How to enforce connecting to a specific master when bonded to many.

RE: How to enforce connecting to a specific master when bonded to many.

Petter Myhre — Mon, 30 Jan 2017 12:38:22 GMT

Correct. That is not possible with any of the SoftDevices for the nRF51, it is possible with the S132 4.0.0-2.alpha SoftDevice available for the nRF52832.

RE: How to enforce connecting to a specific master when bonded to many.

Francesco — Fri, 27 Jan 2017 10:37:29 GMT

Hey Petter. Sorry for missing that important detail. Your approach sounds very promising. I still wonder if we could build that fully automated. I.e. even disconnect the connected peripheral if another peripheral requests connection and is closer than the connected device at that time. That would require advertising and a connection being enabled a the same time. But that's not possible, right?

RE: How to enforce connecting to a specific master when bonded to many.

Petter Myhre — Thu, 26 Jan 2017 14:50:11 GMT

The new device cannot connect, it is not possible. A peripheral can only be connected to one central. So you always want to be connected to the closest central? You could have added that piece of information is the question ;)

An idea is to first do scannable non-connectable advertising, then you will get a BLE_GAP_EVT_SCAN_REQ_REPORT event every time a central scans your advertising packet. With it you will get the RSSI and the peer address. Then you switch to connectable advertising, with the peer address of the best RSSI in the whitelist.

After you have connected you can start doing scannable non-connectable advertising, and monitor continue the RSSI values to see if another central gets closer. If it does, disconnect from current connected central and do connectable advertising, with the peer address of the new central in the whitelist.

RE: How to enforce connecting to a specific master when bonded to many.

Francesco — Thu, 26 Jan 2017 12:33:27 GMT

I think I understood your approach, but I guess it only helps in a 2 centrals, one peripheral. You'd delete the currently connected device from the whitelist until the other device is connected. Then put the first device back to the whitelist. Right? With 3 centrals around, that doesn't solve the problem (completely).

RE: How to enforce connecting to a specific master when bonded to many.

Francesco — Thu, 26 Jan 2017 12:27:02 GMT

2 suggestions: 1) disconnect from all devices and hope the closest will take over the connection. That's very random I think. 2) Narrow down TX power on the peripheral for X seconds. But that may vary as well as we cannot influence the tx power of the centrals nearby. Both suggestions seem not very stable to me.

RE: How to enforce connecting to a specific master when bonded to many.

Francesco — Thu, 26 Jan 2017 12:27:00 GMT

So you mean a whitelist for active connections (i.e. who would see the peripheral when it advertises itself)?! Still in my scenario the peripheral would already be connected to a central device. Now another NEW central should get priority and the ability to steel the connection. I think a whitelist is not a solution here as we want to allow that new device to connect as well. Rather we need a solution to steel the connection from other connected centrals. The user which gets that priority is the one standing closest to the peripheral at that time. So we could identify that person via a hardware button he needs to press to take over the connection. Question though is what would be the appropriate technical solution.

RE: How to enforce connecting to a specific master when bonded to many.

Petter Myhre — Thu, 26 Jan 2017 10:13:49 GMT

Why is that an issue? Just remove them from the whitelist. You can keep the bond to the other centrals even though they are not in the whitelist.

RE: How to enforce connecting to a specific master when bonded to many.

Francesco — Wed, 25 Jan 2017 17:31:26 GMT

Thanks for the quick response. The issue with that approach is that all the other centrals are basically on the whitelist. In the scenario I mentioned originally we need to disconnect other connected centrals to enable a specific central to connect with the peripheral. Kind of a temporary kill-switch for the BT connection.

RE: How to enforce connecting to a specific master when bonded to many.

Petter Myhre — Wed, 25 Jan 2017 13:50:47 GMT

As a peripheral it can only be connected to one central at the time, if it is connected to a central it has to disconnect from that central before another central can connect.

If you only want a specific central to connect you should advertise with a whitelist and put the address of the specific central into the whitelist.