topic Re: How to increase MAX ATT_MTU size ? in Wireless MCU

How to increase MAX ATT_MTU size ?

rajarathinamlaw — Wed, 14 Mar 2018 22:45:17 GMT

I am using FRDM KW40z dev.board and KW40Z_Connectivity_Software_1.0.1 software for our application development. Here I need increase ATT_MTU size as 512 byte instead of 23(gAttMaxMtu_c = 23) for application but I changed gAttMaxMtu_c as 512 in ble_constants.h file and after connection application called GattClient_ExchangeMtu(peerDeviceId) function but still MTU exchanged with client RX MTU size is 23.

Could you please explain how to increase the ATT_MTU maximum size to upload large data?

Re: How to increase MAX ATT_MTU size ?

neoxiong — Sun, 18 Mar 2018 03:04:25 GMT

Hi, Raja

You are not able to change macro in ble_constants.h file as they're hard linked by nxp ble stack. I think whatever the value you modify, the stack still uses 23.

KW40 is a BLE 4.1 SoC which only support short packet, even you set ATT_MTU to 512, on l2cap level, stack will split it into multiple link layer packets, throughput will get not significant improve (only few bytes overhead get reduced).

And, KW40 is an old device, could you consider switching to KW41? KW41 is BLE 4.2 SoC support Data Length Extension Feature, and very similar to KW40.