BLE_EVT_USER_MEM_REQUEST if data_length is > 180 bytes on iOS but not for Android

[Constantin]

Hi,

we user the standard NUS example as peripheral. Starting from IPhone 7 an mtu size of 251 is negotiated. Sending from the peripheral is possible but receiving from the IPhone bigger than 18ß bytes results in BLE_EVT_USER_MEM_REQUEST and then BLE_GATTS_EVT_RW_AUTHORIZE_REQUEST which with the standard code of the nus example gives an NRF_ERROR_INVALID_STATE. This could be solved with  https://devzone.nordicsemi.com/f/nordic-q-a/22718/invalid_param-for-sd_ble_gatts_rw_authorize_reply/205199#205199.But still I could not receive the long package. Funny thing is, that with android it is working. I can receive payloads up 251 bytes.

Is there any particular reason for this?

Best regards,

C.W.

[Constantin]

Solved the solution can be found here: 

https://devzone.nordicsemi.com/f/nordic-q-a/44825/ios-mtu-size-why-only-185-bytes

It is because I initially asked for MTU exchange which is then answered with a 182 bytes MTU. Then afterwards I renegotiate the MTU but iOS still thinks it is only 182 for sending. Hence it askes for concatenating the packages with BLE_EVT_USER_MEM_REQUEST.