Problem ATTERR_APP_BEGIN in NRF Connect app

[CME]

Hello,

I would like to know wich step I forget to do to send more than 20 bytes in NRF Connect app to a BL652. I followed some talks and subjects about it but it's doesn't work

I changed the NRF_SDH_BLE_GATT_MAX_MTU_SIZE by 64 in the sdk_config.h.

I saw in "BL652 Data Length Extension.pdf", if I changed this parameter I must changed the NRF_SDH_BLE_GAP_DATA_LENGTH parameter (NRF_SDH_BLE_GATT_MAX_MTU_SIZE +  4)

That's true?

Next, I increased NRF_SDH_BLE_GAP_EVENT_LENGTH to 10.

I modified accordingly the RAM START and SIZE in option.

After this modifications, I don't understand why my characteristic doesn't work with more 20 bytes.

Thanks for your help.

CME

[Simonr]

Hi

The MTU size is changed based on a negotiation between master and slave devices in an ATT exchange MTU request/response, where the lowest value in the negotiation is chosen. Your BL652 module supports larger MTU sizes, but the SoftDevices for nRF51 series devices (S110, S120, S130) only support an MTU_SIZE of 23, which limits the user data to 20 bytes because of the 3 byte overload required.

Best regards,

Simon