ICMP.c

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// ////////////////////////////////////////////////////////////////////////////
// ////////////////////////////////////////////////////////////////////////////
/*********************************************************************
 * Software License Agreement
 *
 * Copyright (C) 2002-2008 Microchip Technology Inc.  All rights 
 * reserved.
 *
 * Microchip licenses to you the right to use, modify, copy, and 
 * distribute: 
 * (i)  the Software when embedded on a Microchip microcontroller or 
 *      digital signal controller product ("Device") which is 
 *      integrated into Licensee's product; or
 * (ii) ONLY the Software driver source files ENC28J60.c and 
 *      ENC28J60.h ported to a non-Microchip device used in 
 *      conjunction with a Microchip ethernet controller for the 
 *      sole purpose of interfacing with the ethernet controller. 
 *
 * You should refer to the license agreement accompanying this 
 * Software for additional information regarding your rights and 
 * obligations.
 *
 * THE SOFTWARE AND DOCUMENTATION ARE PROVIDED "AS IS" WITHOUT 
 * WARRANTY OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING WITHOUT 
 * LIMITATION, ANY WARRANTY OF MERCHANTABILITY, FITNESS FOR A 
 * PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT SHALL 
 * MICROCHIP BE LIABLE FOR ANY INCIDENTAL, SPECIAL, INDIRECT OR 
 * CONSEQUENTIAL DAMAGES, LOST PROFITS OR LOST DATA, COST OF 
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 * BY THIRD PARTIES (INCLUDING BUT NOT LIMITED TO ANY DEFENSE 
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 * (INCLUDING NEGLIGENCE), BREACH OF WARRANTY, OR OTHERWISE.
 *
 *
 * Author               Date        Comment
 *~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 * Howard Schlunder     03/16/07    Original
 ********************************************************************/
#define __ICMP_C

#include "TCPIP.h"

/*********************************************************************
 * Function:        void ICMPProcess(void)
 *
 * PreCondition:    MAC buffer contains ICMP type packet.
 *
 * Input:           *remote: Pointer to a NODE_INFO structure of the 
 *                  ping requester
 *                  len: Count of how many bytes the ping header and 
 *                  payload are in this IP packet
 *
 * Output:          Generates an echo reply, if requested
 *                  Validates and sets ICMPFlags.bReplyValid if a 
 *                  correct ping response to one of ours is received.
 *
 * Side Effects:    None
 *
 * Overview:        None
 *
 * Note:            None
 ********************************************************************/
void ICMPProcess(NODE_INFO *remote, WORD len)
{
    DWORD_VAL dwVal;

    // Obtain the ICMP header Type, Code, and Checksum fields
    MACGetArray((BYTE*)&dwVal, sizeof(dwVal));
    
    // See if this is an ICMP echo (ping) request
    if(dwVal.w[0] == 0x0008u)
    {
        // Validate the checksum using the Microchip MAC's DMA module
        // The checksum data includes the precomputed checksum in the 
        // header, so a valid packet will always have a checksum of 
        // 0x0000 if the packet is not disturbed.
        if(MACCalcRxChecksum(0+sizeof(IP_HEADER), len))
            return;
    
        // Calculate new Type, Code, and Checksum values
        dwVal.v[0] = 0x00;  // Type: 0 (ICMP echo/ping reply)
        dwVal.v[2] += 8;    // Subtract 0x0800 from the checksum
        if(dwVal.v[2] < 8u)
        {
            dwVal.v[3]++;
            if(dwVal.v[3] == 0u)
                dwVal.v[2]++;
        }
    
        // Position the write pointer for the next IPPutHeader operation
        MACSetWritePtr(BASE_TX_ADDR + sizeof(ETHER_HEADER));
    
        // Wait for TX hardware to become available (finish transmitting 
        // any previous packet)
        while(!IPIsTxReady());
    
        // Create IP header in TX memory
        IPPutHeader(remote, IP_PROT_ICMP, len);
    
        // Copy ICMP response into the TX memory
        MACPutArray((BYTE*)&dwVal, sizeof(dwVal));
        MACMemCopyAsync(-1, -1, len-4);
        while(!MACIsMemCopyDone());
    
        // Transmit the echo reply packet
        MACFlush();
    }
}

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