UDP Programming

User Datagram Protocol is an alternative way of sending/receive data through the internet without establishing a connection. Unlike TCP, UDP is unreliable because the receiver is not guaranteed to get the data. In addition, out of order packets may occur in the receiver's side.

As a result, UDP is mostly used in video and audio streaming because delayed packets effect the playback quality( i.e. lagging) while dropped packets do not effect the playback quality as much as delayed packets. Another unique UDP's characteristic is the ability to broadcast and multicast to different users.

The Other Day I wrote a program for testing our new W7100 in UDP mode. This program basically sends out a reply message whenever the W7100 receives a UDP message from a UDP client.

There are some considerations when writing this program:

1) How long does the Ethernet negotiation take place?

Currently, I have delayed the program to start after 7 seconds has elapsed

Without this delay, the program will go wild!

2) How much buffer is needed when receiving ?

The buffer string size is the same size as the RX buffer in the W7100 socket.

I hope you enjoyed my article. Enjoy Programming!

Below is the code which I have used to perform this test.

#define MAX_BUF_SIZE 2048 // define maximum buffer size

uint8 xdata pDestaddr[4]; //xdata using external ram

uint16 xdata pPort; // destination port

uint8 xdata rcvLen; // length of data received

uint16 xdata length; // the length of data received

uint8 xdata RXdata[MAX_BUF_SIZE]; // RX data received

uint8 xdata TXData[MAX_BUF_SIZE]; // TX data send

uint16 xdata sentLen; // length of data sent

uint16 xdata TXSize; // size of string sent

Init_iMCU(); // Initialize iMCUW7100

Init_Network(); // Initialize Network Configuration

//Delay for link

wait_1ms(7000);

// 1. create socket for udp

if(socket(0, Sn_MR_UDP,5000, 0) == 1) // create socket with UDP port 5000

{

PutString("\r\n opened socket");

// 2. receive data

while(getSn_RX_RSR(0) == 0) ; // check if there is data in socket

PutString("\r\n got data");

rcvLen = getSn_RX_RSR(0);

if(rcvLen > MAX_BUF_SIZE) // check if data received is bigger than size of buffer string

rcvLen = MAX_BUF_SIZE; // assign max buffer size to the received length

PutString("\r\n RX data size is "); PutITOA(rcvLen); PutString(" Bytes.");

length = recvfrom(0, RXdata, rcvLen, pDestaddr, &pPort); // receive data

PutString("\r\n Received Data");

RXdata[length] = 0; // indicate the end of string

PutString("\r\n RX data : ");

PutString(RXdata); // print received data

// 3. trasnmit data

//set Dest. IP address & Port

pDestaddr[0]= 192;

pDestaddr[1]= 168;

pDestaddr[2]= 1;

pDestaddr[3]= 3;

pPort = 5000;

// Send reply string 'HELLO'

PutString("\r\n TX data size is ");PutITOA(TXSize);

sentLen = sendto(0, TXData, TXSize, pDestaddr, pPort); // transfer data

if (sentLen == TXSize)

PutString("\r\n success to transmit");

else

PutString("\r\n Failed to transmit");

close(0); // close the socket

}

else // if socket is fail

PutString("\r\n Failed to open socket");

while(1);