[Bug] cityhub goes into rapid constant blinking on button-press to power-off

[BertLindeman]

Describe the bug
What is the problem?
Button-press and keep to power-off sometimes ends with a rapid constant-blink situation.
Need to take out the battery to repair.

To reproduce
Steps to reproduce the behavior:

1. install CI-firmware ci-build-4515-v4.0.0b3-2-gf3f6ccbe on 2025-12-08 on a cityhub
2. Button press the cityhub to start
3. Button press and hold to power-off
4. When the hub starts blinking to indicate power-off, quickly release the button
5. If the hub keeps rapidly blinking, you need to remove the battery

Expected behavior
What did you expect to happen instead?
A simple power-off would be the expected action.

Screenshots
There is a saying that a picture is worth a 1000 words. Screenshots really help to identify and solve problems.

Extra info
Was trying to see if #2176 did re-occur.
Could not reproduce, so fine.
But out of ten power-off test the constant-blink situation occurred once.
Next tests took ~40 attempts.
This is very hard to reproduce, but seen twice in a few minutes.

[laurensvalk]

Was this without Pybricks Code or other Bluetooth devices connected?

Does this also occur on Technic Hub and City Hub?

[BertLindeman]

Was this without Pybricks Code or other Bluetooth devices connected?

Correct, just the cityhub without PC connection, no devices connected, no BT connection.

Does this also occur on Technic Hub and City Hub?

Will try the TechnicHub later today. Did you mean MoveHub?

[BertLindeman]

Just over a hundred attempts did not show this on a Technic Hub on the same CI-build firmware.

[laurensvalk]

Wow, thanks!

[BertLindeman]

Just to be sure all at github hash f3f6ccbe
retested Cityhub hit at ~ 50 attempts (was getting affraid it might be more than 100)

Tested the rest with just over 100 attempts
Movehub - no problem found
Technichub - no problem found
Primehub - no problem found

Not tested the EV3 and NXT

Only slightly related
Did not know that there is a difference between the primehub and the City-, Move-, Technichub in the power-off.
All start OFF, no devices:

1. Primehub: press and hold the center button: Hub goes on (keep pressing) - hub goes off
2. The other hubs: press and hold the center button: Hub goes on (need to release the button); press and hold the center button: Hub goes off

[laurensvalk]

I think I might have found a potential cause for this while cleaning up some Bluetooth code.

peripheral_singleton.con_handle is not initialized at NO_CONNECTION, so this will return true even if there is no peripheral. Attempting to disconnect anyway then causes a null dereference which may cause the crash.

    if (connection == PBDRV_BLUETOOTH_CONNECTION_PERIPHERAL && peripheral_singleton.con_handle != NO_CONNECTION) {
        return true;
    }

Actually, that is not true.