uart_service example connects and disconnects

[nastiliano]

Hello everybody.

I'm trying to implement a bidirectional comunication between my PC (Python - Bleak) and a ESP32 (Micropython - bluetooth uart), because I'm able to comunicate these with GATT characteristics but is too slow just for send 1kB.

With bleak example (https://github.com/hbldh/bleak/blob/develop/examples/uart_service.py) and micropython example (https://github.com/micropython/micropython/blob/master/examples/bluetooth/ble_uart_peripheral.py) I can connect the devices but immediately the connection disconnects.

In ESP32 device I can see the IRQ getting the connection and immediately a disconnection IRQ occurs.

Could you help me please??

Thank you very much.

[dlech]

Logging Bluetooth packets as described in the troubleshooting page of the Bleak docs is the best way to solve problems like this.

[dlech]

Did you have to enter a pin code when pairing? If yes, then pair() isn't going to help.

Or sometime connects and gets just 1 string from ESP32 and disconnects

If you can do the Wireshark logs again while reproducing this problem, we could try to see what is happening there. It could be the same problem or a different problem.

[nastiliano]

Hello,

Now the error is different.

In terminal appears:

    Device was disconnected, goodbye.
    Exception in callback Future.set_result()
    handle: <Handle Future.set_result()>
    Traceback (most recent call last):
      File "C:\Users\...\AppData\Local\Programs\Python\Python313\Lib\asyncio\events.py", line 89, in _run
        self._context.run(self._callback, *self._args)
        ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    asyncio.exceptions.InvalidStateError: invalid state

And the Wireshark file is:
BLE.zip

I tried with 2 micropython codes:

• The Low level BLE UART example
• An aioble exaple from a Github user
  The result is the same.

Thank you very much

[dlech]

The InvalidStateError comes from asyncio and means there is probably a bug in the Python code somewhere. However, the stack trace doesn't give enough information to see where the bug is actually coming from, probably due to the winrt package being a binary extension. The exception is probably due to a Future from a winrt async mentod being canceled because of the disconnect and then the Windows API callback trying to set a result on a canceled Future. But fixing this bug won't fix your problem.

The disconnect happens immediately after reviving an "Encryption Change" event. This event says that the connection timed out. So Windows is just reacting to this and disconnecting the device since encryption couldn't be established. So likely the problem is with the peripheral firmware.

You could also try removing the device using the Windows Bluetooth settings and try again. Don't use the Windows Bluetooth settings to scan/connect/pair the device after removing it, just use Bleak.

[nastiliano]

Finally!!!

I removed the Windows 11 pairing and it works perfect.

Thank you very much!

PD: Now my objective is sending JSON serialized data up to 16kB. I've seen that I can send large string and my ESP32 code (buffer) slices the data but my question would be. What would be the best method to send/receive JSON serialized data using the max buffer size or withous slicing? Or I don't know... What would be your tip?

[nastiliano]

Hello, I'm going to answer me in order to help everyone with the same problem:

For send long data serialized in JSON just modify the Bleak example like:

        def sliced(data: bytes, n: int) -> Iterator[bytes]:
            """ Slices *data* into chunks of size *n*. The last slice may be smaller than *n* """
            return takewhile(len , (data[i : i + n] for i in count(0, n)))            
         
        for s in sliced(json.dumps(data).encode() , rx_char.max_write_without_response_size):
            await client.write_gatt_char(rx_char , s , response = False)
        
        await client.write_gatt_char(rx_char ,  b"\r\n" , response = False)

Thank you very much. Best regards