ble gap data length update function return resources error

[Umer Mahmood]

problem: in BLE data length negotiation , In the response from slave tx  doesnt go above 216, and rx doesnot go above 54. 

s140

Experimental UDP example - sdk v16.0 (UDP example)

Gatt module added and initialized 

MIN_CONN_INTERVAL 6   // increasing or decreasing this doesnt have any effect

MIN_CONN_INTERVAL  6 /// increasing or decreasing this doesnt have any effect

static void gap_params_set(void)
{
    memset(&m_gap_params, 0x00, sizeof(m_gap_params));

    BLE_GAP_CONN_SEC_MODE_SET_OPEN(&m_gap_params.sec_mode);

    m_gap_params.appearance = BLE_APPEARANCE_UNKNOWN;

    m_gap_params.p_dev_name   = (const uint8_t *)DEVICE_NAME;
    m_gap_params.dev_name_len = strlen(DEVICE_NAME);

    m_gap_params.gap_conn_params.min_conn_interval = (uint16_t)MIN_CONN_INTERVAL;
    m_gap_params.gap_conn_params.max_conn_interval = (uint16_t)MAX_CONN_INTERVAL;
    m_gap_params.gap_conn_params.slave_latency     = SLAVE_LATENCY;
    m_gap_params.gap_conn_params.conn_sup_timeout  = CONN_SUP_TIMEOUT;
}

in sdk_config:

NRF_SDH_BLE_GAP_DATA_LENGTH 251
NRF_SDH_BLE_GAP_EVENT_LENGTH 320
NRF_SDH_BLE_GATT_MAX_MTU_SIZE 247

        case BLE_GAP_EVT_DATA_LENGTH_UPDATE_REQUEST:
        {
            NRF_LOG_DEBUG("BLE_GAP_EVT_DATA_LENGTH_UPDATE_REQUEST");
            ble_gap_data_length_params_t response = {
            .max_tx_octets =100,
            .max_rx_octets = 100,
            .max_tx_time_us = BLE_GAP_DATA_LENGTH_AUTO,
            .max_rx_time_us = BLE_GAP_DATA_LENGTH_AUTO
};
            ble_gap_data_length_limitation_t lims;
            ret_code_t err_code;
            err_code = sd_ble_gap_data_length_update(p_ble_evt->evt.gap_evt.conn_handle, &response, &lims);
            .....
            .....

returned error code is : NRF_ERROR_RESOURCES

ble_gap_data_length_limitation_t shows:

tx limit 0

rx limit 46

tx_rx_time_limit 0x00

If I try this:

err_code = sd_ble_gap_data_length_update(p_ble_evt->evt.gap_evt.conn_handle, &response, &lims);

and observe OTA using sniffer I see: from master

and response from slave as:

[Vidar Berg]

Hello,

This example does not call nrf_sdh_ble_default_cfg_set() to apply the SDK config settings when enabling the Softdevice in ble_stack_init() like the regular SDK examples, so the Softdevice does not get configure to support NRF_SDH_BLE_GATT_MAX_MTU_SIZE=247.  I think this must be the reason you get NRF_ERROR_RESOURCES.

[Umer Mahmood]

indeed, it does not. 

I am going to try this

    // Configure the BLE stack using the default settings.
    // Fetch the start address of the application RAM.
    uint32_t ram_start = 0;
    err_code = nrf_sdh_ble_default_cfg_set(APP_BLE_CONN_CFG_TAG, &ram_start);
    APP_ERROR_CHECK(err_code);

and get back to you. 

But is there any possibility that, it is impossible for softdevice to handle MAX data length configuration since being used in ipv6 over ble example?  I mean due to any memory/ram limitations or something? 

[Umer Mahmood]

Still getting the same resources error!

[Vidar Berg]

Sorry, I haven't worked that much with L2CAP CoC, but I asked our stack team about this and they noted that the Data length cannot exceed the buffer limits BLE_IPSP_RX_MPS and BLE_IPSP_TX_MPS. So it should work if you set  BLE_IPSP_RX_MPS to 100 and increase the app_ram_base accordingly (see debug log for new RAM settings).

[Umer Mahmood]

Thank you so much. It works perfectly, I am able to now set rx and tx data length to max i.e 251 bytes.