how to get visa BytesAvailable buffering?

With the old visa function, what is required from the device for matlab to buffer data in the background (e.g. BytesAvailable property)? I have a USB-raw device that i'm attempting to program minimal firmware functionality into to stream data continuously to matlab. currently it sends data, and matlab receives it only when performing fread. it's not buffering in the background.

Answer 1

[Shantanu Dixit]

Hi George,

If I understood your query correctly, you want MATLAB to buffer data in the background using the 'visa' object so that data is available in 'BytesAvailable' property of the object.

Based on the documentation: https://in.mathworks.com/help/instrument/visa.html, 'visa' object does buffer incoming data, but the 'BytesAvailable' property can be used only when the data is read asynchronously https://in.mathworks.com/help/instrument/visa.html#mw_aaeffe24-c03c-434f-8b87-6b224dd932d3.

You can enable the background buffering by using asynchronous reading, 'ReadAsyncMode'(set to continuous by default) and setting up a callback function ('BytesAvailableFcn'). This function will automatically trigger when a specified number of bytes are available ('BytesAvailableFcnCount') or a terminator is read.

% visaObj: visa object
visaObj.BytesAvailableFcnMode = 'byte';           
visaObj.BytesAvailableFcnCount = 64;              % set to sufficiently large value (based on data)
visaObj.BytesAvailableFcn = @myCallbackFunction;  % callback 

function myCallbackFunction(obj, ~)
    % logic to read the available data     
end

Hope this helps!