Advertising/Scanning Problems

[Yaroslav]

Issue is similar to devzone.nordicsemi.com/.../

I'm developing an application based on latest SoftDevice 130_1.0.0 and using two or more DevKits. My application starts advertising and scanning simultaneously with parameters:

	adv_params.type        = BLE_GAP_ADV_TYPE_ADV_IND;
	adv_params.p_peer_addr = NULL;                           			
	adv_params.fp          = BLE_GAP_ADV_FP_ANY;
	adv_params.interval    = BLE_GAP_ADV_INTERVAL_MIN;
	adv_params.timeout     = BLE_GAP_ADV_TIMEOUT_GENERAL_UNLIMITED;

	if(adv_mode == LIGO_ADVERT_MODE_CONNECTED)
	{		
		adv_params.type		= BLE_GAP_ADV_TYPE_ADV_NONCONN_IND;
		adv_params.interval	= BLE_GAP_ADV_NONCON_INTERVAL_MIN;
	}

	scan_param.active = 0;
    scan_param.selective = 0;
    scan_param.p_whitelist = NULL;
    scan_param.timeout = 0;
    scan_param.interval = 0x03C0;		// 600 ms
    scan_param.window = 0x0140;		// 200 ms

Each board using LED indicates receiving advertise reports.

So, I've noticed next:

1. When I reset(or power on) two board at the same time - both boards don't indicate anything, it means there are no incoming advertising packets. Seems, nRF during scan doesn't advertise.

2. When I reset(or power on) two board at different time - they both work fine but after some time (adout 15-30 min) I see that advertising's appear much rarely up to total stopping receiving adv packets for few minutes and then I see advertise packets again.

3. When I set next scan interval = window, like:

   scan_param.interval = 0x03C0; // 600 ms scan_param.window = 0x03C0; // 600 ms I don't see any advertising using nRF MasterControlPanel for PC and/or for smartphone. Also both boards don't indicate anything.

4. When I start a app_timer() in advertising report handler I notice that scanning activity becomes worst - I can see indications very rare.

So, could you explain this behavior?

[Petter Myhre]

2. Edit 17.06.2015, my previous clarification of the behavior was incorrect. Sorry. Please see below.

Could you clarify behavior at the next timings: - adv interval: 100mS - scan window: 200mS - scan interval: 600mS

Let assume that scan starts first, then: 0-200ms scanning

~200 adv

~300 adv

~400 adv

~500 adv

~600 adv

800-100 scanning

and so on...

So, is in correct?

advertising interval = advInt = 100ms random delay = ranDel = 0-10ms

You start with a scan of 200ms, after the scan window ends the scanner will try to schedule a timeslot for the next scan window, 400ms later.

The ~0ms advertising event is blocked, since a scan is ongoing. The advertiser will try to schedule a timeslot one advInt+ranDel later. It will be blocked again, then the advertiser will try to schedule a timeslot advInt+ranDel later, and it will succeed. When the advertising event ends the advertiser will try to schedule a timeslot for the next advertising event, advInt+ranDel after the start of the previous one. It will succeed. And so on.

There is a scan window scheduled to start at 600ms. So when the advertiser tries to schedule a timeslot inside it, it will be blocked. The advertiser will try to schedule a timeslot one advInt+ranDel later. If it is blocked it will try to schedule a timeslot one advInt+ranDel later. And so on.

3. I have just tried an advertising interval of 20 ms, scan window=scan interval=100ms, and scan before advertise with both s130_nrf51_1.0.0-3.alpha_softdevice.hex and s130_nrf51_1.0.0_softdevice.hex. They are both advertising and their behavior seem identical in the sniffer log.

[Milan]

Hi petter,

what will happen if scan interval = 3.125ms scan window = 2.5ms advt interval = 20ms

I am trying to understand it more deeply. Your help will be appreciated.