sd_app_evt_wait() for power management

[thoric_fish]

Hi my goal is to put the NRF into system on low power mode every other second. I have a repeated app_timer that increments counter variable m_custom_value every second. I thought of two possible ways to do this by calling sd_app_evt_wait() if/while m_custom_value % 2 == 0. 

1. I was wondering if there is any difference if I use an if statement vs while loop to call sd_app_evt_wait(). If I use an if statement then sd_app_evt_wait() is only called once every other second, but if I use a while loop then sd_app_evt_wait() is called continuously for the duration of one second (or approximately one second), every other second. Will using a while loop just interrupt the NRF CPU from sleep or is there no difference between calling sd_app_evt_wait() once or calling sd_app_evt_wait() continuously for the duration where I want the NRF CPU to be sleeping? 

2. Do I need to make sure the NRF is done advertising or force the NRF to stop advertising before calling sd_app_evt_wait() if I want the NRF CPU to go to system on low power mode?

I noticed that if I start BLE advertising then call sd_app_evt_wait() the NRF DK will continue advertising until the advertising timeout or idle power-management code is called. So my current assumption is that if BLE advertising is still active when sd_app_evt_wait() is called, then the NRF CPU will not go to sleep and the active BLE advertising will continue draining significant power. 

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#define NOTIFICATION_INTERVAL APP_TIMER_TICKS(1000)

APP_TIMER_DEF(m_busy_wait_timer_id);

static uint8_t m_custom_value = 0;

static void notification_timeout_handler(void * p_context)

{

UNUSED_PARAMETER(p_context);

ret_code_t err_code;

// Increment the value of m_custom_value before notifying it.

m_custom_value++;

}

static void timers_init(void)

{

// Initialize timer module.

ret_code_t err_code = app_timer_init();

APP_ERROR_CHECK(err_code);

app_timer_create(&m_notification_timer_id, APP_TIMER_MODE_REPEATED, notification_timeout_handler);

}

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#define NOTIFICATION_INTERVAL           APP_TIMER_TICKS(1000)    
APP_TIMER_DEF(m_busy_wait_timer_id);
static uint8_t m_custom_value = 0;

static void notification_timeout_handler(void * p_context)
{
    UNUSED_PARAMETER(p_context);
    ret_code_t err_code;
    
    // Increment the value of m_custom_value before notifying it.
    m_custom_value++;
}

static void timers_init(void)
{
    // Initialize timer module.
    ret_code_t err_code = app_timer_init();
    APP_ERROR_CHECK(err_code);

    app_timer_create(&m_notification_timer_id, APP_TIMER_MODE_REPEATED, notification_timeout_handler);
}

static void application_timers_start(void)
{
       app_timer_start(m_notification_timer_id, NOTIFICATION_INTERVAL, NULL);

}
    

int main(void)
{
    bool erase_bonds;

    // Initialize.
    log_init();
    timers_init();
    application_timers_start();
    buttons_leds_init(&erase_bonds);
    power_management_init();
    ble_stack_init();
    gap_params_init();
    gatt_init();
    peer_manager_init();
    
    services_init();
    advertising_init();
    conn_params_init();
  
    NRF_LOG_INFO("Template example started.");
    advertising_start(erase_bonds);
    
    // Enter main loop.
  for (;;)
    {
        while(m_custom_value % 2 == 0){
            sd_app_evt_wait();
        }
        // vs? 
        if(m_custom_value % 2 == 0){
            sd_app_evt_wait();
        }
    } 
    
}