How is nrfConnect android app able to send more than 20 bytes from android app to raspberrypi?

[Tharun]

Hi,

I am trying to write a 120 byte data through ble to raspberrypi from my android app(I increased the MTU to the required limit). But all I am able to transfer is first 20 bytes. When I tried to search on the internet, I see that android limits the size to 20 byte for ble transfers and I will have to send multiple 20 byte packets.

But why I tried to end the same data from nrfConnect android app, I see that the data is being transferred without any issue. Can you help me understand how nrfConnect is able to do it with you writing it as packets?

I tried to use reliableWrite(below). But even that has sent on 20 bytes.

            gatt.beginReliableWrite();
            gatt.writeCharacteristic(characteristic);
            return gatt.executeReliableWrite();

[Tharun]

I guess the way I am trying to use beginReliableWrite is wrong. But the main question still remains as to how nrfConnect is able to send the data and why is my app not able to send it. 

Just as info, I am able to send 52 bytes to our custom board with nrf52 chip from the same app.

[Tharun]

Found a solution.

Even though we increased the limit in raspberrypi, for some reason only when I add requestMtu() call to add the number of byte, the entire data is going through. I didn't need to do this when I was writing 50 bytes to a nrf51 chip.