I need help increasing ATT MTU.

[julian24]

Hello everyone,

I'm pretty new with BLE configurations. I'm currently implementing a BLE NUS service, and noticed that on the example code the max length supported is 20. I've read some documentation saying that this max length can be increased, but I don't exactly know how to do it.

I was wondering if there is some documentation or tutorial regarding this topic, since I'd like to know not only how to increase the max length supported over BLE NUS but also the implicancies of doing it.

I'm using nRF52 DK with SDK v17.1 and softdevice S132, with Segger Embedded Studio on Windows 10.

Thanks for reading.

[Hieu]

Hi julian24,

You will need to change NRF_SDH_BLE_GATT_MAX_MTU_SIZE in sdk_config.h. That being said, I believe it is already setup to a big value in the NUS example.

If you are just beginning to explore using nRF device for BLE, I recommend using the nRF Connect SDK though. The nRF5 SDK is in maintenance mode and will not receive any feature updates.

Hieu

[julian24]

Hi Hieu,

in the NUS example, NRF_SDH_BLE_GATT_MAX_MTU_SIZE  is set to 23, which means the max length supported over NUS is 20, and it's just not enough for my program.

Can I just set NRF_SDH_BLE_GATT_MAX_MTU_SIZE to, say, 103, so i can work with a max length of 100? Are there no consequences or anything to consider regarding this? I remember that on nRF51822 23 was the max possible value.

Thanks for your help

[Hieu]

Hi julian24,

23 probably was the max possible value in the very first release of Bluetooth LE. With the SDK you are using, 103 is perfectly possible.

Once again, please use the nRF Connect SDK if possible.

[julian24]

Okay, so this was much simpler than i thought. Thanks for clarifying, I'll consider connect SDK