UART NUS Data length changed

[Dhillon]

In this function :

/**@brief Function for handling events from the GATT library. */
void gatt_evt_handler(nrf_ble_gatt_t * p_gatt, nrf_ble_gatt_evt_t const * p_evt)
{
if ((m_conn_handle == p_evt->conn_handle) && (p_evt->evt_id == NRF_BLE_GATT_EVT_ATT_MTU_UPDATED))
{
m_ble_nus_max_data_len = p_evt->params.att_mtu_effective - OPCODE_LENGTH - HANDLE_LENGTH;
NRF_LOG_INFO("Data len is set to 0x%X(%d)", m_ble_nus_max_data_len, m_ble_nus_max_data_len);
}
NRF_LOG_DEBUG("ATT MTU exchange completed. central 0x%x peripheral 0x%x",
p_gatt->att_mtu_desired_central,
p_gatt->att_mtu_desired_periph);
}

Getting Data Length changed (m_ble_nus_max_data_len) from 20 to 0xb6 (182).

I dont't know why ?? Where I can look for?

Thanks

[Dhillon]

Hi Hakon

Okay I want to keep data length 20 bytes.

What will be the value of NRF_SDH_BLE_GAP_DATA_LENGTH ??

And what is the calculation to know how much will be the data length depending upon NRF_SDH_BLE_GAP_DATA_LENGTH.

Thanks 

Bhupinderjeet Singh

[Hakon]

The lowest value possible for NRF_SDH_BLE_GAP_DATA_LENGTH is 27 so that's probably your best option.

[Dhillon]

Hi Hakon 

I changed to 27 but still the length is getting changed to 

<info> app: Data len is set to 0xB6(182)

I notice in sdk_config.h have this macro as well which might be playing role in the change of length:

NRF_SDH_BLE_GATT_MAX_MTU_SIZE

What would be possible value to have 20 Byte payload only.

Thanks

Bhupinderjeet Singh

[Hakon]

Ok, can you please send me all of your project files so that I can try to debug it?