TCP/IP Callback Function Not Being Triggered Unless a BreakPoint is Placed In Callback Function.

I have a script that connects two locally networked machines via TCP/IP. The goal is to send information from one to the other. I wrote a simple script to test my understanding of the process, and am getting weird results.

Essentially, my BytesAvailableFcn callback is ONLY being called if I have an active breakpoint in it - otherwise, the callback is ignored.

My test script is:

t = tcpip(IP_Address,PortNumber,'NetworkRole','client')
t.BytesAvailableFcnMode = 'byte'
t.BytesAvailableFcn = @(a,b) RXDATA(a,b,t);
fopen(t)

function [data] = RXDATA(obj, EventData, t)
try
    fprintf('I AM HERE!\n')
    data.clock = EventData.Data.AbsTime;
    data.Value = fscanf(t,'%s');
    disp(data)
    assignin('base','data',data)
catch
    fprintf('I BROKE!\n');
end
end

I do not believe there to be any problems on the server side, as I am able to manually use fscanf in the command line to pull the sent data. I am also able to see that "BytesAvailable" in t is non zero.

The only difference between when this callback works and when it doesn't seems to be when a breakpoint is placed in the callback. I haven't experienced a breakpoint changing the operation of a function before, so any insight would be greatly appreciated.

Answer 1

[Sourav Ghai]

Hi,

First you need to specify the value for 'BytesAvailableFcnCount'.

For example:

t.BytesAvailableFcnMode = 'byte'
t.BytesAvailableFcnCount = 5;

This basically means that the moment input buffer will have 5 bytes of data, the 'BytesAvailableFcn' callback function will get triggered.

Code for client side:

IP_Address = 'localhost';
PortNumber = 30000;

t = tcpip(IP_Address,PortNumber,'NetworkRole','client')
t.BytesAvailableFcnCount = 5;
t.BytesAvailableFcnMode = 'byte'
t.BytesAvailableFcn = @(a,b) RXDATA(a,b,t);
fopen(t);
function [data] = RXDATA(obj, EventData, t)
try
    disp('1234')
    data.clock = EventData.Data.AbsTime;
    data.Value = 1:25;
    disp(data)
    assignin('base','data',data)
catch
     fprintf('6789\n');
end
end

Code for server side:

t = tcpip('0.0.0.0', 30000, 'NetworkRole', 'server');
fopen(t);
data = 1:20;
fwrite(t,data);
fclose(t);
delete(t);
clear t;

For more infromation you can refer https://www.mathworks.com/help/instrument/bytesavailablefcn.html.