Why TXPOWER register is toggling?

[deepu301]

Hello

I want to modify the tx powel level to 4 dbm using sd_ble_gap_tx_power_set(BLE_GAP_TX_POWER_ROLE_ADV, m_adv_handle, 4); after Advertising_Init function.

void Advertising_Init_V(void)
{
...
...
...
    APP_ERROR_CHECK(err_code);
 
    err_code = ble_advdata_encode(&srdata, m_adv_data.scan_rsp_data.p_data, &m_adv_data.scan_rsp_data.len);
    APP_ERROR_CHECK(err_code);
 
    // Set advertising parameters.
    memset(&m_adv_params, 0, sizeof(m_adv_params));
 
    m_adv_params.primary_phy     = BLE_GAP_PHY_1MBPS;
    m_adv_params.duration        = APP_ADV_DURATION;
    m_adv_params.properties.type = BLE_GAP_ADV_TYPE_CONNECTABLE_SCANNABLE_UNDIRECTED;
    m_adv_params.p_peer_addr     = NULL;
    m_adv_params.filter_policy   = BLE_GAP_ADV_FP_ANY;
    m_adv_params.interval        = APP_ADV_INTERVAL;
 
    err_code = sd_ble_gap_adv_set_configure(&m_adv_handle, &m_adv_data, &m_adv_params);
    APP_ERROR_CHECK(err_code);

    err_code = sd_ble_gap_tx_power_set(BLE_GAP_TX_POWER_ROLE_ADV, m_adv_handle, tx_power_level);
    APP_ERROR_CHECK(err_code);
}

I could able run the code with out issue, when verifying TXPOWER register i observed the value in register is toggling between 0 and 4 as attached video . Even i tried directly update register but its going hard fault after digging through documentation i found RADIO registers are blocked for access. What I want understand is toggling of value is expected behavior or its an issue.

[awneil]

Halting execution while the SoftDevice is running will cause a Hard Fault:

https://devzone.nordicsemi.com/f/nordic-q-a/51719/nrf52840-dongle-debugging/207731#207731

[deepu301]

Thank you awneil.

awneil said:

Halting execution while the SoftDevice is running will cause a Hard Fault:

I am aware of that behavior but the value toggling of TXPOWER register is observed  when softdevice is running without any breakpoints. we observed this behavior during run-time viewing of Register value.

[awneil]

Why are you looking at that register?

As you've already said, it is managed by the SoftDevice - so it's not a concern of your app.

[Sigurd]

deepu301 said:

What I want understand is toggling of value is expected behavior or its an issue.

The toggling is expected. It's only set to tx_power_level when the RADIO is sending advertising packets, and defaults back to 0 afterwards when RADIO is not active. As awneil says, this is managed by the SoftDevice.

[deepu301]

Okay.. Thank you.