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.

[LukeC]

nrf52-DK, SDK 12.2,softdevice 3.1

BLE uart com through the UART

Debug logging through the j-link RTT

RAM is changed in the linker

[Craig]

OK I have the same exact setup so that is good....what are you using to test it? Iphone? Android? What model? also I didn't do anything other than the code I sent you so I don't understand I can test tomorrow morning and verify my result....you shouldn't have any probles....did you run a terminal and get any debug messages about the agreed upon MTU size?

[FormerMember]

In SDK 13.0.0 there is a GATT module that handles data length update related events, see gatt_init() --> nrf_ble_gatt_init(). Perhaps it could be useful to take a look at it?

[LukeC]

After doing some sleuthing on the crash data, it seems my error is in the softdevice_handler.c,

err_code = sd_ble_evt_get(mp_ble_evt_buffer, &evt_len);

This function fails with a NRF_ERROR_DATA_SIZE

My thought to fix this was to set the NRF_BLE_GATT_MAX_MTU_SIZE to allow for larger GATT chars.

This seems to work with single long writes, but when I push a lot of data (1kb file) the nRF52 gets hung on FIFO handling. Perhaps my UART is not able to push the data out fast enough? At 115kbps for the uart you would think that would not pose any issues.

[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.