[BLE] why restart advertising after disconnect?

Question

Hi, 
 My project is combined 'Multi-link Central Example' and 'ble_app_uart', so that it is a central that can be connected to multiple peripherals and a peripheral that can be connected to a single central. 
 When I disconnect from the central which is mobile phone, it immediately restarts advertising. 
 (This is BLE_GAP_EVT_DISCONNECTED case in ble_advertising_on_ble_evt function.) 
 static void on_disconnected(ble_advertising_t * const p_advertising, ble_evt_t const * p_ble_evt)
{
 uint32_t ret;

 p_advertising->whitelist_temporarily_disabled = false;


 if (p_ble_evt->evt.gap_evt.conn_handle == p_advertising->current_slave_link_conn_handle &&
 p_advertising->adv_modes_config.ble_adv_on_disconnect_disabled == false)
 {
 ret = ble_advertising_start(p_advertising, BLE_ADV_MODE_DIRECTED_HIGH_DUTY);
 if ((ret != NRF_SUCCESS) && (p_advertising->error_handler != NULL))
 {
 p_advertising->error_handler(ret);
 }
 }
} 
 1. my question is, what is meaning of 
 " if (p_ble_evt->evt.gap_evt.conn_handle == p_advertising->current_slave_link_conn_handle && p_advertising->adv_modes_config.ble_adv_on_disconnect_disabled == false) " 
 and why it restart advertising? 
 
 And, when it restarts advertising because of above code part, BLE_GAP_EVT_DISCONNECTED case in the ble_evt_handler is not triggered. 
 (but it triggered well if I erase restart advertising code part..) 
 2. Does this mean that it didn't disconnected properly? Why this problem happening? 
 
 BR, 
 lyrics

Einar Thorsrud · Accepted Answer

Hi Lyrics,

1. my question is, what is meaning of

" if (p_ble_evt->evt.gap_evt.conn_handle == p_advertising->current_slave_link_conn_handle &&
p_advertising->adv_modes_config.ble_adv_on_disconnect_disabled == false) "

and why it restart advertising?

The reason the advertising module supports automatically starting to advertise upon a disconnect is that this is a very common scenario. However this is configurable and if you do not want it, you can disable it. Looking at the code snippet you posed, you see the ble_adv_on_disconnect_disabled field is what is relevant here. This can be set in the configuration struct before you call ble_advertising_init(), as is demonstrated in <SDK 17.0.2>\examples\ble_peripheral\experimental\ble_app_cgms\main.c. You can also set it at a later point if you want it normally on, but to disable it at a specific point, as demonstrated in for instance <SDK17.0.2>\examples\ble_peripheral\ble_app_buttonless_dfu\main.c.

And, when it restarts advertising because of above code part, BLE_GAP_EVT_DISCONNECTED case in the ble_evt_handler is not triggered.

(but it triggered well if I erase restart advertising code part..)

2. Does this mean that it didn't disconnected properly? Why this problem happening?

I did not get that. You should always get the BLE_GAP_EVT_DISCONNECTED if there as been a disconnect. Can you explain in more detail? Where do you look for the event, and in what situation? Please elaborate.

[BLE] why restart advertising after disconnect?

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