Receiving UDP data from Arduino

I am trying to send a string from my Arduino to Matlab using Ethernet. Sending from Matlab to the Arduino board is no problem using UDP and I have successful communication both ways using Processing instead of Matlab (also UDP).

I simply can't seem to read the UDP object. I'm sure the object is sent as the Processing application can read it.

For the most basic example, here is the code in Matlab:

remPort=8888;      
host='10.0.0.177';  
locPort=9055;
u = udp(host,'RemotePort',remPort,'LocalPort',locPort); 

fopen(u)

A = fread(u);

fclose(u)

And on the Arduino:

#include <SPI.h>
#include <Ethernet.h>
#include <EthernetUdp.h>

byte mac[] = { 0x90, 0xA2, 0xDA, 0x0D, 0xFF, 0xA0 };  

byte ip[] = { 10, 0, 0, 177 };    

unsigned int localPort = 8888;  

EthernetUDP Udp;

void setup()
{
  Ethernet.begin(mac, ip);

    Udp.begin(localPort);
  }

void loop () {

    Udp.beginPacket(Udp.remoteIP(), Udp.remotePort());

    Udp.write("Hi");

    delay(50);

    Udp.endPacket();

}

I get this warning:

Warning: Unsuccessful read: The specified amount of data was not returned within the Timeout period.

When using fread(u,'BytesAvailable') i get 0.

Any ideas?

Edit:

I have made further tests using serial connection, works like a charm both ways. The serial object seems very similar to the UDP object:

>> a

     Serial Port Object : Serial-COM3

     Communication Settings 
        Port:               COM3
        BaudRate:           9600
        Terminator:         'LF'

     Communication State 
        Status:             closed
        RecordStatus:       off

     Read/Write State  
        TransferStatus:     idle
        BytesAvailable:     0
        ValuesReceived:     5
        ValuesSent:         0

>> u

     UDP Object : UDP-10.0.0.177

     Communication Settings 
        RemotePort:         8888
        RemoteHost:         10.0.0.177
        Terminator:         'LF'

     Communication State 
        Status:             closed
        RecordStatus:       off

     Read/Write State  
        TransferStatus:     idle
        BytesAvailable:     0
        ValuesReceived:     0
        ValuesSent:         0

As you see, data has been received only using serial.

Tried using fscanf instead of fread and to specify a string beeing reveived as fscanf(u,'%s'), but doesn't work for UDP. I get new warning:

Warning: Unsuccessful read: A timeout occurred before the Terminator was reached.

Strange since the serial and UDP have the same terminator.

Answer 1

[Martin]

SOLVED

After many hours of pulling my hair it turns out it was the firewall blocking the port :-/

Somehow the Processing application could read it anyway.

Used fscanf for strings and fread for others.

[shubhum awarchar]

how did u solved the problem of port

Answer 2

[Nathan Crosty]

One thing I can tell you is that your endianness will be opposite between the Arduino and Matlab. Other than that, your paremeters for BeginPacket are different than how I use them. Here is a copy paste of some working example code.

Setup (Run this once):

    byte mac[] = {
    0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
    Serial.begin(9600);
    Eth.begin(mac);
    Udp.begin(8888);

Loop:

    IPAddress sendTo(192,168,1,80);
    int remotePort = 8885;

    Udp.beginPacket(sendTo, remotePort);
    Udp.write("hello");
    Udp.endPacket();

    /*...delay...*/

[Martin]

Our code for the Arduino is the same, including the parameterization.

Are you sending to a Matlab application? What code do you use?

I'm not familiar with endianness issues, but isn't it strange that I can send a string from Matlab to Arduino (and it beening interpreted correctly) but not the other way?

[Nathan Crosty]

I just noticed that you are not being specific enough with your fread in Matlab. You need to specify a buffer size and a type, etc. for this to work. Check out the documentation for fread.