/*,-----------------------------------------------------------------------------------------.| net/icmp|-----------------------------------------------------------------------------------------| this file implements a very basic icmp protocol| - ethernet packet generation is done| - received ping request is answered with reply| - thats it! we can not send a ping request for example...|| Author   : {{removed according to contest rules}}|            -> circuitcellar.com avr design contest 2006|            -> Entry #AT2616||-----------------------------------------------------------------------------------------| License:| This program is free software; you can redistribute it and/or modify it under| the terms of the GNU 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 General Public License for more details.|| You should have received a copy of the GNU General Public License along with| this program; if not, write to the Free Software Foundation, Inc., 51| Franklin St, Fifth Floor, Boston, MA 02110, USA|| http://www.gnu.de/gpl-ger.html`-----------------------------------------------------------------------------------------*/#include "icmp.h"#include "mynic.h"#include "ip.h"//ACTIVATE DEBUG by editing this file:#include "debug.h"//called if icmp packet comes invoid icmp_packet_in(unsigned char *buffer,unsigned int len){	int i;	int pos;	//we only support ICMP echo request (ping) packets:	if (buffer[ICMP_POS_TYPE] == ICMP_TYPE_ECHO_REQUEST){		#if ICMP_DEBUG		softuart_puts_progmem("ICMP: echo reply sent");		softuart_putnewline();		#endif		//reuse buffer for the ICMP echo reply:		//*******************************		//setup the eth packet:		//get packet target mac from arp table:		pos = arp_search_by_ip(nic_buffer_to_ip(&buffer[IP_POS_SRC_IP]));		if (pos<0){			//no match, copy src to target ...			for(i=0; i<6; i++)				buffer[i] = buffer[6+i];		}else{			//match, copy mac from arp table:			for(i=0; i<6; i++)				buffer[i] = arp_table[pos].mac[i];		}		//packet source mac:		nic_copy_mac_to_buf(&buffer[6]);		//change type to ECHO REPLY		buffer[ICMP_POS_TYPE] = ICMP_TYPE_ECHO_REPLY;				//"calculate" checksum:		//use quick & dirty hack, we change only the icmp type		//so we can calculate the new checksum like this:		if (buffer[ICMP_POS_CHECKSUM+0] > 0xFF-0x08)			buffer[ICMP_POS_CHECKSUM+1] = buffer[ICMP_POS_CHECKSUM+1] + 1;		buffer[ICMP_POS_CHECKSUM+0] = buffer[ICMP_POS_CHECKSUM+0] + 0x08;		//set up dst ip (copy src to dest ip):		for(i=0; i<4; i++){			buffer[IP_POS_DST_IP+i] = buffer[IP_POS_SRC_IP+i];		}				//set up src ip:		nic_ip_to_buffer(&buffer[IP_POS_SRC_IP], nic_ip);				nic_send_packet(buffer,len);	}}