stop/startAdvertising do not work well for advertising interval to be shorten

Mbed OS
,
1

I’m testing with ARMmbed/mbed-os-example/BLE_Advertising/source/main.cpp.
Working with Mbed Studio, mbed os 6 and nRF52840 DK.

When the advertising interval is changed to 100ms and _event_queue.call_every() is set to 100ms, it works well. Using the nRF Sniffer, most of advertising interval are seemd nearly 100ms, like this figure.

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Attempting the advertising interval to be shorter than GAP_ADV_PARAMS_INTERVAL_MIN_NONCON (100ms), I modified _event_queue.call_every() handler.

        _event_queue.call_every(
            25ms,
            [this]() {
                update_battery_level();
                _ble.gap().stopAdvertising(ble::LEGACY_ADVERTISING_HANDLE);
                _ble.gap().startAdvertising(ble::LEGACY_ADVERTISING_HANDLE);
            }
        );

I was assuming before achieving an advertising interval 100ms, the advertising is stopped and a new advertising start at 25ms. But stopAdvertisng() adn startAdvertising() do not work effectively. The nRF Sniffer shows many of advertising interval are still about 100ms.

fifure_2
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Any misunderstanding or mistake are there?
What should I do any more modification?

2

I’m assuming you mean this source code: https://github.com/ARMmbed/mbed-os-example-ble/blob/master/BLE_Advertising/source/main.cpp

Within this example, the advertising interval is defined here:

ble::AdvertisingParameters adv_parameters(
            /* you cannot connect to this device, you can only read its advertising data,
             * scannable means that the device has extra advertising data that the peer can receive if it
             * "scans" it which means it is using active scanning (it sends a scan request) */
            ble::advertising_type_t::SCANNABLE_UNDIRECTED,
            ble::adv_interval_t(ble::millisecond_t(1000))
        );

So if you want to change this to 100ms, or less change here ble::adv_interval_t(ble::millisecond_t(100))

I’m not sure stopping and starting advertising is required here. Usually you start advertising and leave it started as the battery level is updated within this function: _adv_data_builder.setServiceData(GattService::UUID_BATTERY_SERVICE, {&_battery_level, 1});

3

Thanks, Gerriko

Yes, I 've changed the advertising interval:

ble::adv_interval_t(ble::millisecond_t(100))

I understand that the minimum interval for Non-connectable property limited by GAP_ADV_PARAMS_INTERVAL_MIN_NONCON (100ms). I need to set a interval shorter than 100ms, so i’m trying to use stopping and starting.

Is there another idea?

4

No that’s a default parameter, should you not specify an advertising interval.
https://os.mbed.com/docs/mbed-os/v6.15/feature-i2c-doxy/class_gap_advertising_params.html#a1c0f0bc52e6a87281be7d16733a6c393

You can specify a much lower value. It was only the other day I used a 20ms interval and it worked fine.

5

Does not this code work?

(GapAdvertisingParams.h)

  140         } else if (_advType == ADV_NON_CONNECTABLE_UNDIRECTED) {
  141             /* Min interval is slightly larger than in other modes. */
  142             if (_interval < GAP_ADV_PARAMS_INTERVAL_MIN_NONCON) {
  143                 _interval = GAP_ADV_PARAMS_INTERVAL_MIN_NONCON;
  144             }
  145             if (_interval > GAP_ADV_PARAMS_INTERVAL_MAX) {
  146                 _interval = GAP_ADV_PARAMS_INTERVAL_MAX;
  147             }
  148         } else {

Cause of this, the interval cannot be shorten.

6

Ah, maybe this is where the confusion lies… and I wasn’t paying attention. Where did you find GapAdvertisingParams.h? If I search online it directs me to ARMmbed/ble which is out of date. All BLE libraries are already included within the mbedOS/connectivity folder (v6.15)

I also had sent the wrong link. The function to use is AdvertisingParameters

and not GapAdvertisingParams

7

Thanks, Gerriko

I comfirmed AdvertisingParameters.h. There is similar normalize functionality.

  600         if (_advType == advertising_type_t::NON_CONNECTABLE_UNDIRECTED) {
  601             _minInterval = adv_interval_t(std::max(_minInterval.value(), GAP_ADV_PARAMS_INTERVAL_MIN_NONCON));
  602             _maxInterval = adv_interval_t(std::max(_maxInterval.value(), GAP_ADV_PARAMS_INTERVAL_MIN_NONCON));
  603         }
8

Yes, that appears to be the case with NON_CONNECTABLE_UNDIRECTED. I’ve never investigated why that option differs from say SCANNABLE_UNDIRECTED, which I tend to use.

Got me puzzled…

EDIT.
So I had to find out… and came across this useful diagram online.

image
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source: https://www.researchgate.net/figure/Non-connectable-and-scannable-undirected-advertisement-detection-procedure_fig1_323898620

9

From additional my investigation, I’ve made a new thread;
When the timing for advertising to be active - Mbed OS - Arm Mbed OS support forum

Thanks.

10

I also had sent the wrong link.

11

I’m not sure stopping and starting advertising is required here. . .