Simple Observing of nearby devices

[Gordon]

Hi, I have an nRF51822 with s130 doing normal advertising and a Nordic UART service. Is there an example somewhere of doing some simple observation with it at the same time?

Ideally I'd just have start_listening and end_listeningfunctions, and would then get the event handler called whenever an advertising packet was received (which would contain signal strength info?). No connection needed at all.

Would the softdevice need configuring in central mode for this? I'm short on RAM so the less the Soft Device takes the better.

thanks!

[Einar Thorsrud]

There is just one concurrent BLE Central & Peripheral example in SDK 11, the experimental BLE Relay Example. It is probably a bit more complex than what you need, but it demonstrates how the device can act as a peripheral (both advertising and keeping connections) and as a central (including scanning).

[Gordon]

Thanks - so sd_ble_gap_scan_start is the magic function that's needed by the look of it, and you get a BLE_GAP_EVT_ADV_REPORT in on_ble_central_evt? Does the softdevice have to have CENTRAL_LINK_COUNT>0? Ideally not since there would be no link as such?

[Einar Thorsrud]

Yes, that is correct. As long as you only scan for peripherals and never initiate a connection, you can set CENTRAL_LINK_COUNT to 0 in order to reduce the amount of RAM required by the SoftDevice.

[Gordon]

Ok, in case anyone else is interested in this - with Einar's help:

#define SCAN_INTERVAL              0x00A0                             /**< Determines scan interval in units of 0.625 millisecond. */
#define SCAN_WINDOW                0x0050                             /**< Determines scan window in units of 0.625 millisecond. */


static void on_ble_evt(ble_evt_t * p_ble_evt) {
switch (p_ble_evt->header.evt_id) {
  // ...
  case BLE_GAP_EVT_ADV_REPORT: {
    // Advertising data received
    const ble_gap_evt_adv_report_t *p_adv = &p_ble_evt->evt.gap_evt.params.adv_report;
    printf("RSSI: %d\n", p_adv->rssi);
    // also data, address, etc in p_adv
    break;
  }
}

ble_gap_scan_params_t     m_scan_param;
// non-selective scan
m_scan_param.active       = 0;            // Active scanning set.
m_scan_param.selective    = 0;            // Selective scanning not set.
m_scan_param.interval     = SCAN_INTERVAL;// Scan interval.
m_scan_param.window       = SCAN_WINDOW;  // Scan window.
m_scan_param.p_whitelist  = NULL;         // No whitelist provided.
m_scan_param.timeout      = 0x0000;       // No timeout.

err_code = sd_ble_gap_scan_start(&m_scan_param);

// and stop with
err_code = sd_ble_gap_scan_stop();

This seems to work, however the advertising window of 50ms / 100ms means that you do tend to miss things. Is it ok to put the window up to 100ms as well? It seems to work.

[Einar Thorsrud]

Thanks for posting your solution. That will be helpful for others with similar questions.