contiki/uip/uip-split.c

/*
 * Copyright (c) 2004, Swedish Institute of Computer Science.
 * All rights reserved. 
 *
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions 
 * are met: 
 * 1. Redistributions of source code must retain the above copyright 
 *    notice, this list of conditions and the following disclaimer. 
 * 2. 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. 
 * 3. Neither the name of the Institute 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 INSTITUTE 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 INSTITUTE OR 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 file is part of the Contiki operating system.
 * 
 * Author: Adam Dunkels <adam@sics.se>
 *
 * $Id: uip-split.c,v 1.3 2004/09/12 20:24:56 adamdunkels Exp $
 */

#include "uip-split.h"
#include "uip.h"
#include "uip-fw.h"
#include "uip_arch.h"

#include "tcpip.h"

#define BUF ((uip_tcpip_hdr *)&uip_buf[UIP_LLH_LEN])

/*-----------------------------------------------------------------------------*/
void
uip_split_output(void)
{
  u16_t tcplen, len1, len2;

  /* We only try to split maximum sized TCP segments. */
  if(BUF->proto == UIP_PROTO_TCP &&
     uip_len == UIP_BUFSIZE - UIP_LLH_LEN) {

    tcplen = uip_len - UIP_TCPIP_HLEN;
    /* Split the segment in two. If the original packet length was
       odd, we make the second packet one byte larger. */
    len1 = len2 = tcplen / 2;
    if(len1 + len2 < tcplen) {
      ++len2;
    }

    /* Create the first packet. This is done by altering the length
       field of the IP header and updating the checksums. */
    uip_len = len1 + UIP_TCPIP_HLEN;
    BUF->len[0] = (uip_len >> 8);
    BUF->len[1] = (uip_len & 0xff);
    
    /* Recalculate the TCP checksum. */
    BUF->tcpchksum = 0;
    BUF->tcpchksum = ~(uip_tcpchksum());
    
    /* Recalculate the IP checksum. */
    BUF->ipchksum = 0;
    BUF->ipchksum = ~(uip_ipchksum());

    /* Transmit the first packet. */
    /*    uip_fw_output();*/
    tcpip_output();

    /* Now, create the second packet. To do this, it is not enough to
       just alter the length field, but we must also update the TCP
       sequence number and point the uip_appdata to a new place in
       memory. This place is detemined by the length of the first
       packet (len1). */
    uip_len = len2 + UIP_TCPIP_HLEN;
    BUF->len[0] = (uip_len >> 8);
    BUF->len[1] = (uip_len & 0xff);

    uip_appdata += len1;

    uip_add32(BUF->seqno, len1);
    BUF->seqno[0] = uip_acc32[0];
    BUF->seqno[1] = uip_acc32[1];
    BUF->seqno[2] = uip_acc32[2];
    BUF->seqno[3] = uip_acc32[3];
    
    /* Recalculate the TCP checksum. */
    BUF->tcpchksum = 0;
    BUF->tcpchksum = ~(uip_tcpchksum());
    
    /* Recalculate the IP checksum. */
    BUF->ipchksum = 0;
    BUF->ipchksum = ~(uip_ipchksum());

    /* Transmit the second packet. */
    /*    uip_fw_output();*/
    tcpip_output();
  } else {
    /*    uip_fw_output();*/
    tcpip_output();
  }
     
}
/*-----------------------------------------------------------------------------*/