[Bug] Peripheral connection issues

[laurensvalk]

Describe the bug
There are a few distinct issues that need fixing:

• When Bluetooth causes a soft shutdown, the shutdown animation blink is not visible, making it look like a hard crash.
• When initialization fails for any reason, you get RuntimeError: Can use only one Remote if you try a second time
• Connecting to the Xbox Controller waits indefinitely if the controller is not in pairing mode. It should give up and raise an error (like it used to in V3.6.1)
• Error propagation from the Bluetooth task handling loop is not done correctly, so we don't see all errors.
• Update scanning to match new peripheral objects

[laurensvalk]

When initialization fails for any reason, you get RuntimeError: Can use only one Remote if you try a second time

Maybe this is the universe calling to finally properly support more than one peripheral. 🤔

[laurensvalk]

When initialization fails for any reason, you get RuntimeError: Can use only one Remote if you try a second time

This is happening due to the finalizer. It goes something like this:

1. Remote allocates an object and data buffers
2. You disconnect and create a new remote, creating new data buffers.
3. Only now the first object is garbage collected, which on close unsets the buffers to avoid use after free.

Only now the new Remote does not have any data buffers, so it connects but won't process new notifications. So, this program only reads buttons the first time:

from pybricks.pupdevices import Remote
from pybricks.tools import StopWatch, wait

for i in range(3):

    r = Remote()

    watch = StopWatch()

    last = set()

    while watch.time() < 5000:
        pressed = r.buttons.pressed()
        if pressed == last:
            continue

        last = pressed
        print(pressed)

    r.disconnect()

    wait(1000)

[laurensvalk]

When initialization fails for any reason, you get RuntimeError: Can use only one Remote if you try a second time

Maybe this is the universe calling to finally properly support more than one peripheral. 🤔

So let's start by allowing just one, but make some preparations in this direction to fix the issue at hand. For example, we'll introduce:

pbio_error_t pbdrv_bluetooth_peripheral_get_available(pbdrv_bluetooth_peripheral_t **periperal)

So we can properly assert that it is not connected or not currently busy connecting.

The peripheral notification callbacks will be passed a reference to the peripheral (this is the new part).

/**
 * Callback that is called when peripheral sends a notification.
 *
 * @param [in]  periperal   The peripheral that sent the notification.
 * @param [in]  data        The data that was received.
 * @param [in]  size        The size of @p data in bytes.
 */
typedef void (*pbdrv_bluetooth_peripheral_notification_handler_t)(pbdrv_bluetooth_peripheral_t *periperal, const uint8_t *data, uint32_t size);

[laurensvalk]

All resolved, or should be! Happy to get some @BertLindeman testing! 😄

[laurensvalk]

This needs some further work.

[BertLindeman]

Not sure if this is the correct place to report, but commits here might have to do with power-on / power-off.

Test: install on CityHub:
Pybricks MicroPython ci-build-4577-v4.0.0b3-66-gfcfdf4e0 on 2026-01-02; Powered Up City Hub with STM32F030RC

Connect the hub via BT to pc beta.pybricks.com
Did not run a program.
Long press hub button to power-off.
Release the button at the moment the led starts to blink.
Do not re-connect to the pc and repeat:
long press to power-off. Release the button at the moment the led starts to blink.
Did it ~30 times

1. Once into fast blinking, so I needed to pull the battery
2. Two times after power off the hub restarted.
3. The hub did not restart if I keep the button pressed for ~ half a second after power-off

Test TechnicHub
This program (xbox_technichub_issue_2521.py):

from pybricks import version
from pybricks.hubs import ThisHub
from pybricks.iodevices import XboxController
from pybricks.tools import wait
from pybricks.parameters import Color

hub =ThisHub()
waittime = 1  # was 10
print(f"Waiting {waittime} seconds")
hub.light.on(Color.ORANGE)
wait(waittime * 1000)
print(f"Waited {waittime} seconds now try to connect")
ctrl = None
while not ctrl:
    wait(5)  # to show the previous print
    hub.light.on(Color.BLUE)    
    wait(5)  # to show the previous print
    hub.light.on(Color.RED)
    ctrl = XboxController(stay_connected=True)

hub.light.on(Color.GREEN)
print("connected")
wait(5000)

Obvious that the hub led goes red and stays red until connected.

Set the xbox controller to "pairing" (before this it was paired to another hub)

Run the program connected to beta.python.com
Windows message: xbox controller wants to connect - Press dismiss

While connected to PC, the attempts to connect (in pairing mode) do not succeed.
Did not see a steady led on the controller.

Uncouple from PC.
Press hub button to restart (controller is still in pairing mode)
Hub goes via RED to GREEN and controller led goes steady.
Not sure in which phase the connection did pair.

It does not matter if I run the program before or after the controller is switched on (no more in pairing mode)

hard to recreate:
One time the hub light was RED (waiting to be connected)
a long press of the hub button made the hub go into rapid flash that needed the battery removal.
Was NOT able to recreate this.
And not sure if the hub was really connected to the PC. But I do think so.

[BertLindeman]

Ran this slightly adapted program (print after disconnect, so I know) on the cityhub.
Firmware Pybricks MicroPython ci-build-4577-v4.0.0b3-66-gfcfdf4e0 on 2026-01-02; Powered Up City Hub with STM32F030RC

from pybricks.pupdevices import Remote
from pybricks.tools import StopWatch, wait

for i in range(3):

    r = Remote()

    watch = StopWatch()

    last = set()

    while watch.time() < 5000:
        pressed = r.buttons.pressed()
        if pressed == last:
            continue

        last = pressed
        print(f"{r.name():<30} {pressed}")

    r.disconnect()
    print("disconnected")
    wait(3000)   # was 1000 but maybe wait until this remote is no longer trying to connect?

print("end of program")

After some rounds in the same program (connected to the PC too, so I could see the prints)
connecting to left remote and right remote, it went well,
until I saw no more prints and the city hub as stil slowly fade-in - fade-out, so running.
But I could not access the log window to CTRL-C and see where the program was running.
So long-press the hub button. Results in rapid flashing the hub. Battery pull was needed.

This was well recreatable, each time, even once before the remote got connected.

The same result with Pybricks MicroPython ci-build-4577-v4.0.0b3-66-gfcfdf4e0 on 2026-01-02; LEGO Technic Hub with STM32L431RC

Maybe this is caused by two remotes advertising (if that is what they do) at the same time?

This did not occur on the RobotInventor on the same firmware Pybricks MicroPython ci-build-4577-v4.0.0b3-66-gfcfdf4e0 on 2026-01-02; SPIKE Prime Hub with STM32F413VG

Although I saw once two blue leds at the same time on the two remotes.
But They went out quickly and the program ended normally.

No excuse for mistakes, but I still have a hazy head due to tired and still the flu.