point to multipoint with UART (multilink on the S120)

[snowball]

I'm interested in using BT LE to collect data from a number of serial based devices -- a point-to-multipoint configuration. I'm familiar with the UART examples and have seen the multilink example.

The "devices" would be connected to a BT "remote" via the UART (+ level shifter etc), any serial traffic needs to be sent over the BT LE link to a single master BT device connected to a PC which can read the data (probably via the UART again).

However, I'm not 100% sure of the model, maybe it's just the terminology. In the multipoint example, there is a central (Softdevice 120) and peripheral (Softdevice 110). The central connects to the peripheral(s) to collect data, which is the opposite to how I need it to work (or is this just convention and can either end initiate the xfer?).

Finally, what are the limitations, I think the multipoint allows up to 8 simultaneous connections, can I have more "parked" connections? i.e. how many device+BTLE "remotes" combinations can I associate with a single BT LE master? (even if only 8 can communicate concurrently).

Thanks!

[snowball]

In the SDK, I found a set of multilink app examples in Board/nrf6310/s120/experimental for both central and peripheral. It looks like this is exactly what I need, except that I need to (as Ole suggests):

1. Configure the peripherals to only advertise when they have data to send (or to change the advertisement payload to indicate how much data is available)
2. disconnect each peripheral after they are done with the data transfer

Presumably, if I want to "ping" a peripheral outside of when the peripheral has data to send, I can simply make a direct connection to it? Or does the peripheral have to always be advertising ...

[Ole Morten]

Considering that the minimum advertising interval is 20 ms, and a complete advertising event over 3 channels take in the order of 2 ms on-air you may get collisions if all 20 advertise at the same time. However, the advertising intervals are adjusted randomly to avoid consistent collisions, so I would not expect any serious trouble even if there are some collisions.

Also, if you're concerned about it, you can just increase the advertising interval to make this less likely, and based on your description it also sounds like all devices will not necessarily be advertising at the same time.