0)
;
}
int xmodemReceive(unsigned char *dest, int destsz)
{
unsigned char xbuff[1030];
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)
port_outbyte(trychar);
c = port_inbyte((DLY_1S)<<1);
if (last_error == 0)
{
switch (c)
{
case SOH:
bufsz = 128;
goto start_recv;
case STX:
bufsz = 1024;
goto start_recv;
case EOT:
flushinput();
port_outbyte(ACK);
return len;
case CAN:
c = port_inbyte(DLY_1S);
if (c == CAN)
{
flushinput();
port_outbyte(ACK);
return -1;
}
break;
default:
break;
}
}
}
if (trychar == 'C')
{
trychar = NAK;
continue;
}
flushinput();
port_outbyte(CAN);
port_outbyte(CAN);
port_outbyte(CAN);
return -2;
start_recv:
if (trycha