Why, sometimes, do I need to restart the iOS Bluetooth (using the system button) to make my central manager able to connect successfully?

Question

I'm developing an application on iOS and OS X Yosemite which is using CoreBluetooth on iOS and IOBluetooth on Mac. The iOS app plays the "central" role while the Mac app is playing the "peripheral" role.

Basically, the iOS app (the central) starts a scan to find peripherals and when it finds a Mac advertising peripherals data, the central connects to it and can discover its services and characteristics.

My problem is that sometimes, I don't know why, the iOS app starts a scan to find a Mac advertising and when it finds it (this step work all the time), it tries to connect to it but never succeed.

To make it able to connect successfully to the peripheral again, I need to turn off and then turn on the Bluetooth from the iOS button.

Another strange thing is : imagine the central is in the same situation (trying to connect with no success). On OS X if I click on the Network icon (with the Wifi symbol) in the system status bar, then it will display the list of all available Wifi networks, and when it adds to the list my iPhone as a "Personal hotspot", at this time the central (which is on the iPhone) manages to connect to the peripheral (the Mac).

With this problem, the app usage is a lot compromised because randomly the iPhone will not be able to connect to the Mac.

I spent a lot of days on the internet (Google, Stackoverflow, ...) to find similar cases. I read a lot of articles and tried a lot of things like stopping the scan and starting it again if the connection didn't succeed after 10 seconds for example.

Don't hesitate to tell me if my question is not clear. I will update it if needed.

Thanks a lot in advance for your help. I really need to find a way to fix this.

Answer 1

I don't have an answer (and not enough rep to comment) but I have been experiencing a very similar problem for months now. My iOS app which is playing the central role sometimes fails to discover services on the peripheral (linux) which can only be fixed by power cycling the bluetooth radio on my iOS device via settings/bluetooth. After bouncing the bluetooth radio, peripheral discovery appears to works perfectly.

I've found two reproducible cases: (1) If on my peripheral I completely swap out the service being advertised (i.e. change the service UUID and all characteristics) then the iOS peripheral will detect the peripheral with this new service during the scan, but service discovery fails. I find that peripheral:didDiscoverServices gets invoked, but the list of services is empty for this peripheral. (2) If on my peripheral, I modify the list of characteristics in any way (add a new one, remove one) the iOS app does not notice this change at all. During characteristics discovery, the same list of characteristics (prior to modification) is presented. Again, power-cycling the bluetooth radio on the iOS device appears to be the only thing that fixes this.

It appears as though iOS is caching BTLE peripheral services and characteristics upon discovering a new peripheral and the only way to flush this cache is to power cycle the bluetooth radio.