nRF52840 stops scanning

[Philip]

Hi.

We have a strange issue we are seeing with a nRF52840 where scanning fails, but it is very rare.

Setup - nRF52840 is a central device, and there are 20 x nRF52832's peripherals advertising. The central reports the status of all the peripherals to a PC via CDC usb.

The system can be running fine like this for 1 / 2 weeks 24 hours a day, then out of the blue the nRF52840 stops picking up any peripherals. It could be in the middle of the night, when the system isn't doing anything complicated like connecting / mass data transfer etc.

The fact that all the peripherals 'disappear' at the same time suggests the central is at fault. The peripherals have all been started at different times and have power etc.

I can't monitor / debug as it is a almost finished system, and the fault is too rare to wait and see it.

Are there any obvious properties I could monitor and report over so they are logged on the PC? All the BLE functions result in a hard restart if they fail which I am not seeing. This problem just occurs randomly, like the radio has just switched off etc.

Thanks

Phil

[bjorn-spockeli]

Hi Phillip, 

The system can be running fine like this for 1 / 2 weeks 24 hours a day, then out of the blue the nRF52840 stops picking up any peripherals. It could be in the middle of the night, when the system isn't doing anything complicated like connecting / mass data transfer etc.

The fact that all the peripherals 'disappear' at the same time suggests the central is at fault. The peripherals have all been started at different times and have power etc.

 It sounds like the nRF52840 stops scanning. Is the nRF52840 only scanning for the nRF52832 devices or or is it connected to all the nRF52832 devices? You could start a "watchdog" timer that is reset every time you receive an advertisment packet from one of the nRF52832 devices. If the timer times out, then you can call the SD-api to restart scanning. 

Do you log any debug information through the CDC USB interface?

Best regards

Bjørn

[Philip]

Hi Bjørn.

When it has had the problem it is only scanning, it is not connected to any of the nRF52832 devices.

What could cause the scanning to randomly stop?

I could add a watchdog timer, but would be better to figure out what the issue.

Is there any variables / functions I can monitor regarding scanning that I could log? e.g. is there a function that tells you if scanning is running, or has failed?

Thanks

Phil

[hmolesworth]

I find tracing all the scanning events helpful, something like this:

// Scan Events
static char * ble_scan_event_description[] =
{
/* NRF_BLE_SCAN_EVT_FILTER_MATCH",        */ " 0 Filter matched in the multifilter mode",
/* NRF_BLE_SCAN_EVT_WHITELIST_REQUEST:    */ " 1 Request the whitelist from the main application",
/* NRF_BLE_SCAN_EVT_WHITELIST_ADV_REPORT: */ " 2 Device from the whitelist is found",
/* NRF_BLE_SCAN_EVT_NOT_FOUND:            */ " 3 Filter not matched for the scan data",
/* NRF_BLE_SCAN_EVT_SCAN_TIMEOUT:         */ " 4 Scan timeout",
/* NRF_BLE_SCAN_EVT_SCAN_REQ_REPORT:      */ " 5 Scan request report",
/* NRF_BLE_SCAN_EVT_CONNECTING_ERROR:     */ " 6 Error occurred when establishing the connection from sd_ble_gap_connect",
/* NRF_BLE_SCAN_EVT_CONNECTED:            */ " 7 Connected to device"
};
#define NUM_BLE_SCAN_EVENTS (sizeof(ble_scan_event_description)/sizeof(ble_scan_event_description[0]))

/**@brief Function for handling Scanning Module events.
 */
static void scan_evt_handler(scan_evt_t const * p_scan_evt)
{
    ret_code_t err_code;

    switch(p_scan_evt->scan_evt_id)
    {
         case NRF_BLE_SCAN_EVT_CONNECTING_ERROR:     // Error occurred when establishing the connection. In this event, an error is passed from the function call @ref sd_ble_gap_connect
         {
              err_code = p_scan_evt->params.connecting_err.err_code;
              APP_ERROR_CHECK(err_code);
         } break;

         case NRF_BLE_SCAN_EVT_CONNECTED:            // Connected to device
         {
             ble_gap_evt_connected_t const * p_connected = p_scan_evt->params.connected.p_connected;
             // Scan is automatically stopped by the connection.
             NRF_LOG_INFO("Connect to Id %02x%02x%02x%02x%02x%02x",
                      p_connected->peer_addr.addr[0],
                      p_connected->peer_addr.addr[1],
                      p_connected->peer_addr.addr[2],
                      p_connected->peer_addr.addr[3],
                      p_connected->peer_addr.addr[4],
                      p_connected->peer_addr.addr[5]
                      );
         } break;

         case NRF_BLE_SCAN_EVT_SCAN_TIMEOUT:         // Scan timeout
         {
             NRF_LOG_INFO("Scan timed out.");
             scan_start();
         } break;

         case NRF_BLE_SCAN_EVT_FILTER_MATCH:         // A filter is matched or all filters are matched in the multifilter mode
             {
               ble_gap_evt_adv_report_t const *p_adv_report = p_scan_evt->params.filter_match.p_adv_report;
               NRF_LOG_INFO("Scan Match Id: %02x%02x%02x%02x%02x%02x",
                      p_adv_report->peer_addr.addr[0],
                      p_adv_report->peer_addr.addr[1],
                      p_adv_report->peer_addr.addr[2],
                      p_adv_report->peer_addr.addr[3],
                      p_adv_report->peer_addr.addr[4],
                      p_adv_report->peer_addr.addr[5]
                      );
             }
             break;

         case NRF_BLE_SCAN_EVT_NOT_FOUND:            // The filter was not matched for the scan data
             {
               ble_gap_evt_adv_report_t const *p_not_found = p_scan_evt->params.p_not_found;
               NRF_LOG_INFO("Deny Id: %02x%02x%02x%02x%02x%02x",
                      p_not_found->peer_addr.addr[0],
                      p_not_found->peer_addr.addr[1],
                      p_not_found->peer_addr.addr[2],
                      p_not_found->peer_addr.addr[3],
                      p_not_found->peer_addr.addr[4],
                      p_not_found->peer_addr.addr[5]
                      );
             }
             break;

         default:
//       case NRF_BLE_SCAN_EVT_FILTER_MATCH:         // A filter is matched or all filters are matched in the multifilter mode
         case NRF_BLE_SCAN_EVT_WHITELIST_REQUEST:    // Request the whitelist from the main application. For whitelist scanning to work, the whitelist must be set when this event occurs
         case NRF_BLE_SCAN_EVT_WHITELIST_ADV_REPORT: // Send notification to the main application when a device from the whitelist is found
//       case NRF_BLE_SCAN_EVT_NOT_FOUND:            // The filter was not matched for the scan data
         case NRF_BLE_SCAN_EVT_SCAN_REQ_REPORT:      // Scan request report
            if (p_scan_evt->scan_evt_id < NUM_BLE_SCAN_EVENTS)
            {
               NRF_LOG_INFO("scan_evt_id: %d %s", p_scan_evt->scan_evt_id, ble_scan_event_description[p_scan_evt->scan_evt_id]);
            }
            else
            {
               NRF_LOG_INFO("Unhandled scan_evt_id: %d", p_scan_evt->scan_evt_id);
            }
             break;
    }
}

Selectively enable/disable the event reports, but ensure everything generates a trace in case something wierd happes .. if any event happens that is ..

[Philip]

Hmm, thanks for the suggestion sounds good.

I will give it a try and monitor the events.

Thanks

Phil

[Philip]

Actually in the multi-link central SDK15.0.0 I am using there is no scan_init or scan_evt_handler? Must have been added in SDK15.2.0.

Phil