11个关键问题详解：理解与学习Xmodem协议必备指南
最编程
2024-02-23 12:46:51
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#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 last_error = 0;
#include "string.h"
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 (trychar == 'C') crc = 1;
trychar = 0;
p = xbuff;
*p++ = c;
for (i = 0; i < (bufsz+(crc?1:0)+3); ++i)
{
c = port_inbyte(DLY_1S);
if (last_error != 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)
{
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();
port_outbyte(CAN);
port_outbyte(CAN);
port_outbyte(CAN);
return -3;
}
port_outbyte(ACK);
continue;
}
reject:
flushinput();
port_outbyte(NAK);
}
}
int xmodemTransmit(unsigned char *src, int srcsz)
{
unsigned char xbuff[1030];
int bufsz, crc = -1;
unsigned char packetno = 1;
int i, c, len = 0;
int retry;
for(;;) {
for( retry = 0; retry < 16; ++retry)
{
c = port_inbyte((DLY_1S)<<1);
if (last_error == 0)
{
switch (c)
{
case 'C':
crc = 1;
goto start_trans;
case NAK:
crc = 0;
goto start_trans;
case CAN:
c = port_inbyte(DLY_1S);
if (c == CAN)
{
port_outbyte(ACK);
flushinput();
return -1;
}
break;
default:
break;
}
}
}
port_outbyte(CAN);
port_outbyte(CAN);
port_outbyte(CAN);
flushinput();
return -2;
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)
{
port_outbyte(xbuff[i]);
}
c = port_inbyte(DLY_1S);
if (last_error == 0 )
{
switch (c)
{
case ACK:
++packetno;
len += bufsz;
goto start_trans;
case CAN:
c = port_inbyte(DLY_1S);
if ( c == CAN)
{
port_outbyte(ACK);
flushinput();
return -1;
}
break;
case NAK:
default:
break;
}
}
}
port_outbyte(CAN);
port_outbyte(CAN);
port_outbyte(CAN);
flushinput();
return -4;
}
else
{
for (retry = 0; retry < 10; ++retry)
{
port_outbyte(EOT);
c = port_inbyte((DLY_1S)<<1);
if (c == ACK) break;
}
flushinput();
return (c == ACK)?len:-5;
}
}
}
}