MTU exchange procedure

[alemv]

When the macro NRF_SDH_BLE_GATT_MAX_MTU_SIZE is changed in the sdk_config.h file of any example from the ble_peripheral folder, the slave sends the message Exchange MTU Request (ATT_EXCHANGE_MTU_REQ) immediately after the connect event.
Is it correct?
As I understand, the ATT_EXCHANGE_MTU_REQ request shall only be sent once during a connection by the ATT client (the master).
Am I missing something?

nRF52840
nRF5_SDK_16.0.0_98a08e2
s140_nrf52_7.0.1_softdevice.hex

[alemv]

In my opinion, your interpretation of the "The ATT_EXCHANGE_MTU_REQ PDU is used by the client to inform the server" as "the paragraph does not explicitly prohibit the server from doing the same" is very controversial.
Because:
1. The ATT_EXCHANGE_MTU_REQ PDU has "Client Rx MTU" parameter, not "Rx MTU" or "Server Rx MTU";
2. If the GATT server sends the MTU request, it may cause problems:
- with Windows 10, see this message
- with Linux (Python + BluePY + Bluez), see this thread

So, in my opinion, the modifying on_connected_evt() function in nrf_ble_gatt.c like in this message is not a good alternative. A preprocessor macro or other choice for a programmer would be better.

Anyway, thank you for your time and clarification of your position.

[Amanda Hsieh]

Thanks for your feedback. I will report to the internal.

-Amanda H.