MATLAB - transfer variables between callback and main program without guidata

Question

I am setting up a serial communication in matlab without GUI.

The serial initialisation looks like this (main program):

handles.s = serial('COM10' ,'BaudRate', 9600);
    set(handles.s,'Terminator','CR');
    set(handles.s,'Timeout',1);
    set(handles.s, 'BytesAvailableFcnMode', 'byte');
    set(handles.s, 'BytesAvailableFcnCount', 1);
    set(handles.s, 'BytesAvailableFcn', {@serialEventHandler, handles});
fopen(handles.s);

I am reading the buffer with a callback function (serialEventHandler)

function serialEventHandler(serialConnection, ~, handles)
    bytes = get(serialConnection, 'BytesAvailable');
    if(bytes > 0 ) % we may have alread read the data
        handles.data = fscanf(serialConnection)
        % fwrite(handles.appenderFile, handles.data); (not relevant here)
    end
end

For some reason, the callback does not update my handles structure and I am unable to access the serial data the main code. I understand this is the role of guidata(hobject, handles) in a GUI application, but is there a way to do this without GUI? Many thanks,

gnovice · Accepted Answer · 2017-06-22 16:20:29Z

You'll want to take a look at the documentation for Sharing Data Between Workspaces. Two of the options there should work for you, depending on where serialEventHandler is with respect to your main code:

For functions in separate files: You will need to use global variables to share your handles structure between them. In your main program:

global handles
%... Initialize handles ...
set(handles.s, 'BytesAvailableFcn', @serialEventHandler);  % Don't have to pass it

And in serialEventHandler:

function serialEventHandler(serialConnection, ~)  % Don't have to pass it
  global handles
  %... Rest of code ...
end

For functions in the same file: You can nest one function inside the other, allowing them to share access to variables without having to pass them as input or output arguments:

function main

  %... Initialize handles ...
  set(handles.s, 'BytesAvailableFcn', @serialEventHandler);  % Don't have to pass it
  %... Rest of main code ...

  function serialEventHandler(serialConnection, ~)  % Don't have to pass it
    %... serialEventHandler code ...
  end

end

There is a third option as well (not mentioned in the above documentation on sharing data), but it could be substantially more work to implement: Creating your own class to use in place of your handles structure and deriving from the handle class to give it reference-like (i.e. pointer-like) behavior. Although creating a new class would be more involved, it would allow you to pass your handles object to any function without having to return a modified version. Your code above would likely remain unchanged.

Vahe Tshitoyan · Accepted Answer · 2017-06-22 17:42:25Z

0

As an alternative method to the ones well described by @gnovice, you could always write the variable contents to a file and read them in other parts of code.

answered Jun 22, 2017 at 17:42

Vahe Tshitoyan

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