Increase hvn_tx_queue_size to maximize throughput

[Alexander]

I posted on the forum regarding the same project here https://devzone.nordicsemi.com/f/nordic-q-a/34022/optimizing-throughput-with-multiple-central-links-and-1-peripheral-link.

I wan't to stream with about 25kb/s as a minimum. Iv'e calcuated that if using 100ms conn interval I would need to set NRF_SDH_BLE_GAP_EVENT_LENGTH = 25ms. This would give me approximately 52 packets of 100bytes guaranteed per conn interval. I'm streaming data using notifications as a peripheral to a central device. I'm thinking that I would like to increase the TX buffer (hvn_tx_queue_size ) to increase the throughput. But if I increase it to above 11 i get NRF_ERROR_NO_MEM when running nrf_sdh_ble_enable(). This is fine, I check what RAM settings I should use and try, but I still get same error.

I also initiate with 19 central links so I eat alot of RAM. If I change to 1 central link I can go up to hvn_tx_queue_size = 17.

Is there a max value for hvn_tx_queue_size? Or is there a max value for softDevice RAM allocation? Does it matter what hvn_tx_queue_size is set to if I push data really fast? Do I need a big TX buffer to be able to send as many as 52 packets in 1 connection interval?

That was alot of questions, but I feel a bit confused to why I can't enable the sd with these settings.

Here is the code in ble_stack_init()

static void ble_stack_init(void)
{
    ret_code_t err_code;

    err_code = nrf_sdh_enable_request();
    APP_ERROR_CHECK(err_code);

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

    ble_cfg_t ble_cfg;
    memset(&ble_cfg, 0, sizeof ble_cfg);
    ble_cfg.conn_cfg.conn_cfg_tag = APP_BLE_CONN_CFG_TAG;
    ble_cfg.conn_cfg.params.gatts_conn_cfg.hvn_tx_queue_size = 17;
    err_code = sd_ble_cfg_set(BLE_CONN_CFG_GATTS, &ble_cfg, ram_start);
    APP_ERROR_CHECK(err_code);

    // Enable BLE stack.
    err_code = nrf_sdh_ble_enable(&ram_start);
    APP_ERROR_CHECK(err_code);

    // Register a handler for BLE events.
    NRF_SDH_BLE_OBSERVER(m_ble_observer, APP_BLE_OBSERVER_PRIO, ble_evt_handler, NULL);
}

[Alexander]

Ok, so I ran into a similar problem again. I want to set NRF_SDH_BLE_GATT_MAX_MTU_SIZE to 247. It is currently set to 100. When I set it to 247 i get this error ouput on RTT 

<warning> nrf_sdh_ble: Insufficient RAM allocated for the SoftDevice.
<warning> nrf_sdh_ble: Change the RAM start location from 0x20010DF8 to 0x2001EE58.
<warning> nrf_sdh_ble: Maximum RAM size for application is 0x211A8.
<error> nrf_sdh_ble: sd_ble_enable() returned NRF_ERROR_NO_MEM.
<error> app: ERROR 4 [NRF_ERROR_NO_MEM] at ../src/ble_core.c:435
PC at: 0x00026E85
<error> app: End of error report

I then change to those settings in my linker script and build and flash. I then get this error output

error> nrf_sdh_ble: sd_ble_enable() returned NRF_ERROR_NO_MEM.
<error> app: ERROR 4 [NRF_ERROR_NO_MEM] at ../src/ble_core.c:435
PC at: 0x00026E85
<error> app: End of error report

Basically the same as before but no suggestion to change RAM settings. How can this be?