Change mac address before advertising (in on_ble_radio_active_evt call)

[rookie]

I am trying to change the mac address of my device every time I advertise a packet.  I have a callback on_ble_radio_active_evt where I update the address like this:

static void on_ble_radio_active_evt(bool radio_active)
{
    if (radio_active) {
        bd_addr.addr_type = BLE_GAP_ADDR_TYPE_RANDOM_STATIC;
        bd_addr.addr[0] = (uint8_t)NRF_FICR->DEVICEADDR[0];
        bd_addr.addr[1] = (uint8_t)(NRF_FICR->DEVICEADDR[0] >> 8);
        bd_addr.addr[2] = (uint8_t)(NRF_FICR->DEVICEADDR[0] >> 16) + count;
        bd_addr.addr[3] = (uint8_t)(NRF_FICR->DEVICEADDR[0] >> 24);
        bd_addr.addr[4] = (uint8_t)(NRF_FICR->DEVICEADDR[1]);
        bd_addr.addr[5] = (uint8_t)(NRF_FICR->DEVICEADDR[1] >> 8) | 0xc0;
        err_code = sd_ble_gap_addr_set(&bd_addr);
        
        // some custom data 
        append_advertisement_data(&advdata);
        
        err_code = ble_advdata_set(&advdata, NULL);
    }
}

but I get an error 8 ie NRF_ERROR_INVALID_STATE, which says Im not allowed to change the mac address in this state. How can I get around this error?

[Joakim Jakobsen]

Hi!

Do you know which funtion is returning the NRF_INVALID_STATE?
Is it the sd_ble_gap_addr_set(&bd_addr)?

If yes, I believe this root cause of this is the device is currently advertising, and you would need to stop the advertisement first.

sd_ble_gap_addr_set():

NRF_ERROR_INVALID_STATE - The identity address cannot be changed while advertising, scanning, or creating a connection.

Best regards,
Joakim

[rookie]

Hi Joakim,

Should I call sd_ble_gap_adv_stop() in the radio notification event, update my bd address and advertising packet and then start advertising with sd_ble_gap_adv_start? If I use the stop api, it throws off my advertisement interval. I am using a non connectable advertisement interval of 3 seconds, but if I stop the advertisement, I think it starts defaulting to the smallest interval possible. I was able to get around this by using a timer of 3 seconds and the following logic.

static void on_ble_radio_active_evt(bool radio_active)
    if (radio_active && adv_update) {
        adv_update = false;
        ret_code_t err_code;
        err_code = sd_ble_gap_adv_stop();
        APP_ERROR_CHECK(err_code);
        advertising_data_update(active);
        err_code = sd_ble_gap_adv_start(&m_adv_params, APP_BLE_CONN_CFG_TAG);
        APP_ERROR_CHECK(err_code);
    }
}

static void adv_timeout_handler(void * p_context)
{
    // every 3 seconds
    adv_update = true;

}

However I also have an initialization non connectable advert like this, whose timer value is actually not used:

static void non_connectable_adv_init(void)
{
    // Initialize advertising parameters (used when starting advertising).
    memset(&m_adv_params, 0, sizeof(m_adv_params));

    m_adv_params.type        = BLE_GAP_ADV_TYPE_ADV_NONCONN_IND;
    m_adv_params.p_peer_addr = NULL;                               // Undirected advertisement
    m_adv_params.fp          = BLE_GAP_ADV_FP_ANY;
    m_adv_params.interval    = NON_CONNECTABLE_ADV_INTERVAL; // also 3 seconds
    m_adv_params.timeout     = 0;
}

So this implementation seems unclean, though it works. Is there a better way to do this?

[Joakim Jakobsen]

That sounds strange.
The sd_ble_gap_adv_start() function should start the advertisement using the defined advertising parameters. I don't see how using the timer should change that. 

Which SDK/Softdevice are you using?