Banglejs2 becomes discoverable from time to time even when BLE is off

[espruino-discuss2]

Posted at 2023-07-24 by user156051

Hello,

I notice that even if I have turned off bluetooth BLE in the setting, sometimes, my computer can still discover the Banglejs2 by bluetooth. I can associate this with the "loading" message. When I open/exit an app and the "loading" message is shown, Banglejs2 becomes discoverable. I think it can be a privacy issue because the watch still broadcasts its presence while the bluetooth is supposed to be off. Is there a way to reliably turn off bluetooth ?

Steps to reproduce (you may need another device to scan for bluetooth devices):

1. Turn off BLE in the setting.
2. Exit from setting to the clockface.
3. Notice that Banglejs2 shows up on another device's bluetooth list.
4. Clear the bluetooth list by toggling bluetooth switch on another device.
5. Open an app (e.g. GPS Info)
6. Notice that "loading" message is shown and Banglejs2 shows up on another device's bluetooth list.
7. Clear the bluetooth list again.
8. Exit the app by holding the button for 2 seconds.
9. Notice the "loading" message and Banglejs2 is discoverable.
10. Open launcher by pressing button on clockface. No "loading" message is shown and Banglejs2 is not discoverable.
11. Back to the clockface by touching the "<-" icon on topleft of the screen. No "loading" message is shown and Banglejs2 is not discoverable.

[espruino-discuss2]

Posted at 2023-07-24 by Ivor

Someone correct me if I'm wrong... but I believe what's happening here is that during the bootloader the bluetooth hardware is initialised before espruino starts to run, the fact that your other device had stored the bluetooth mac address means that it detects, recognises and shows up the device during this process. Then once it boots the bluetooth is disabled.
This is how you can flash and update the device when it powers up/doesn't boot. I expect the bootloader code could be changed to not activate bluetooth at all, but would make it less user friendly if it needed to be bootable to be able to flash.
I guess/expect that code could be added to set a permanent flag that the bootloader could read during initialisation (although I've not looked at the bootloader code), but again that would open the possibility of ending up with a non-flashable device.

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Posted at 2023-07-24 by @gfwilliams

Do you have just the default apps on your Bangle, or do you have any other apps installed?

When the Bangle first boots, yes, it may show up on Bluetooth for a split second, however when swapping between apps with Loading... as you note, I'm pretty sure that the bluetooth advertising settings will be honoured.

What you may be seeing is a slight blip of advertising right after you initially exited the Settings app, while the 'Updating boot0' message was on the screen? But after that I'd hope it was ok.

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Posted at 2023-07-24 by user156051

Yes, I have other apps installed.

But I'm sure that it was Loading... on the screen when Bangle became discoverable. And I did some experiments to find that it won't advertise itself until I swap app (with Loading). However, the time window is usually short. If I try to connect to Bangle, the connection will fail and refreshing the bluetooth list will cause it to disappear. So my little theory is that, maybe bluetooth was turned on for a short time, before being turned off due to setting ?

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Posted at 2023-07-24 by @gfwilliams

Thanks - I just checked and even on a factory install I do see one advertising message pop up as you say.

It shouldn't be enough to connect to the Bangle with, but I'll look into it as it shouldn't happen - the boot code doesn't tell it to start advertising and just resetting the device shouldn't make it start to advertise.

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Posted at 2023-07-25 by user156051

Thank you so much for your prompt action!