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

[Petter Myhre]

Yes, the SoftDevice will accept such parameters even though it has a connection. It will schedule connection and scanning events. See this for more information about scheduling.

The SoftDevice does not protect against this, it expect the user to select paramters that make sense.

I absolutely think it makes sense to limit the parameters the user can enter.

[Matej]

Thank you for info Petter! So I also should take in account number of established connections and all of connection intervals - which also should use multiple to avoid some possible schedule collisions? In case that some of device would like to update/change connection interval – is it on my side that I check if this proposed connection interval is acceptable according to already connected devices and intervals that are already used?

Thank you.

BR, Matej

[Petter Myhre]

I guess you should, but it is up to you :) The central device dictates the connection interval, the peripheral can only request a connection parameter update, the central decides if it wants to accept or reject. See this MSC.

[Matej]

Hi, it's been a while since this topic... So I'm wondering if there are some news about that.

I have established peripheral link and after that user start scanning (sd_ble_gap_scan_start) with interval 200ms and also window 200ms. Of course such parameters are not possible, because part of timeslot is already used for peripheral connection – so scanning with such configuration is not possible.

Regarding to this chapter somehow I expect to get NRF_ERROR_RESOURCES error. But actually peripheral connection is terminated and scanning is started. What do you suggest? Except limiting user to enter such parameters.

Thank you for update ;)

BR, Matej

[Petter Myhre]

News about what? :)

It is possible to tell the SoftDevice to use those parameters, but it will of course not be able to scan 100% of the time and maintain a connection, the scanning and connection events will be scheduled according to the chapter you linked to. I don't see how you end up with expecting NRF_ERROR_RESOURCES by reading that chapter, could you explain a bit more?

The peripheral connection isn't necessarily terminated, but it depends a bit on the connection parameters. It can hit the supervision timeout and get linkloss. I don't have any other suggestions than limiting the user to enter such parameters.