Large MTU + DLE Softdevice Crash

[LukeC]

Hello,

I have followed a couple of the posts on the devzone on how to increase the MTU and add the DLE support such as this.

However, whenever I send over 20 bytes of data I get an "app_error_fault".

• I have logging enabled and changed my ram size so my ram should be set correctly.

• I have set the MTU size in sdk_config.h:

  #define NRF_BLE_MAX_MTU_SIZE 75

• I set the att size in the setup function

  ble_enable_params.gatt_enable_params.att_mtu = NRF_BLE_MAX_MTU_SIZE;

• I have set the DLE options

  ble_opt_t opt; memset(&opt, 0, sizeof(opt));

    opt.common_opt.conn_evt_ext.enable = 1;  //DLE
    
    err_code = sd_ble_opt_set(BLE_COMMON_OPT_CONN_EVT_EXT, &opt);
    APP_ERROR_CHECK(err_code);
    
    opt.gap_opt.ext_len.rxtx_max_pdu_payload_size = NRF_BLE_MAX_MTU_SIZE+4; //DLE
    
    err_code = sd_ble_opt_set(BLE_GAP_OPT_EXT_LEN, &opt);
    APP_ERROR_CHECK(err_code);
  

5. I changed ble_nus.h to use the longer MTU size:

   *//#define BLE_NUS_MAX_DATA_LEN (GATT_MTU_SIZE_DEFAULT - 3) /< Maximum length of data (in bytes) that can be transmitted to the peer by the Nordic UART service module. */ #define BLE_NUS_MAX_DATA_LEN (NRF_BLE_MAX_MTU_SIZE - 3) /< Maximum length of data (in bytes) that can be transmitted to the peer by the Nordic UART service module. /

Any ideas as to why the softdevice would crash on a long write? I get a message saying I have requested the longer MTU by the central as well.

[Craig]

I just did this yesterday, can you post your files here? You need to request the MTU from the central upon connection established. You can use a function sd_ble_request_mtu() I believe that is what its called....I can lookup my notes

[FormerMember]

To check if UART is the problem, you can temporarily disable the UART functionality or for example transmit only one of the transmitted bytes per packet over UART.

The example ble_central_and_peripheral/experimental/ble_att_mtu_throughput shows how to test long MTU, but it doesn't transfer the received data over UART.