xmoderm.c

c8051f310xmodembootloader.rar

/*
	Copyright 2001, 2002 Georges Menie (www.menie.org)

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/

/* 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);

 */
/*
//---------------------------------------- XMODEM protocol ------------------------------------------------------------//
XMODEM, like most file transfer protocols, breaks up the original data into a series of "packets" that are sent to the receiver, 
along with additional information allowing the receiver to determine whether that packet was correctly received.


[edit] Packet structure
The original XMODEM used a 128-byte data packet, the basic block size used on CP/M floppy disks.
The packet was prefixed by a simple 3-byte header containing a <SOH> character, a "block number" from 0-255, and the "inverse" block number