/*********************************************
* vim:sw=8:ts=8:si:et
* To use the above modeline in vim you must have "set modeline" in your .vimrc
*
* Author: Guido Socher
* Copyright: GPL V2
* See http://www.gnu.org/licenses/gpl.html
*
* IP, Arp, UDP and TCP functions.
*
* The TCP implementation uses some size optimisations which are valid
* only if all data can be sent in one single packet. This is however
* not a big limitation for a microcontroller as you will anyhow use
* small web-pages. The TCP stack is therefore a SDP-TCP stack (single data packet TCP).
*
* Chip type : ATMEGA88 with ENC28J60
*********************************************/
#include <avr/io.h>
#include <avr/pgmspace.h>
#include "avr_compat.h"
#include "net.h"
#include "enc28j60.h"
static uint8_t wwwport=80;
static uint8_t macaddr[6];
static uint8_t ipaddr[4];
static int16_t info_hdr_len=0;
static int16_t info_data_len=0;
static uint8_t seqnum=0xa; // my initial tcp sequence number
// The Ip checksum is calculated over the ip header only starting
// with the header length field and a total length of 20 bytes
// unitl ip.dst
// You must set the IP checksum field to zero before you start
// the calculation.
// len for ip is 20.
//
// For UDP/TCP we do not make up the required pseudo header. Instead we
// use the ip.src and ip.dst fields of the real packet:
// The udp checksum calculation starts with the ip.src field
// Ip.src=4bytes,Ip.dst=4 bytes,Udp header=8bytes + data length=16+len
// In other words the len here is 8 + length over which you actually
// want to calculate the checksum.
// You must set the checksum field to zero before you start
// the calculation.
// len for udp is: 8 + 8 + data length
// len for tcp is: 4+4 + 20 + option len + data length
//
// For more information on how this algorithm works see:
// http://www.netfor2.com/checksum.html
// http://www.msc.uky.edu/ken/cs471/notes/chap3.htm
// The RFC has also a C code example: http://www.faqs.org/rfcs/rfc1071.html
uint16_t checksum(uint8_t *buf, uint16_t len,uint8_t type){
// type 0=ip
// 1=udp
// 2=tcp
uint32_t sum = 0;
//if(type==0){
// // do not add anything
//}
if(type==1){
sum+=IP_PROTO_UDP_V; // protocol udp
// the length here is the length of udp (data+header len)
// =length given to this function - (IP.scr+IP.dst length)
sum+=len-8; // = real tcp len
}
if(type==2){
sum+=IP_PROTO_TCP_V;
// the length here is the length of tcp (data+header len)
// =length given to this function - (IP.scr+IP.dst length)
sum+=len-8; // = real tcp len
}
// build the sum of 16bit words
while(len >1){
sum += 0xFFFF & (*buf<<8|*(buf+1));
buf+=2;
len-=2;
}
// if there is a byte left then add it (padded with zero)
if (len){
sum += (0xFF & *buf)<<8;
}
// now calculate the sum over the bytes in the sum
// until the result is only 16bit long
while (sum>>16){
sum = (sum & 0xFFFF)+(sum >> 16);
}
// build 1's complement:
return( (uint16_t) sum ^ 0xFFFF);
}
// you must call this function once before you use any of the other functions:
void init_ip_arp_udp_tcp(uint8_t *mymac,uint8_t *myip,uint8_t wwwp){
uint8_t i=0;
wwwport=wwwp;
while(i<4){
ipaddr[i]=myip[i];
i++;
}
i=0;
while(i<6){
macaddr[i]=mymac[i];
i++;
}
}
uint8_t eth_type_is_arp_and_my_ip(uint8_t *buf,uint16_t len){
uint8_t i=0;
//
if (len<41){
return(0);
}
if(buf[ETH_TYPE_H_P] != ETHTYPE_ARP_H_V ||
buf[ETH_TYPE_L_P] != ETHTYPE_ARP_L_V){
return(0);
}
while(i<4){
if(buf[ETH_ARP_DST_IP_P+i] != ipaddr[i]){
return(0);
}
i++;
}
return(1);
}
uint8_t eth_type_is_ip_and_my_ip(uint8_t *buf,uint16_t len){
uint8_t i=0;
//eth+ip+udp header is 42
if (len<42){
return(0);
}
if(buf[ETH_TYPE_H_P]!=ETHTYPE_IP_H_V ||
buf[ETH_TYPE_L_P]!=ETHTYPE_IP_L_V){
return(0);
}
if (buf[IP_HEADER_LEN_VER_P]!=0x45){
// must be IP V4 and 20 byte header
return(0);
}
while(i<4){
if(buf[IP_DST_P+i]!=ipaddr[i]){
return(0);
}
i++;
}
return(1);
}
// make a return eth header from a received eth packet
void make_eth(uint8_t *buf)
{
uint8_t i=0;
//
//copy the destination mac from the source and fill my mac into src
while(i<6){
buf[ETH_DST_MAC +i]=buf[ETH_SRC_MAC +i];
buf[ETH_SRC_MAC +i]=macaddr[i];
i++;
}
}
void fill_ip_hdr_checksum(uint8_t *buf)
{
uint16_t ck;
// clear the 2 byte checksum
buf[IP_CHECKSUM_P]=0;
buf[IP_CHECKSUM_P+1]=0;
buf[IP_FLAGS_P]=0x40; // don't fragment
buf[IP_FLAGS_P+1]=0; // fragement offset
buf[IP_TTL_P]=64; // ttl
// calculate the checksum:
ck=checksum(&buf[IP_P], IP_HEADER_LEN,0);
buf[IP_CHECKSUM_P]=ck>>8;
buf[IP_CHECKSUM_P+1]=ck& 0xff;
}
// make a return ip header from a received ip packet
void make_ip(uint8_t *buf)
{
uint8_t i=0;
while(i<4){
buf[IP_DST_P+i]=buf[IP_SRC_P+i];
buf[IP_SRC_P+i]=ipaddr[i];
i++;
}
fill_ip_hdr_checksum(buf);
}
// make a return tcp header from a received tcp packet
// rel_ack_num is how much we must step the seq number received from the
// other side. We do not send more than 255 bytes of text (=data) in the tcp packet.
// If mss=1 then mss is included in the options list
//
// After calling this function you can fill in the first data byte at TCP_OPTIONS_P+4
// If cp_seq=0 then an initial sequence number is used (should be use in synack)
// otherwise it is copied from the packet we received
void make_tcphead(uint8_t *buf,uint16_t rel_ack_num,uint8_t mss,uint8_t cp_seq)
{
uint8_t i=0;
uint8_t tseq;
while(i<2){
buf[TCP_DST_PORT_H_P+i]=buf[TCP_SRC_PORT_H_P+i];
buf[TCP_SRC_PORT_H_P+i]=0; // clear source port
i++;
}
// set source port (http):
buf[TCP_SRC_PORT_L_P]=wwwport;
i=4;
// sequence numbers:
// add the rel ack num to SEQACK
while(i>0){
rel_ack_num=buf[TCP_SEQ_H_P+i-1]+rel_ack_num;
tseq=buf[TCP_SEQACK_H_P+i-1];
buf[TCP_SEQACK_H_P+i-1]=0xff&rel_ack_num;
if (cp_seq){
// copy the acknum sent to us into the sequence number
buf[TCP_SEQ_H_P+i-1]=tseq;
}else{
buf[TCP_SEQ_H_P+i-1]= 0; // some preset vallue
}
rel_ack_num=rel_ack_num>>8;
i--;
}
if (cp_seq==0){
// put inital seq number
buf[TCP_SEQ_H_P+0]= 0;
buf[TCP_SEQ_H_P+1]= 0;
// we step only the second byte, this allows us to send packts
// with 255 bytes or 512 (if we step the initial seqnum by 2)
buf[TCP_SEQ_H_P+2]= seqnum;
buf[TCP_SEQ_H_P+3]= 0;
// step the inititial seq num by something we will not use
// during this tcp session:
seqnum+=2;
}
// 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 */