Scanning at low priority / pre-emptive scan?

RE: Scanning at low priority / pre-emptive scan?

TylerD — Mon, 21 Sep 2020 11:59:36 GMT

Ok thank you very much, this is clear now.

RE: Scanning at low priority / pre-emptive scan?

Kenneth — Mon, 21 Sep 2020 11:52:14 GMT

There is no logic in the softdevice that reduce the size of the scan window or interval due to connection events. The scan event will once scheduled allocate the entire scan window. The next scan window is calculated after the previous scan window is finished, if the next calculated scan window is already taken by a connection event, then the scan window is skipped by one scan interval period (or several periods if there are multiple connections that may be active).

By having shorter scan window and intervals than connection intervals, the connection intervals will always be able to schedule the next connection event before it can be used by the scan event.

RE: Scanning at low priority / pre-emptive scan?

TylerD — Mon, 21 Sep 2020 11:41:10 GMT

Ok, thanks for the fast answer. Just to verify: the 10ms/10ms scan timing means that the scan window will start at most every 10 ms?

If I understood right, the connection events will take higher priority and the scan is executed after connection events are handled. That would mean the actual scan interval will be much smaller than 10ms, depending on how many active connections there are. ?

RE: Scanning at low priority / pre-emptive scan?

Kenneth — Mon, 21 Sep 2020 11:08:46 GMT

Hi,

For the scanning to have minimum impact on the current connections, I recommend to set scan window and interval to small values, e.g. 10ms / 10ms. The scanning will then be interleaved between active connections. This is because typically connections will have longer interval, and thereby will be able to schedule the next "slot" well ahead of when scanning will try to request the same "slot".

Best regards,
Kenneth