ip_arp_udp_tcp.c

C++ source code for accesing serial memory chip with atmega16 microcontroler.

        }
        // zero the checksum
        buf[TCP_CHECKSUM_H_P]=0;
        buf[TCP_CHECKSUM_L_P]=0;

        // The tcp header length is only a 4 bit field (the upper 4 bits).
        // It is calculated in units of 4 bytes. 
        // E.g 24 bytes: 24/4=6 => 0x60=header len field
        //buf[TCP_HEADER_LEN_P]=(((TCP_HEADER_LEN_PLAIN+4)/4)) <<4; // 0x60
        if (mss){
                // the only option we set is MSS to 1408:
                // 1408 in hex is 0x580
                buf[TCP_OPTIONS_P]=2;
                buf[TCP_OPTIONS_P+1]=4;
                buf[TCP_OPTIONS_P+2]=0x05; 
                buf[TCP_OPTIONS_P+3]=0x80;
                // 24 bytes:
                buf[TCP_HEADER_LEN_P]=0x60;
        }else{
                // no options:
                // 20 bytes:
                buf[TCP_HEADER_LEN_P]=0x50;
        }
}

void make_arp_answer_from_request(uint8_t *buf)
{
        uint8_t i=0;
        //
        make_eth(buf);
        buf[ETH_ARP_OPCODE_H_P]=ETH_ARP_OPCODE_REPLY_H_V;
        buf[ETH_ARP_OPCODE_L_P]=ETH_ARP_OPCODE_REPLY_L_V;
        // fill the mac addresses:
        while(i<6){
                buf[ETH_ARP_DST_MAC_P+i]=buf[ETH_ARP_SRC_MAC_P+i];
                buf[ETH_ARP_SRC_MAC_P+i]=macaddr[i];
                i++;
        }
        i=0;
        while(i<4){
                buf[ETH_ARP_DST_IP_P+i]=buf[ETH_ARP_SRC_IP_P+i];
                buf[ETH_ARP_SRC_IP_P+i]=ipaddr[i];
                i++;
        }
        // eth+arp is 42 bytes:
        enc28j60PacketSend(42,buf); 
}

void make_echo_reply_from_request(uint8_t *buf,uint16_t len)
{
        make_eth(buf);
        make_ip(buf);
        buf[ICMP_TYPE_P]=ICMP_TYPE_ECHOREPLY_V;
        // we changed only the icmp.type field from request(=8) to reply(=0).
        // we can therefore easily correct the checksum:
        if (buf[ICMP_CHECKSUM_P] > (0xff-0x08)){
                buf[ICMP_CHECKSUM_P+1]++;
        }
        buf[ICMP_CHECKSUM_P]+=0x08;
        //
        enc28j60PacketSend(len,buf);
}

// you can send a max of 220 bytes of data
/*
void make_udp_reply_from_request(uint8_t *buf,char *data,uint8_t datalen,uint16_t port)
{
        uint8_t i=0;
        uint16_t ck;
        make_eth(buf);
        if (datalen>220){
                datalen=220;
        }
        // total length field in the IP header must be set:
        buf[IP_TOTLEN_H_P]=0;
        buf[IP_TOTLEN_L_P]=IP_HEADER_LEN+UDP_HEADER_LEN+datalen;
        make_ip(buf);
        buf[UDP_DST_PORT_H_P]=port>>8;
        buf[UDP_DST_PORT_L_P]=port & 0xff;
        // source port does not matter and is what the sender used.
        // calculte the udp length:
        buf[UDP_LEN_H_P]=0;
        buf[UDP_LEN_L_P]=UDP_HEADER_LEN+datalen;
        // zero the checksum
        buf[UDP_CHECKSUM_H_P]=0;
        buf[UDP_CHECKSUM_L_P]=0;
        // copy the data:
        while(i<datalen){
                buf[UDP_DATA_P+i]=data[i];
                i++;
        }
        ck=checksum(&buf[IP_SRC_P], 16 + datalen,1);
        buf[UDP_CHECKSUM_H_P]=ck>>8;
        buf[UDP_CHECKSUM_L_P]=ck& 0xff;
        enc28j60PacketSend(UDP_HEADER_LEN+IP_HEADER_LEN+ETH_HEADER_LEN+datalen,buf);
}
*/
void make_tcp_synack_from_syn(uint8_t *buf)
{
        uint16_t ck;
        make_eth(buf);
        // total length field in the IP header must be set:
        // 20 bytes IP + 24 bytes (20tcp+4tcp options)
        buf[IP_TOTLEN_H_P]=0;
        buf[IP_TOTLEN_L_P]=IP_HEADER_LEN+TCP_HEADER_LEN_PLAIN+4;
        make_ip(buf);
        buf[TCP_FLAGS_P]=TCP_FLAGS_SYNACK_V;
        make_tcphead(buf,1,1,0);
        // calculate the checksum, len=8 (start from ip.src) + TCP_HEADER_LEN_PLAIN + 4 (one option: mss)
        ck=checksum(&buf[IP_SRC_P], 8+TCP_HEADER_LEN_PLAIN+4,2);
        buf[TCP_CHECKSUM_H_P]=ck>>8;
        buf[TCP_CHECKSUM_L_P]=ck& 0xff;
        // add 4 for option mss:
        enc28j60PacketSend(IP_HEADER_LEN+TCP_HEADER_LEN_PLAIN+4+ETH_HEADER_LEN,buf);
}

// get a pointer to the start of tcp data in buf
// Returns 0 if there is no data
// You must call init_len_info once before calling this function
uint16_t get_tcp_data_pointer(void)
{
        if (info_data_len){
                return((uint16_t)TCP_SRC_PORT_H_P+info_hdr_len);
        }else{
                return(0);
        }
}

// do some basic length calculations and store the result in static varibales
void init_len_info(uint8_t *buf)
{
        info_data_len=(buf[IP_TOTLEN_H_P]<<8)|(buf[IP_TOTLEN_L_P]&0xff);
        info_data_len-=IP_HEADER_LEN;
        info_hdr_len=(buf[TCP_HEADER_LEN_P]>>4)*4; // generate len in bytes;
        info_data_len-=info_hdr_len;
        if (info_data_len<=0){
                info_data_len=0;
        }
}

// fill in tcp data at position pos. pos=0 means start of
// tcp data. Returns the position at which the string after
// this string could be filled.
uint16_t fill_tcp_data_p(uint8_t *buf,uint16_t pos, const prog_char *progmem_s)
{
        char c;
        // fill in tcp data at position pos
        //
        // with no options the data starts after the checksum + 2 more bytes (urgent ptr)
        while ((c = pgm_read_byte(progmem_s++))) {
                buf[TCP_CHECKSUM_L_P+3+pos]=c;
                pos++;
        }
        return(pos);
}

// fill in tcp data at position pos. pos=0 means start of
// tcp data. Returns the position at which the string after
// this string could be filled.
uint16_t fill_tcp_data(uint8_t *buf,uint16_t pos, const char *s)
{
        // fill in tcp data at position pos
        //
        // with no options the data starts after the checksum + 2 more bytes (urgent ptr)
        while (*s) {
                buf[TCP_CHECKSUM_L_P+3+pos]=*s;
                pos++;
                s++;
        }
        return(pos);
}

// Make just an ack packet with no tcp data inside
// This will modify the eth/ip/tcp header 
void make_tcp_ack_from_any(uint8_t *buf)
{
        uint16_t j;
        make_eth(buf);
        // fill the header:
        buf[TCP_FLAGS_P]=TCP_FLAGS_ACK_V;
        if (info_data_len==0){
                // if there is no data then we must still acknoledge one packet
                make_tcphead(buf,1,0,1); // no options
        }else{
                make_tcphead(buf,info_data_len,0,1); // no options
        }

        // total length field in the IP header must be set:
        // 20 bytes IP + 20 bytes tcp (when no options) 
        j=IP_HEADER_LEN+TCP_HEADER_LEN_PLAIN;
        buf[IP_TOTLEN_H_P]=j>>8;
        buf[IP_TOTLEN_L_P]=j& 0xff;
        make_ip(buf);
        // calculate the checksum, len=8 (start from ip.src) + TCP_HEADER_LEN_PLAIN + data len
        j=checksum(&buf[IP_SRC_P], 8+TCP_HEADER_LEN_PLAIN,2);
        buf[TCP_CHECKSUM_H_P]=j>>8;
        buf[TCP_CHECKSUM_L_P]=j& 0xff;
        enc28j60PacketSend(IP_HEADER_LEN+TCP_HEADER_LEN_PLAIN+ETH_HEADER_LEN,buf);
}

// you must have called init_len_info at some time before calling this function
// dlen is the amount of tcp data (http data) we send in this packet
// You can use this function only immediately after make_tcp_ack_from_any
// This is because this function will NOT modify the eth/ip/tcp header except for
// length and checksum
void make_tcp_ack_with_data(uint8_t *buf,uint16_t dlen)
{
        uint16_t j;
        // fill the header:
        // This code requires that we send only one data packet
        // because we keep no state information. We must therefore set
        // the fin here:
        buf[TCP_FLAGS_P]=TCP_FLAGS_ACK_V|TCP_FLAGS_PUSH_V|TCP_FLAGS_FIN_V;

        // total length field in the IP header must be set:
        // 20 bytes IP + 20 bytes tcp (when no options) + len of data
        j=IP_HEADER_LEN+TCP_HEADER_LEN_PLAIN+dlen;
        buf[IP_TOTLEN_H_P]=j>>8;
        buf[IP_TOTLEN_L_P]=j& 0xff;
        fill_ip_hdr_checksum(buf);
        // zero the checksum
        buf[TCP_CHECKSUM_H_P]=0;
        buf[TCP_CHECKSUM_L_P]=0;
        // calculate the checksum, len=8 (start from ip.src) + TCP_HEADER_LEN_PLAIN + data len
        j=checksum(&buf[IP_SRC_P], 8+TCP_HEADER_LEN_PLAIN+dlen,2);
        buf[TCP_CHECKSUM_H_P]=j>>8;
        buf[TCP_CHECKSUM_L_P]=j& 0xff;
        enc28j60PacketSend(IP_HEADER_LEN+TCP_HEADER_LEN_PLAIN+dlen+ETH_HEADER_LEN,buf);
}

/* end of ip_arp_udp.c */