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scanning and connection establishment parameters

Matej

Hi,

I have a question about scan window and interval [I'm using nrf51822aa with s130 2.0.1... I performing some tests and I find a use case: If I set both of them (scan interval and window) to 0x140 - 200ms then radio scans all the time, after that I stop the scanning and create connection...

Once I get event that connection is established (with connection interval 20ms) I would like to start scanning once again - with same scanning params (interval 200ms and window 200ms) - What is from my perspective not possible because scanning procedure could not use radio for 100% if connection is established... but softdevice allows me to use such params (I get NRF_SUCCESS) - even it's not possible to work with such params or am I wrong? Of course none of device is found - once I use a bit more reasonable params (interval 200ms, window 50ms) everything works just fine

Now I am wondering how is this solved/protected in softdevice that user can set such things for scanning or creating connection params?

I expose softdevice functions to end user via API with all supported params, but I see that user could also enter/trigger some strange behaviour... Should I limited user at entering params considering on number of established connections?

Thank you for info.

Best regards, Matej

  • 0 in reply to Petter Myhre

    I came up to such conclusion with reading doxygen comment sd_ble_gap_scan_start of function... where is written: "Not enough BLE role slots available. Stop one or more currently active roles (Central, Peripheral or Broadcaster) and try again"

    Considering priorities... then peripheral link should not starve, because of such scanning parameters. Peripheral link have the highest priority while observer/broadcaster is on the 3rd place.

    After all, I assume that in case if I already have established connection peripheral or central and then I call function to scan with 100% of time. I should get error NRF_ERROR_RESOURCES - considering to description.

    Or when it is possible to trigger that error?

    Thank you for additional info Petter.

    BR, Matej

  • 0 in reply to Petter Myhre

    I see. You can get the NRF_ERROR_RESOURCES if you for example have configured the SoftDevice to have 0 central links, and you try to scan.

  • 0 in reply to Petter Myhre

    Hm, ok... in that case is doxygen comment maybe a bit misleading.

    We have configured SoftDevice to support 1 peripheral link and 2 central links... We ( your SoftDevice ;) ) also support observing and broadcasting and we expose all of that to end customer. It's a bit hard to say how to limit user with those params; some of customers need just observer, other needs advertising + peripheral link and of course some of them need whole package (1+2, Observer or Broadcaster). Your SoftDevice is amazing and I somehow expected that you also have check for configuration which is actuall not possible from timeslot perspective.

    Probably you have some reason that this is done in that way and you not limiting end user... What about priorities, why peripheral link gets on hold and observer gets higher priority?

    Thank you

  • 0 in reply to Petter Myhre

    The peripheral link doesn't normally get on hold, but a scanner/observer can get higher priority.

    Normally both will be in Fourth priority - All BLE roles in states other than above run with this priority.

    A scanner can get Third priority - Advertiser/Broadcaster/Scanner which has been blocked consecutively for a few times.

    A peripheral link can First priority - Connection as a peripheral that is about to time-out

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