ble unsubscribe then re-subscribe duplicate packets

I am subscribing to a characteristic and then unsubscribing. If I ever re-subscribe to the characteristic again I get duplicate packets . I need to close matlab in order to stop this issue...

1 connect

app.ble1=ble(app.data1.ble1.address);

2 subscribe and attach funcion (this is in appdesigner..)

app.data1.ble1.readChar = characteristic(app.ble1, ServUUID, CharUUID);
    if(~isempty(app.data1.ble1.readChar.DataAvailableFcn))
        %there is aready a function attached so clear it
        unsubscribe(app.data1.ble1.readChar);
        app.data1.ble1.readDescr = descriptor(app.data1.ble1.readChar,"2902");
        write(app.data1.ble1.readDescr,[00 00]);
        app.data1.ble1.readChar.DataAvailableFcn = [];
    else
        %there is no function attached just but jut incase unsub hard 
        unsubscribe(app.data1.ble1.readChar);
        app.data1.ble1.readDescr = descriptor(app.data1.ble1.readChar,"2902");
        write(app.data1.ble1.readDescr,[00 00]);
    end
    
    write(app.data1.ble1.readDescr,[01 00]);  %write to enable notifications
    app.data1.ble1.readChar.DataAvailableFcn = @(src,evt)BleSubFcn(app,src,evt);
    subscribe(app.data1.ble1.readChar);

3. run the function to print the data

    function BleSubFcn(app,src,~)
    [packet_data,timestamp] = read(src,'oldest');
    if(~isfield(app.data1,'cntr'))
        %this is the first run
        app.data1.cntr=1;
    else
         %packet counting
        app.data1.cntr=app.data1.cntr+1;
    end
    
    flag = uint8(packet_data(1));
    % Get the first bit of the flag, which indicates the format of the heart rate value
    heartRateValueFormat = bitget(flag, 1);
    if heartRateValueFormat == 0
        % Heart rate format is uint8
        heartRate = packet_data(2);
    else
        % Heart rate format is uint16
        heartRate = double(typecast(uint8(packet_data(2:3)), 'uint16'));
    end
    fprintf('HR: %d(bpm), packet: %i , time: %s\n', heartRate, app.data1.cntr,datestr(timestamp,'MM:SS.FFF') );
end

4. shutdown ble

if(~isempty(app.data1.ble1.readChar.DataAvailableFcn))
    %there is aready a function attached to readchar
    unsubscribe(app.data1.ble1.readChar);
    app.data1.ble1.readDescr = descriptor(app.data1.ble1.readChar,"2902");
    write(app.data1.ble1.readDescr,[00 00]);
    app.data1.ble1.readChar.DataAvailableFcn = [];
end
app.ble1=[]; %clear ble connection
app.data1.ble1=[]; %clear stored ble data and charac reads etc

RESULTS

HR: 93(bpm), packet: 241 , time: 03:03.651
HR: 93(bpm), packet: 242 , time: 03:03.652
HR: 94(bpm), packet: 243 , time: 03:04.675
HR: 94(bpm), packet: 244 , time: 03:04.675
HR: 95(bpm), packet: 245 , time: 03:05.650
HR: 95(bpm), packet: 246 , time: 03:05.650
HR: 96(bpm), packet: 247 , time: 03:06.674
HR: 96(bpm), packet: 248 , time: 03:06.674
HR: 97(bpm), packet: 249 , time: 03:07.697
HR: 97(bpm), packet: 250 , time: 03:07.698
HR: 98(bpm), packet: 251 , time: 03:08.672
HR: 98(bpm), packet: 252 , time: 03:08.673
HR: 99(bpm), packet: 253 , time: 03:09.696
HR: 99(bpm), packet: 254 , time: 03:09.696

[Joseph DeCerce]

Also,

Is clearing the ble connection really the only way to close the ble connection? Seems so odd

[Joseph DeCerce]

bump

[Fay Yew]

bump

[Hubert Mathieu]

I have the same issue. I tried a regular subscribre() - unsubscribe() and the method with a callback function, same problem.

Indeed, disconnecting the BLE device is solving the issue, but it shouldn't be the way to do it.

Answer 1

[Jean-Baptiste]

Using Matlab 2024a on Windows 10, I have noticed a duplicate call of the Callback function depending on the order of the operations of setting a callback (setting the field DataAvailableFcn) and subscribing (calling subscribe).

With the following callback:

function cb_read(rx, ev)
s = char(read(rx, 'oldest')); % Fetch the content.
fprintf('%s\n', s); % Display the content.
end

A) When I set the callback first then subscribing, I have duplicate packets (duplicate call of the callback).

oble = ble('112233445566');  % Use the appropriate MAC address.
rx = characteristic(oble, 'SERVICE', 'CHARARCTERISTIC'); % Use the appropriate values.
rx.DataAvailableFcn = @(s, e)cb_read(s, e); % Subscribing.
subscribe(rx); % Setting callback.

B) When I subscribe then setting the callback, I have single packet.

oble = ble('112233445566');  % Use the appropriate MAC address.
rx = characteristic(oble, 'SERVICE', 'CHARARCTERISTIC'); % Use the appropriate values.
subscribe(rx); % Setting callback.
rx.DataAvailableFcn = @(s, e)cb_read(s, e); % Subscribing.

However, in case B), if I unsubscribe and resubscribe, I fall into case A) because a callback is set before calling subscribe()

unsubscribe(rx);
subscribe(rx); % The callback is already set.
% From here the callback is called twice.
%% If I unsubscribe and resubscribe.
unsubscribe(rx);
subscribe(rx); % The callback is already set.
% From Here the callback is called 3 times!