Unwanted L2CAP fragmentation

[QuentinD]

Hello
I am in the process of developing a central BLE and I would like to be able to transmit 240 byte frames with a device.
The problem I have during my tests is that I see that my packets are fragmented into small packets even though the MTU is 247 bytes ...

I have copied the Wireshark log of the communication to you.
2451.Test.pcapng

Do you have any idea what I forgot to stop getting fragmented messages?

Thank you

[Kenneth]

Hi,

You have increased ATT_MTU, but not DLE. So the on-air packet is still limited to 23bytes useful data.

If you are using gatt_init() then this should be handled for you, though you can take a look at the ble_app_uart examples which I believe is doing this also. For more info also check out this blog post by third party:
https://www.novelbits.io/bluetooth-5-speed-maximum-throughput/

Kenneth

[QuentinD]

Hi

In fact, it was not in my gatt_init () that there was a problem: the problem came from my "#define NRF_SDH_BLE_GAP_DATA_LENGTH" which was at 27 instead of 251

Now it works.
Thank you