Keeping track of BLE connection state: connected or not, advertising or not, etc

[mrono]

Hello.

First some background:

I have an application running on nRF52840. Development began with the nRF52832 using nRF SDK 13 or 14. Then migrated to 15.2, 15.3, and finally to 17.0.2. The application is a BLE peripheral. The basic bluetooth connection code was written following the examples of those SDKs plus a Nordic tutorial on adding a custom BLE service. The code related to making and maintaining a BLE connection has been fairly stable for a long time. But recently I had a need to add a simple new feature, and that got me looking at the code more closely again. And to compare it to the examples of the current SDK 17.0.2.

My question really is what is the current best practice for keeping track of the state of the BLE connection? Ie, Are we currently connected? Are we currently advertising? Bonded or not? Etc.

My code is based on the examples of earlier SDKs, so I'm keeping track of state in the application code. For instance the connection state is held in a variable called m_conn_handle, and updated whenever the application code receives events from the BLE libraries. This is similar as in many of the examples. I was aware that the Connection State module existed, but had not looked at it closely before. It looks like I could simply use the ble_conn_state_peripheral_conn_count() -function to tell if I'm currently connected or not. But even the newer examples aren't using this.

Likewise for the advertising module. I'm keeping the state (currently advertising or not) in application code, updating the variable based on events. My recent changes revealed that I wasn't reacting to all possible events, and the application level state variable wasn't always in sync with the advertising module. I'm not sure how I could ask the current advertising state from the advertising module, but surely the module must know it. If I could let the module keep the state and just ask for it when needed, I could eliminate the source of the error I just encountered.

A third example is the whitelist. I was keeping (a copy of) that too in application code. I believe that in some earlier SDK it was necessary. Also you got duplicates on the list if you allowed repairing. It looks like this might no longer be necessary.

So what is the current best practice? Could I let the BLE libraries handle all state management? I'm mainly concerned that the application level state variables might not stay accurate if I fail to catch all events.

[Simonr]

Hi

I would suggest checking out how this is handled in our most recent multi-link example, as that is the method by choice our SDK team uses to keep track of connection states. Please check out the BLE Link Context Manager and Connection State libraries as well.

Best regards,

Simon

[mrono]

Thank you. I hadn't realized I should take a look at the multi-link example. It looks like the connection state module is the right one for my simple one connection at a time -scenario. The multi link example shows nicely how to use it. This library could be used in some of the simpler examples as well so it would not go unnoticed.

The link context manager seems to be for keeping some additional data related to separate connections. It is not entirely clear to me when I'd want to use it though. The infocenter page lists examples, even the NUS service, but I'm still not sure I get the point of it. Would I use this if I wanted my service to serve different data depending on who the client is?

That leaves only the advertising module, which was the source of my original issue. I need to keep track of the advertising state, ie are we currently advertising, and if so are we using the whitelist or not. I can look at the whitelist state from:

m_advertising.adv_modes_config.ble_adv_whitelist_enabled

For the general "Are we advertising" -question I tried this:

if(m_advertising.adv_mode_current == BLE_ADV_MODE_IDLE)

But the adv_mode_current doesn't always show the current state. And according to this it should not be used the way I'm trying to use it. I have now gone back to keeping track of the advertising state by updating a variable every time I receive an advertising event.

So the one open question I still have is: Can I somehow ask the advertising module if we are currently advertising?