nRF52840 (BMD-340-A-R) + Raspberry Pi 3B+ max MTU size does not work

[Duy]

Dear Nordic Support,

I am using ble_nus service on nRF52840 (BMD-340-A-R) + Raspberry Pi 3B+ (https://github.com/IanHarvey/bluepy). The nRF52840 is the peripheral and the Pi 3B+ is the central. Using nRF5 SDK 15.3.

I set following parameters:

#define NRF_SDH_BLE_GAP_DATA_LENGTH      251

#define NRF_SDH_BLE_GATT_MAX_MTU_SIZE   247

The connection between the nRF52840 and the Raspberry Pi is OK, the MTU also changed. 

The issue is:

1/ The nRF52840 can only receive and send below 23 bytes.

2/ Same configuration for the nRF52840 but there is not problem when connecting with the Android.

Do you have any suggestion to fix this issue? Or to find the root cause of this? My temporary solution to make the nRF52840 send and receive more than 23 bytes with the Pi 3B+ is modifying the following line in ble_gatt.h:

#define BLE_GATT_ATT_MTU_DEFAULT          23 

change to

#define BLE_GATT_ATT_MTU_DEFAULT          247

I found the relevant case: https://devzone.nordicsemi.com/f/nordic-q-a/38563/max-mtu-for-characteristic-read-not-honoured-in-some-cases

Thank you and best regards,

       Duy Tran

[Simonr]

Hi Duy

Our throughput and long-range demo (and the documentation it links to) might be able to help you understand the MTU process better. As for how to change the MTU size for the Raspberry Pi, I'm not sure how to do this, and I think that question is better suited for a Raspberry Pi forum, as we focus on Nordic products.

Best regards,

Simon

[Duy]

Hello Simonr,

Thank you for your support. I think the document is enough for me. I will take time to play with the throughput and long-range demo.

Best regards,

    Duy