unsigned int calculate_crc(unsigned char *ptr,unsigned char datacount)
{
unsigned int crc=0;
while(datacount--)
crc=xmodem_crc_check(crc,*ptr++);
return crc;
}
long xmodem_receive( char* dest, u32 limit )
{
unsigned char xmbuf[XMODEM_BUFFER_SIZE+6];
unsigned char seqnum=1; // xmodem sequence number starts at 1
unsigned short pktsize=128; // default packet size is 128 bytes
unsigned char response='C'; // solicit a connection with CRC
char retry=XMODEM_RETRY_LIMIT;
unsigned char crcflag=0;
unsigned long totalbytes=0;
int i,c;
while(retry > 0)
{
// solicit a connection/packet
xmodem_out_func(response);
// wait for start of packet
if( (c = xmodem_in_func(XMODEM_TIMEOUT_DELAY)) >= 0)
{
switch(c)
{
case SOH:
pktsize = 128;
break;
case EOT:
xmodem_flush();
xmodem_out_func(ACK);
// completed transmission normally
return totalbytes;
case CAN:
if((c = xmodem_in_func(XMODEM_TIMEOUT_DELAY)) == CAN)
{
xmodem_flush();
xmodem_out_func(ACK);
// transaction cancelled by remote node
return XMODEM_ERROR_REMOTECANCEL;
}
default:
break;
}
}
else
{
// timed out, try again
// no need to flush because receive buffer is already empty
retry--;
//response = NAK;
continue;
}
// check if CRC mode was accepted
if(response == 'C') crcflag = 1;
// got SOH/STX, add it to processing buffer
xmbuf[0] = c;
// try to get rest of packet
for(i=0; i<(pktsize+crcflag+4-1); i++)
{
if((c = xmodem_in_func(XMODEM_TIMEOUT_DELAY)) >= 0)
{
xmbuf[1+i] = c;
}
else
{
// timed out, try again
retry--;
xmodem_flush();
response = NAK;
break;
}
}
// packet was too small, retry
if(i<(pktsize+crcflag+4-1))
continue;
// got whole packet
// check validity of packet
if( (xmbuf[1] == (unsigned char)(~xmbuf[2])) && // sequence number was transmitted w/o error
xmodem_crc_check(crcflag, &xmbuf[3], pktsize) ) // packet is not corrupt
{
// is this the packet we were waiting for?
if(xmbuf[1] == seqnum)
{
// write/deliver data
if( totalbytes + pktsize > limit )
{
// Cancel transmission
xmodem_flush();
xmodem_out_func(CAN);
xmodem_out_func(CAN);
xmodem_out_func(CAN);
return XMODEM_ERROR_OUTOFMEM;
}
memcpy( dest + totalbytes, xmbuf + 3, pktsize );
totalbytes += pktsize;
// next sequence number
seqnum++;
// reset retries
retry = XMODEM_RETRY_LIMIT;
// reply with ACK
response = ACK;
continue;
}
else if(xmbuf[1] == (unsigned char)(seqnum-1))
{
// this is a retransmission of the last packet
// ACK and move on
response = ACK;
continue;
}
else
{
// we are completely out of sync
// cancel transmission
xmodem_flush();
xmodem_out_func(CAN);
xmodem_out_func(CAN);
xmodem_out_func(CAN);
return XMODEM_ERROR_OUTOFSYNC;
}
}
else
{
// packet was corrupt
// NAK it and try again
retry--;
xmodem_flush();
response = NAK;
continue;
}
}
// exceeded retry count
xmodem_flush();
xmodem_out_func(CAN);
xmodem_out_func(CAN);
xmodem_out_func(CAN);
return XMODEM_ERROR_RETRYEXCEED;
}
