where use sd_ble_gattc_read

Question

Hi,
I would like read a long characteristic.
I know that I have to use sd_ble_gattc_read and I have to multiple call this function.
But I don't know where I have to call this function?
After service discovery in this block? In some 'for loop' ? 
 if (p_evt->evt_type == BLE_DB_DISCOVERY_COMPLETE &&
 p_evt->params.discovered_db.srv_uuid.uuid == BLE_DEUFOL_SERVICE_UUID &&
 p_evt->params.discovered_db.srv_uuid.type == p_deufol->uuid_type)
 {
counter++;
for(uint16_t x=0;x<25;x++)
 err_code = sd_ble_gattc_read(p_deufol->conn_handle,p_chars[i].characteristic.handle_value , x * 20);


}
 
 You don't have any central example for long read. 
 When I tried use volatile global variable as counter, but counter is still zero. I increased counter in that block too. Why this variable is not hold in memory ?

gorazd · Accepted Answer

Hi, 
 dont call functions which trigger events inside event handlers. 
 Call sd_ble_gattc_read inside main anytime you have a connection (m_conn_handle != BLE_CONN_HANDLE_INVALID). 
 After you get BLE_GATTC_EVT_READ_RSP, call sd_ble_gattc_read(m_conn_handle, handle, 20) again with some offset (e.g. 20). 
 Again, wait for the BLE_GATTC_EVT_READ_RSP, and then you can concatenate the first and the second data into one (array) variable.