Issue with receiving BLE notifications in Matlab

Hi!

I`m implementing the Matlab class to obtain signal streaming data via BLE from the Nordic MCU.

The signal comes as a Samples with timestamp via notifications to a custom BLE characteristic.

The issue is that Matlab is not reliable when receiving this data (looks like its procesing takes too much time), yet I found that when the notification callback is set as:

obj.mDataChar.DataAvailableFcn = (@(src,event)processNewStreamData(obj,src,event));

the Matlab subsribes to notifications automatically. So, the subsequent call to

subscribe(obj.mDataChar, "notification");

doubles the number of calls to the callback (i.e. if Nordic MCU transmits 10 notifications, Matlab gets around 20 with duplicate data).

In order to make sure I subscribed to this characteristic once, I added a function to check for the active subscription via reading CCCD:

function subscribed = isSubscribedToChar(obj, bleChar)
            % Checks if we are subscribed to the specified BLE
            % characteristic

            subscribed = false;

            % We need to check Client Characteristic Configuration
            % descriptor to check if we are subscribed to the
            % characteristic
            try
                cccd = descriptor(bleChar, "Client Characteristic Configuration");
                attributes = read(cccd);
                subscribed = logical((attributes(1) == 1));
            catch
                warning("Can't check if we are subscribed to char notifications");
            end
        end

Yet this reports active subscription only after

subscribe(obj.mDataChar, "notification");

is called.

So, it leads to the issue of correct data receiving.

I tried with different data rates, but the issue persist.

Normally, Nordic board transmits a single notification with 240 bytes (MTU is 244) with 24ms period.

Can you please suggest if anything is wrong here?

And if there is a way to increase the Matlab callback performance, since the "NRF Connect" app receives the data perfecrly.

Matlab version: R2024a.

Thanks,

Anton

Answer 1

[praguna manvi]

Hi @Anton,

As I see, you are looking to optimize the latency of the callback "processNewStreamData" which processes "ble" notifications. To verify the correctness of your implementation, you can follow the example on using a callback function on "characteristic" object:

openExample('matlab/LogCharDataBLEDeviceCallbackFuncExample')

To fine-tune the performance of your callback function, you can refer to the following link, which details various techniques for improving function performance:

https://www.mathworks.com/help/matlab/matlab_prog/techniques-for-improving-performance.html

Hope this helps!