BT 5.0 on "ble_app_uart"

[Bar1]

Hi All,

I used the app "ble_app_uart"  and "ble_app_uart_c" on two custom boards mounting a n52840 QIAACO.

I know that in the app (nRF5_SDK_15.1.0_a8c0c4d\examples\ble_peripheral\ble_app_uart) is not used the BT 5.0 2phy but the 1phy.

My question is: what should I change to have a faster data transfer using the 2phy instead of 1phy from the peripheral to the central unit?

I tried just to replace BLE_GAP_PHY_1MBPS with BLE_GAP_PHY_2MBPS in the whole code but apparently it is not enough.

Thanks in advance,

[Stian Røed Hafskjold]

The peripheral/central needs to request a phy update and the central/peripheral needs to respond to it. Please check out the sequence diagrams:

http://infocenter.nordicsemi.com/topic/com.nordic.infocenter.s140.api.v6.1.0/group___b_l_e___g_a_p___c_e_n_t_r_a_l___p_h_y___u_p_d_a_t_e.html?cp=2_3_2_1_0_2_1_3_7_0

http://infocenter.nordicsemi.com/topic/com.nordic.infocenter.s140.api.v6.1.0/group___b_l_e___g_a_p___p_e_r_i_p_h_e_r_a_l___p_h_y___u_p_d_a_t_e.html?cp=2_3_2_1_0_2_1_3_7_1

Here the peripheral requests an update procedure. You can for example call this function in the ble_evt_handler under BLE_GAP_EVT_CONNECTED:

void phy_update_request(ble_evt_t const * p_ble_evt){
    ret_code_t err_code;
    ble_gap_phys_t const phys =
    {
        .rx_phys = BLE_GAP_PHY_2MBPS,
        .tx_phys = BLE_GAP_PHY_2MBPS,
    };
    err_code = sd_ble_gap_phy_update(p_ble_evt->evt.gap_evt.conn_handle, &phys);
    APP_ERROR_CHECK(err_code);
}

Central then responds in ble_evt_handler:

case BLE_GAP_EVT_PHY_UPDATE_REQUEST:
{
    NRF_LOG_DEBUG("PHY update request.");
    ble_gap_phys_t const phys =
    {
        .rx_phys = BLE_GAP_PHY_AUTO,
        .tx_phys = BLE_GAP_PHY_AUTO,
    };
    err_code = sd_ble_gap_phy_update(p_ble_evt->evt.gap_evt.conn_handle, &phys);
    APP_ERROR_CHECK(err_code);
} break;

[Bar1]

Hi Stian,

I did what you suggested but I did not get anything faster.

When I try to write something on the UART of ble_app_uart_peripheral, this message is sent to the ble_app_uart_c and also it is printed on the UART of ble_app_uart_peripheral which plays the role of echo.

Do you think that this can reduce the speed of the whole system? If yes what should I change in the code to do not have the "echo" on the ble_app_uart_peripheral.

Thanks in advance

[Stian Røed Hafskjold]

How do you define "faster data transfer"? And how do you measure it? The 1mbps and 2mbps PHY is only the on-air data transmission speed, and might not have any impact on application speed.

If you're talking about latency, then the connection interval is the parameter you need to have a look at. This is how often the packets are sent over air.

Then if you want to send a lot of data at a time, you can also look into the PDU MTU size (how many bytes per package), and connection event length (how many packets per connection interval).

Then finally you have the PHY (1mbps and 2mbps). If you increase to 2mbps, the radio time is shorter, meaning that you can fit more packets and more bytes per packet into one connection interval.