S130 max concurrent central connections

[Cetin Mericli]

I am developing an application where a repeater unit connects to a number of other units, gets some info, aggregates it and broadcasts it as a peripheral unit (in a tree structure, the consolidated readings are propagated all the way up to a main receiver unit). Considering S130 as a combination of S110 and S120, I've always assumed that the max. number of concurrent connections are 8 (as it is in S120). However, when I try to connect more than 3 peripherals, I get NRF_ERROR_INTERNAL. I recently noticed that in the softdevice specification document for S130, it says max 3 central connections. I am using S130 v0.9 alpha, and nRF SDK 7.1.

So my question is two fold: i) is it true that S130 only supports up to 3 concurrent central connections? and ii) if so, what can I do to remedy that.

Many thanks in advance!

[Hung Bui]

@Cetin: i) Yes, it's true. S120 supports up to 8 central connections because it doesn't have peripheral role as with S130.

ii) Not much can be done to change that, at least for now. Future version of S130 may support more than 3 but that not what I can confirm. What you can do now if you want is to implement your own central role using timeslot API, but I don't think it's would be very straight forward and simple task.

[Hung Bui]

@Cetin:

I am not sure which could be easier, both approaches will have to deal with scheduling the manual connection event, 8 centrals links with 20ms interval will occupies the whole timeslot for radio. So the connection interval should be >20ms if you want to add a peripheral link in. Also, I don't think you would be able to support 6 packets per connection interval on the peripheral link.

There is no official information on the limiting factor on S130 that limit it to 3 central links. So I can't expose anything about that here.