Best way to detect when a client subscribes to the NUS

Question

Hi, 
 So we have a project where we use the NUS, and we need to detect when a client subscribes. We eventually found a way, but it seems very obtuse and a bit black magic, so we wondered if this was the way things are "supposed" to work. Can you confirm? 
 First we register a handler on BLE events when we initialise the SD: 
 
 NRF_SDH_BLE_OBSERVER(m_ble_observer, APP_BLE_OBSERVER_PRIO, ble_evt_handler, NULL); 
 
 Then in our handler we do this (actually a lot more but shortened for this post):

static void ble_evt_handler(ble_evt_t const * p_ble_evt, void * p_context) 
 { 
 if ( p_ble_evt->header.evt_id == BLE_GATTS_EVT_WRITE && p_ble_evt->evt.gatts_evt.params.write.data[0] == 1 ) 
 { 
 // do on subscribe stuff here 
 } 
 } 
 
 (But surely there must be an easier way?) 
 
 thanks

user4240 · Accepted Answer

Hi, 
 The NUS service will actually raise an event when notifications are enabled/disabled by the client, but the ble_app_uart example does not subscribe for these events by default so it might be easy to overlook. You can "subscribe" for these events in the nus_data_handler(): 
 /**@brief Function for handling the data from the Nordic UART Service.
 *
 * @details This function will process the data received from the Nordic UART BLE Service and send
 * it to the UART module.
 *
 * @param[in] p_evt Nordic UART Service event.
 */
/**@snippet [Handling the data received over BLE] */
static void nus_data_handler(ble_nus_evt_t * p_evt)
{

 
 switch (p_evt->type) 
 {
 case BLE_NUS_EVT_RX_DATA:
 {
 
 uint32_t err_code;

 NRF_LOG_DEBUG("Received data from BLE NUS. Writing data on UART.");
 NRF_LOG_HEXDUMP_DEBUG(p_evt->params.rx_data.p_data, p_evt->params.rx_data.length);

 for (uint32_t i = 0; i < p_evt->params.rx_data.length; i++)
 {
 do
 {
 err_code = app_uart_put(p_evt->params.rx_data.p_data[i]);
 if ((err_code != NRF_SUCCESS) && (err_code != NRF_ERROR_BUSY))
 {
 NRF_LOG_ERROR("Failed receiving NUS message. Error 0x%x. ", err_code);
 APP_ERROR_CHECK(err_code);
 }
 } while (err_code == NRF_ERROR_BUSY);
 }
 if (p_evt->params.rx_data.p_data[p_evt->params.rx_data.length - 1] == '')
 {
 while (app_uart_put('
') == NRF_ERROR_BUSY);
 }
 } break;

 case BLE_NUS_EVT_COMM_STARTED:
 NRF_LOG_INFO("Notifications enabled");
 break;
 
 case BLE_NUS_EVT_COMM_STOPPED:
 NRF_LOG_INFO("Notifications disabled");
 break;

 default:
 break;
 }

} 
 Best regards, 
 Vidar

Best way to detect when a client subscribes to the NUS

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