How to change the default MTU size of the BLE central (ble_app_blinky_c)?

[Dhyanes]

I am using ble_app_blinky_c application for my project. I want to update my central's default MTU size from 23 to 150 and I know my peripheral device supports MTU size of 150 bytes (tested it using NRF connect phone application).  In order to do that, I tried changing the macro "NRF_SDH_BLE_GATT_MAX_MTU_SIZE" from 23 to 150 and by doing so my application goes in to system reset loop and the error i get the "NRF_ERROR_NO_MEM" error. Please help me with this issue or suggest some other ways to update the central's MTU size. Advance thank you for the answers.

[Turbo J]

Expected behaviour: You have to change the linker settings in order to fullfill the softdevices larger RAM requirements. Check your linker script, and also check the log messages - it should tell you how what RAM setting would be required.

[Dhyanes]

Hi Turbo,

I could update the RAM settings, thank you for the answer. But still the central is not able to send more than 20 bytes while writing for a characteristic and I get an invalid data size error as a return statement. Do you have an idea on how to solve this issue? Advance thank you.

[Amanda Hsieh]

Hi Dhyanes,

Dhyanes said:

I get an invalid data size error as a return statement.

Did you increase the characteristic length (.max_len)?

Please see Step 2.H, Set characteristic length in the Bluetooth low energy Characteristics, a beginner's tutorial.  

The latest question seems it's not related to the subject.  

If you have any new questions, please create a new support case. It will be easy for other users to search on the Devzon.   

[Dhyanes]

Hi Amanda,

Thank you for the answers. I am trying to send around 30 bytes from central to a peripheral (non-nrf device).  And the invalid data size error comes on the server-side. I am able to send more than 120 bytes to the same peripheral using NRF connect phone application, but I am not able to send them using ble_central_app_blinky application. And I assume the solution you had provided, needs to be worked in client-side, but in this case, I am using different ble peripheral. Please help me with the same.

regards

Dhyanes

[Amanda Hsieh]

Hi, 

Only the client side can write data to the server. Please see the following figure:

-Amanda H.

[Dhyanes]

Hi,

Thank you for the answers. I want to know how a BLE central can write more than 20 bytes to the BLE peripheral's characteristics. So in reference to your answer, I am not bit clear for data transfers.

regards

Dhyanes

[Amanda Hsieh]

Hi, 

You can refer to Vidar Berg's suggestion in this post. 

This post also might help.  

-Amanda H