how to initialize event handler??

Question

Hi all,
i am doing a BLE project using nrf51822 hardware,
in this project my requirement is to initialize the event,
for doing that i took ble_app_proximity,ble_app_hrs as reference code , 
 so what i did to meet my requirement is ,
 from main() i called services_init()
 and in this i intialize 
 ble_hrs_init_t->evt_handler=evt_handler;[refered from ble_app_hrs ]
 and my evt_handlert defination is like this 
 evt_handler(ble_hrs_t *p_nus, ble_hrs_evt_t * p_evt)
 it seems there is two type of structure related to evnt
 1)typedef struct
	{
 ble_hrs_evt_type_t evt_type; /**< Type of event. */
	} ble_hrs_evt_t;
 2)typedef struct
	{
 ble_evt_hdr_t header; /**< Event header. */
 union
 {
 ble_common_evt_t common_evt; /**< Common Event, evt_id in BLE_EVT_* series. */
 ble_gap_evt_t gap_evt; /**< GAP originated event, evt_id in BLE_GAP_EVT_* series. */
 ble_l2cap_evt_t l2cap_evt; /**< L2CAP originated event, evt_id in BLE_L2CAP_EVT* series. */
 ble_gattc_evt_t gattc_evt; /**< GATT client originated event, evt_id in BLE_GATTC_EVT* series. */
 ble_gatts_evt_t gatts_evt; /**< GATT server originated event, evt_id in BLE_GATTS_EVT* series. */
 } evt;
	} ble_evt_t;
 so my doubt is:
 1) which data structure should use as second pararameter of evt_handler either ble_hrs_evt_t or ble_evt_t?
 2)if i use ble_hrs_evt_t as second parameter, then this has member ble_hrs_evt_type_t which is enum of this type
 typedef enum
 {
 BLE_HRS_EVT_NOTIFICATION_ENABLED, /**< Heart Rate value notification enabled event. */
 BLE_HRS_EVT_NOTIFICATION_DISABLED /**< Heart Rate value notification disabled event. */
 } ble_hrs_evt_type_t;
 so in this can i define my own event type?
 3) under what situations is one data structure preferred over other, for example in ble_hrs ble_hrs_evt_t; is used 
 4) under ble_app_proximity project, the ble_evt_t is used and i wanted to know the reason behind using this structure as compared to 
 point 3.
 
 Can any one please share information related to this....?
Thanks
Renu

FormerMember · Accepted Answer

The second parameter of the event handler should be ble_evt_t . When receiving a BLE event, it is in the format of ble_evt_t . 
 When receiving an event, ble_evt_t should used, see 1. As you can see in ble_hrs.c, ble_hrs_evt_t is used to "process" a received event in on_hrm_cccd_write(..) . on_hrm_cccd_write is called in on_write , and on_write(..) receives the BLE event in the format of ble_evt_t . 
 
 Edit: 
 ble_app_proximity: the purpose of the event handler on_ias_evt is to handle immediate alert service events. BLE_IAS_EVT_ALERT_LEVEL_UPDATED-is passed to the application from
 ble_evt_dispatch(..) --> ble_ias_on_ble_evt(..) --> on_write(..) --> p_ias->evt_handler(..) : 
 static void on_write(ble_ias_t * p_ias, ble_evt_t * p_ble_evt)
{
 ble_gatts_evt_write_t * p_evt_write = &p_ble_evt->evt.gatts_evt.params.write;

 if ((p_evt_write->handle == p_ias->alert_level_handles.value_handle) && (p_evt_write->len == 1))
 {
 // Alert level written, call application event handler
 ble_ias_evt_t evt;

 evt.evt_type = BLE_IAS_EVT_ALERT_LEVEL_UPDATED;
 evt.params.alert_level = p_evt_write->data[0];

 p_ias->evt_handler(p_ias, &evt);
 }
} 
 
 ble_app_hrs is built the same way: ble_evt_dispatch(..) --> ble_hrs_on_ble_evt(..) --> on_write(..) --> on_hrm_cccd_write(..) . However, there are no events associated with notifications enabled or disabled. And therefore, it is no need for an event handler, so the event handler that is called is null: 
 static void on_hrm_cccd_write(ble_hrs_t * p_hrs, ble_gatts_evt_write_t * p_evt_write)
{
 if (p_evt_write->len == 2)
 {
 // CCCD written, update notification state
 if (p_hrs->evt_handler != NULL)
 {
 ble_hrs_evt_t evt;

 if (ble_srv_is_notification_enabled(p_evt_write->data))
 {
 evt.evt_type = BLE_HRS_EVT_NOTIFICATION_ENABLED;
 }
 else
 {
 evt.evt_type = BLE_HRS_EVT_NOTIFICATION_DISABLED;
 }

 p_hrs->evt_handler(p_hrs, &evt);
 }
 }
}
 
 The purpose of softdevice_sys_evt_handler_set(..) is to register system events from the softDevice, see its documentation here . 
 The purpose of softdevice_ble_evt_handler_set(..) is to register a handler for BLE events, see its documentation here .