Accuracy of advertising duration and BLE_GAP_EVT_ADV_SET_TERMINATED

[Bruno Randolf]

Hello,

Using sd_ble_gap_adv_set_configure() with ble_gap_adv_params_t I observe that the actual time when the BLE_GAP_EVT_ADV_SET_TERMINATED event is raised is earlier to the duration that I specified in ble_gap_adv_params_t.

For example if i set duration to 2000ms (duration set to 200) and the interval to 500ms, the terminated event comes after around 1517ms... or if I use a duration of 2000ms and interval of 1000ms, the terminated event may come after 1007ms... if i use smaller values for interval, the timeout gets more accurate.

It seems the SoftDevice is stopping the advertising as soon as no next beacon fits into the duration time span... i just wanted to confirm this understanding with someone who has insight into the SoftDevice to make sure I don't have it wrong. Thanks.

[Vidar Berg]

Hello,

Yes, the advertising set will get terminated after the last advertising event has been processed by the stack. Also, the reason you got 3 and not 4 packets with the duration set to 2000 ms is that each adv. event are prefixed with a random 3-13 ms delay as required by the spec, so the actual interval ends up being between 503-513 ms (see  "Advertiser timing").

Best regards,

Vidar